Indium Corporation Blogs

上周在圣地亚哥(San Diego), 业界一年一度的盛会APEX落下了帷幕。Indium公司一如既往地参加和支持APEX，并在会上发表4篇技术文章。

在展会上，我们介绍的重点仍然是Indium8.9系列的焊接产品。这些产品分有卤素和无卤素的(halogen contained or halogen free)，每种产品都有自己突出的特点，但是整个系列的产品都是针对免洗无铅(no-clean Pb-free)而设计的，可以与fine powder 兼容，能够很好的帮助客户解决枕头效应(head-in-pillow), graping 等问题。

Indium发表的技术文章可以在我们公司的网站上免费下载：http://www.indium.com/technical-documents/whitepaper/

• QFN Voding Control Via Solder Mask Patterning on Thermal Pad
• Material and Process optimization for HIP Defect Elimination
• Voiding Mechanism and Control in Mixed Solder Alloy System
• The Effects of Human-Induced Contamination on PCB Assembly Electrical Reliability

我很高兴能参加这次盛会，并见到了许多新老客户。期待明年4月份Las Vegas 的APEX.

Cheers!

PS: 隆重祝贺Indium公司的好朋友和我的好友，Intel公司的Raiyo Aspandiar 荣获Distinguished Committee Service Award (from IPC at IPC APEX EXPO in February in recognition of Raiyo’s outstanding contributions to the development of IPC-7095C, Design and Assembly Process Implementation for BGAs.) 实至名归！！…… 有的书把Steve Jobs 05年Stanford 演讲的名言”Stay hungry, stay foolish” 翻译成 “求知如渴，虚怀若谷”。 我觉得这是绝妙的翻译，也是Raiyo 的真实写照！！ 恭喜你Raiyo!!

Pic: Indium Corp

Folks,

I was at APEX 2013 San Diego this past week.  San Diego is a great venue for the show, but I always forget how cold it can be (55-65°F) this time of year.  The folks at iConnect 007 interviewed me at the show; the topic was lead-free reliability and has cost for consumer electronics been demonstrated.  You can see the interview here.

These are topics I think about often, so let’s discuss them a bit. First, let’s consider reliability.  RoHS was enacted on 01 July 2006, more than 6 ½ years ago.  Each year more than $1 trillion-worth of electronics are made, therefore, in this period of time, something over $3 trillion worth of consumer electronics have been manufactured.  There have been no “the sky is falling”-type of reliability issues in this time.  How can I say this?  Well, my office at the Thayer School of Engineering at Dartmouth is across the hall from the IT (information Technology) Dept.  They purchase all of the millions of dollars worth of PCs, printers, displays etc. that Thayer uses.  Several years ago (say early 2011) I stopped by when most of the department was in and cheerfully asked if the reliability of the equipment they purchase has gone down since lead-free assembly was enacted.  They asked me in unison, “What’s lead-free assembly.”  After I explained what lead-free assembly was, they confirmed that they have noticed no changes in reliability.  Since RoHS, my family has purchase about 100+ electronic devices, a few have had reliability problems, about as many as in the past.  Most were attributed to hard drive fails.  Of the scores of friends and colleagues I have, no one has ever commented that they have noticed an increase in electronics fails. So, my conclusion is that consumer product reliability is not "practically" worse if my family and  these many  other folks haven’t noticed it.

I have made an informal study of reliability data of lead-free vis-a-vis tin-lead solders published in papers.  A statement from Rockwell Collin’s JCAA/JGF-PP No Lead solder Project: -55C-125C Thermal Cycle Testing Final Report  sums up my overview conclusion nicely: “Test vehicles assembled with lead-free materials (notably tin-silver-copper) exhibited lower reliability under some test conditions.”  Nay sayers might be quick to suggest that this statement  says that lead-free is no good.  However, the statement could be reworded to say: “In considerably more than half of the test conditions, test vehicles assembled with lead-free materials had higher reliability." Counting the comparisons in the Rockwell Collins paper shows lead-free better in 51 cases, tin-lead better in 31 cases, and one draw.  However, it is disturbing that a small percentage of lead-free assembled test vehicles had much much worse reliability than tin-lead test vehicles.  This later information makes me believe that lead-free is not yet ready for mission-critical, high-reliability, long-life products.  These small numbers of much poorer reliability assemblies must be understood and corrected before lead-free is ready for mission-critical prime time.  The much shorter life cycle of today’s consumer electronics may also mask this concern.

What about cost?  I don’t at all want to minimize the expense that many went through to go lead-free and RoHS compliant.  In about 2007, one of our colleagues estimated that it cost the electronics industry $20 billion to become RoHS compliant.  I think this number is low, but, from a consumer’s perspective, there has been no cost hardship.  The price of a PC continued to go down during and after RoHS implementation, as shown in the figure below.  While performing my non-scientific survey of co-workers, family, and friends on reliability, I also asked about cost.  All agreed, electronics are cheaper than ever.

Challenges still exist, even in consumer electronics with the Head-in-Pillow, Graping, non wet opens, and other defects.  However, we can all purchase lead-free, RoHS compliant products at a reasonable cost and reliability.

Cheers,

Dr. Ron

The source for the image is :http://thomaslah.wordpress.com/2010/02/03/apple-and-intel-defying-gravity/

The 2013 IPC APEX Expo , the premiere electronics assembly event, is right around the corner - and our technology experts are ready to share their experience and knowledge on a variety of topics.

Ning-Cheng Lee, PhD, VP of Technology will present a paper on voiding control in mixed solder alloy systems. He will also present on the hot topic of QFN voiding.     Dr. Lee is a world-renown soldering expert (EVERYBODY knows Dr. Lee!).  In addition to his work at Indium with solders (for 27 years), he is also an expert on polymers, underfills, and adhesives.

Ronald Lasky, PhD, PE, Senior Technologist will be presenting a paper on Material and Process Optimization for Head-In-Pillow Minimization.  Dr. Lasky is one of our most popular bloggers, check out his blog!  He approaches the world of electronics assembly from some interesting directions, including the exploits of Patty and the Professor.  Dr. Lasky will also talk about Applications of Solder Preforms to Improve Reliability, and A Focus on Productivity: Several Case Studies.  He has also found some time to teach two professional development courses: An Introduction of DOE, SPC and Weibull Analysis; and Manufacturing for High Yields in Assembly. Another busy man!

Senior Technical Support Engineer, Eric Bastow will be presenting on The Effects of Human Induced Contamination on PCB Assembly Electrical Reliability.  Eric has looked at the impact of oil, grease, and hand creams and how they can create reliability issues in small components.  Eric provides technical support to our customers by phone and in person. 

The APEX Expo will feature over 400 exhibitors and lots of technical sessions. It provides you the opportunity to have face-to-face discussions with many of our materials experts, so bring your soldering challenges and visit us at Booth 1127.

Can't make it to San Diego?  Call or email us and we can help you anytime!

Carol Gowans

February 2013

前段时间我们接触了“Strategic Selling” 和 “Conceptual Selling”的相关内容。 我觉得Conceptual Selling很值得一听，到现在我还经常翻阅那本书。

Conceptual Selling 主要是以客户的角度出发来想问题，说话和办事。作为许多销售和技术销售人员，我们很容易陷入一个固有的销售模式，在和客户接触时我们讲多过于听，很容易抛出一大堆我们这个产品和服务的优点，特点，为什么客户要用我们之类的 “习惯性销售套词”： 因为每天，对每一个客户，基本上每一次见面，这些套词我们都重复过无数遍，在我们心目中滚瓜烂熟，讲起来滔滔不绝。 但是，这真是客户需要的方案吗？我们先清楚了解客户的真正需求了吗？
 

举个简单的例子，比如说卖焊锡膏，我们一见面就会经常搬出这样的套话：这款最新的很好用的呀，润湿好（good wetting)，应刷性能好(good printting)，空洞低(low voiding),没有“枕头效应”（eliminate Head-in-Pillow), 保证你的产率大大提高......客户听着，甚至点头微笑。其实，2个小时前这个客户刚刚接见了另外一个电子焊接材料供应商，他们的销售说了一模一样的关于他们产品的优点。 但是在客户心中，最关心的都不是这些，其实这些问题客户都没有.   最近客户在发愁怎么样改进探针的ICT测试，因为客户发现探针测试的时间最长，是生产的瓶颈(bottle neck)。 如何减少探针测试时间，缩短生产周期cycle time，才是最关键的。客户最想知道的是，究竟是要换一款软一点焊接残留物的锡膏(soft residue solder paste), 让探针好刺穿呢，还是请ICT的设备商来，换探针头和调试一下机器。 如果能大大缩短cycle time, 客户就可以为公司解决一个大问题，就可以得到他老板的赏识，甚至是升职和更多的奖金......

另外有一家供应商来了。这家供应商没有急于向客户“推销产品”，而是先问客户具体的问题，耐心倾听，清清楚楚了解到客户想达到什么效果后，再看看自己有没有适合的产品和解决方案。这家聪明的供应商向客户提供了一款soft residue的锡膏，并且和客户的ICT设备供应商联手，解决了客户ICT测试时间长的问题。结果是，这家供应商拿到了客户所有的焊锡膏订单；而客户因为给自己的公司带来了“巨大的价值”，得到了老板的认可，加薪升职，过年带自己的全家人去旅行了；这家公司也以shorten SMT mfg cycle time而赢得了更过的生意。当然，焊接材料供应商也有更多的来自这家公司的订单，甚至这家公司还向别的公司推荐这个供应商。这是真正双赢的结局。
 

Cheers!
 

Pic: Google Image


 

Folks,

Everyday, we are exposed to the results of surveys and polls.  A typical example might be that President Obama is leading Mitt Romney in a poll by 48% to 45%, but the results are not statistically significant.  A reasonable question might be, “What does it mean to be statistically significant ?”  

To determine statistical significance, typically, the statistician will use the criteria that if there is only a 5 percent or less chance that the conclusion would be wrong, it is considered statistically significant.  So, when another poll would state that President Obama leads by 49% to 44% and it is statistically significant, there is, statistically, less than a 5 % chance that the conclusion is wrong.  The 5 % criteria is not cast in concrete. Sometimes 10%, 1%, or even 0.1% might be used.  However, tradition has given us 5% as the default value for “statistically significance.”  It is also helpful to understand that, the more data points in the sample, the more likely the results will be statistically significant.

But if some data are statistically significant, is it always "practically" significant?  As an example, let’s say that you really like chocolate.  Your favorite brand is in a taste test and it scores 9.6 out of 10, whereas a new chocolate scores 9.7/10 and the results are statistically significant.  On the downside, the new chocolate costs 5 times as much.  Is it worth the extra money to convert to the new chocolate? In this case, we have to ask, is the difference practically significant.  The answer is, in all likelihood, no.  Such a difference as 0.1 point out of 10 is very small, and taste is also subjective.  Here, the result might not be practically significant.  The subjectiveness of a taste test may mean that you either can’t tell the difference or that you still like your favorite chocolate the best.

Let’s consider another less subjective example.  Suppose that, in a certain application, solder voiding  is a critical concern.  So, you measure the voiding of two solder pastes.  After collecting hundreds of data points, you find that the average voiding of one solder paste is 8% and that of the other is 7%.  Analysis with Mintab® software tells you that the difference is statistically significant.  But is the difference practically significant?  Probably not. 

How do you determine practical significance? Typically it would be by experimentation or in some cases by experience.  In our example of solder voiding, suppose experiments showed that, as long as the voiding average is below 30%, there will be no concerns.  In light of this, engineering may have set a specification that voiding must not be greater than 25% on average.  (All of this discussion assumes that the spread or standard deviation of the data is not large, but this subject is the topic of another discussion.)  So, in this case, the difference between 7 and 8 percent voiding may be statistically significant, but not practically significant.  So, a prudent engineer may select the 8% paste if it had other desirable features, such as better response to pause, or resistance to graping, or improved head-in-pillow defect.

So always ask yourself, is the difference both statistical and practical.

The image shows solder joint graping, which is often more of a concern than voiding.

Cheers,

Dr. Ron

Folks,

There is a lot of interest in cleaning PCBs that have been assembled with no-clean solder pastes. 

Recently I discussed the topic with my good friend Mike Bixenman of Kyzen.

Dr. Ron (DR)

Mike, many of the best performing lead-free and lead containing solder pastes today are no-cleans.  They have been designed to solve assembly problems like graping and the head-in-pillow defect.  For the vast majority of applications, the small amount of residue left by a no-clean is not a problem.  However, some assemblers want the performance of no-cleans, but need to clean the no-clean residue as they have extreme reliability or cosmetic requirements.  Are there cleaning solutions for these situations?

Mike Bixenman (MB)

Absolutely!

DR

Can you tell use a little bit about these cleaning solutions?

MB

Several factors come into consideration when engineering electronics assembly cleaning agents. Design factors include the soil make-up, heat exposure, Z-axis clearance under bottom termination components, material compatibility, and cleaning equipment. Typical process goals require that all flux be removed in one cleaning cycle, shiny solder joints (no chemical attack to the alloy), fast production speed, no material effect to labels and other materials of construction, long chemistry bath life, and low operating concentrations.  

Cleaning solutions vary depending on the cleaning equipment. For solvent systems, a solvent cleaning agent is needed - with properties that allow for non-flammability, constant boiling mixture, and being environmentally-friendly to workers and the environment. For solvent cleaning agents that are rinsed with water, the cleaning agent requires a solvent mixture that can be rinsed with water while matching up to the soil and cleaning equipment. For aqueous cleaning agents, the cleaning agent is engineered with properties that provide solvency for the soil, polarity for inducing a dipole and/ or to oxidize and reduce the soil, low surface tension to reduce the wetting angle, buffers to stabilize pH, defoaming to reduce the tendency to foam at high pressures, and inhibitors to widen the passivation range on metallic alloys.

The property most critical is the nature of the soil. As soldering temperatures rise and the time exposed to higher temperatures increase, solder paste material supplies must improve the oxygen barrier and prevent flux burn out. This requires higher molecular weight compositions that may change the nature of the soil and the cleaning solution needed to remove the soil. Other factors such as processing conditions and how these conditions can change the soil’s cleaning properties must be considered. For example, excessive exposure to heat may polymerize the flux residue rending the soil uncleanable. To better understand and plan for these factors, solubility testing and matching the cleaning agent to the soil assist formulators in designing cleaning agents that are effective on a wide range of soldering material residues.

DR

What type of equipment is typically needed?

MB

Two key factors must be matched to clean:

1: Potential energy of the cleaning agent for the soil and

2: Kinetic energy of cleaning machine for delivering the cleaning agent to the soil necessary to create a flow channel needed to rapidly displace the soil.  

The cleaning machine requires energy to deliver the cleaning fluid across a distance and create enough force to deflect fluids under the Z-Axis. The capillary attraction for moving the cleaning fluid into an out of tight gaps is created by fluid flow, spray impingement pressure and surface tension effects. When cleaning under tight standoffs, cleaning agents that wet (form small droplets) improves capillary action, penetration and wetting of the residue. The solubility rate is dependent on the soil, temperature effects and concentration of the cleaning agent needed to dissolve the soil. Hard soils clean at a slower rate and remove the soil in a concentric (tunneling effect) manner. Soft soils clean at a fast rate and remove the soil in a channeling (multiple tunnels) effect.

The Z-Axis gap height has a direct correlation to the energy required to penetrate and remove the soil under components, time required to clean the soil and wash temperature. The irony is that lower Z-axis gaps increase capillary action of the flux for underfilling the bottom side of the component. When this occurs, flux residue dams up and closes any flow channels under the component. Research findings indicate that high pressure coherent spray jets are needed since energy drop is less and defective energy is higher. The wash time needed to clean under a 1-2 mil gap as compared to a 4-6 mil gap can range from 4-8 times longer. Higher wash temperatures increase the softening effect and aid in penetrating and removing the soil. The net effect is that, as components decrease in size, the Z-Axis gap height reduces and the cleaning factors needed to clean the soil increase. These effects favor spray-in-air cleaning equipment over immersion cleaning equipment.

DR

How are the results of cleaning assessed, so that we know that the boards are truly clean?

MB

The first level that we judge cleaning performance by is the visual presence of the residue post cleaning. Most cleaning processes have no problem with removing surface residue from the assembly. The issue is the residue under the bottom side of the component. This complicates the issue since the residue under a specific component is where most failures occur. These site-specific failures may reduce the confidence in existing IPC standards that correlate anion and cation ionic residues over the entire board surface area. So, when designing the cleaning process, we use test cards with bottom termination components and judge cleaning performance by the level of flux residue remaining under those components. To achieve this value, all components are removed and the surface area of the residue under components is graded and statistically analyzed.

Let me finish by adding that highly dense interconnects assembled onto circuit boards is advancing at a rapid pace. Traditional SMT component spacing between conductors was larger. No-clean post soldering residues posed minimal risks to reliability. The information age has spoiled us in expecting higher functionality in smaller spaces. As assembles reduce in size and increase the levels of functionality, cleaning becomes more important.  I hope that the cleaning factors discussed in this interview provide insight into cleaning process design considerations that may be of help.

DR

Mike, thanks.  Who should folks contact if they would like more information on cleaning boards assembled with no-clean solder pastes.

MB

Thanks for letting me share with your readers.   I would be glad to help anyone with the cleaning challenges they face.  Contact me at mikeb@kyzen.com.

Cheers,

Dr. Ron 

Folks,

I’m taking a few moments from Wassail Weekend , held annually in my village, Woodstock VT, “The prettiest small town in America”, to write a post about last week’s workshops at ACI.

Indium colleague Ed Briggs and I gave a 3 hour presentation on “Lead-Free Assembly for High Yields and Reliability.” I think Ed’s analysis of “graping” and the “head-in-pillow” defect is the best around. 

There was quite a bit of discussion on the challenges faced by solder paste flux in the new world of lead-free solder paste and miniaturized components (i.e. very small solder paste deposits.) One of the hottest topics was nitrogen and lead-free SMT assembly. There seemed to be uniform agreement that solder paste users should be able to demand that their lead-free solder paste perform well with any PWB pad finish (e.g. OSP Immersion silver, electroless nickel gold, etc.) without the use of nitrogen. Not only does using nitrogen cost money, but it will usually make tombstoning worse. However, in the opinion of most people, nitrogen is a must for wave soldering and, since it minimizes dross development, it likely pays for itself.

After Ed and I finished, Fred Dimock, of BTU, gave one of the best talks I have ever experienced on reflow soldering. He discussed thermal profiling in detail, including the importance of assuring that thermocouples are not oxidized (when oxidized they lose accuracy). He also discussed a reflow oven design that minimizes temperature overshoot during heating, and undershoot when the heater is off. Understanding these topics is critical with the tight temperature control that many lead-free assemblers face.

Fred Verdi of ACI finished the meeting with an excellent presentation on “Pb-free Electronics for Aerospace and Defense.” Fred’s talk discussed the work that went into the “Manhattan Project.” A free download of the entire project report is available.

There appears to be agreement that acceptable lead-free reliability has been established for consumer products with lifetimes of 5 years or so, but not for military/aerospace electronics where lifetimes can be up to 40 years in harsh service conditions. These vast product lifetime and consequences of failure differences are depicted in the Fred's chart (above). Commercial products are in quadrant A and military/aerospace products in quadrant D.

One of the greatest risks faced by quadrant D products is tin whiskers. Fred spent quite a bit of time discussing this interesting phenomenon. One of the challenges of this risk is that there is no way to accelerate it, so you can’t do an equivalent test to accelerated thermal cycling or drop shock. Fred mentioned that there have now been verified tin whisker fails, the Toyota accelerator mechanism being a confirmed one.

In addition to tin whiskers, lead-free reliability for quadrant D products (with a service life of up to 40 years) in thermal cycle and other areas remains a concern.  I mention that tin pest was not on the list of issues for this quadrant.

Fred and the Manhattan Project Team have identified many "gaps" that need to be addressed to determine and mitigate the risk of lead-free assembly for quadrant D products.  They plan to start this approximately $100M program in 2013.

For those that missed this free workshop, ACI host Mike Prestoy is planning another one in 6 months.

Cheers,

Dr. Ron

Folks,

Let's look in on Patty......

Patty was just finishing a report on work that she and Pete had performed with a team of her ACME colleagues  on reducing the Head-in-Pillow (HIP) defect at a plant in Minnesota. HIP can be caused by printed circuit board and/or a BGA warping during reflow, and, occasionally, by poor wetting BGA solder balls. Fortunately, this case of HIP was due to just a little warping, so replacing the solder paste with one of the new formulations that was designed to minimize HIP had done the trick. Ten thousand boards were produced with no detectable HIP defects.

As Patty wrote the last sentence in the report, she gazed out the window at the dusting of snow that had fallen. She liked living in southern New Hampshire and was thrilled with the house that she and Rob had purchased six months ago in Exeter.  She had to admit that Phillips Exeter Academy was also a draw. She hoped her 18 month old sons, Michael and Peter, would attend high school there, when the time came.

Patty was jarred from these thoughts by the ringing of her phone. She looked at the caller ID and saw that it was Mike Madigan, the CEO of all of ACME. Her stomach tied up in a knot. Sam, her boss, had alluded to the fact that senior management wanted to make her a VP. He asked if she had any requirements to accept such an offer. She said that she wanted to stay located where she was and she wanted Pete to be on her staff. Still, she was a bit nervous about such a big change.

“Patty Coleman, how may I help you?” Patty answered.

“Coleman, this is Mike Madigan. Congratulations, you are our new VP of Technology and Productivity. You will report to me, but, since you are staying in New Hampshire, I want you to report dotted line to Sam for day-to-day things. Coleman, don’t let me down. You are the youngest VP in the history of ACME by 5 years,” Madigan said.

Patty was a little put off by his gruff manner, but had been told to expect it.

“Thank you Mister Madigan, I’ll do my best,” Patty responded.

“I already have an assignment for you,” Madigan went on.

“You have done great things by improving line uptime at many of our sites, and profitability is up everywhere, but I sense we are still missing something. Do you know why?” he asked.

“Because the correlation between profitability and uptime is not as strong as one would like?” Patty asked.

“Coleman, I’m already glad I promoted you! That is exactly my concern.   Explore the situation, fix it and give me a better metric. I want all sites to use this new metric so I will know which locations to focus on. I want a status report in 3 weeks.” Madigan finished.

“I'll get right on it Mister Madigan and will have an update in 3 weeks or sooner,” Patty answered, exhilarated, but a little shaky.

“Good! Oh and Patty, call me Mike. It’s not the 1960s you know,” he chuckled as he hung up.

Patty hung the phone up feeling happy and stressed. She was glad to get the promotion, but knew she had to deliver.

Patty had thought about this productivity metric concern in the past. She knew where to start, she would call The Professor. She was surprised when he picked up on the first ring.

“Patty, it’s great to hear from you. How are Rob and the boys? We expect to see your sons here at Ivy University as students in 16 years,” The Professor chuckled.

After exchanging a few more pleasantries and sharing the news about her promotion, Patty got right to the point.  

“Professor, I need a metric that measures total productivity in electronics assembly. Uptime is a great metric, but it doesn’t correlate one-to-one to profitability,” Patty explained.

Patty expressed her surprise that no metric for total productivity was in wide use. They discussed the issue for a few more moments and then The Professor had a recommendation. “Read the NEMI (National Electronics Manufacturing Initiative) 1998 and the iNEMI 2011  Technology Roadmaps. Focus on board assembly and I think you will find your answer,” The Professor suggested.

After a few more pleasantries, The Professor had a request.

“Patty, I am getting a little award in Washington, DC. I have room for two guests at the award presentation. I was hoping you and Rob would come,” The Professor requested.

Patty said she would check their schedules, but was sure it would work out. She was honored that he thought so much of her and Rob.

As she hung up the phone, she went to ACME’s Tech Library in search of the iNEMI roadmaps. She quickly found the 1998 NEMI Technology Roadmap, but unfortunately only a summary of the 2011 iNEMI Roadmap was available. She thought she would read the 2011 Roadmap summary first. It was overwhelmingly impressive in its coverage of technology, at the wafer, chip, component, and board levels. The thoughtful inputs of over 575 participants, from over 310 organizations, were clearly evident. All of the current and emerging technologies were presented in detail.

“What a treasure of information,” Patty thought.

But she didn’t see an answer to her question.

So she went to the “Board Assembly” section of the 1998 Roadmap and in a few minutes she saw the answer: Board Assembly Conversion Cost in cents/I/O.

“What a simple concept,” she thought.

As she studied the document it became clear that about 30% of it focused on reducing conversion costs. Conversion costs were defined as all of the cost of assembly minus materials cost. To give this metric meaning, to enable comparisons between different manufacturing sites, the total amount of conversion cost for a manufacturing site was divided by the total number of input/output (I/O) terminals (i.e. component leads) assembled.

“This makes sense,” she thought. “You add up all of the non-material costs of assembly and divide by all of the leads you assemble. This metric shows how efficiently you assemble each lead.”

It then dawned on her that she had seen a metric like this before. She saw the notebook from The Professor’s workshop on Cost Estimating in her bookcase.  She grabbed it and flipped through it. There it was: non material assembly cost per I/O (NMACIO).

The great mystery to her is why the folks at NEMI didn't emphasize these types of cost performance metrics in newer roadmaps.

Example:

Figure 1: Example shown Indium8.9 flux with SAC lead-free alloy

The reason for approaching this subject is that often there has been some confusion in regards to the difference between max slope (a category reported on most profiling software) and the ramp rate listed on a data sheet.
























Figure 2: Max Slope

The max slope is very often attained in the first zone as the PCB moves from ambient temperature into the oven. In most cases the oven zone setting for the first zone is 100°C or better. The change in temperature between ambient and the first zone then is a minimum of 75°C (assuming 25°C as ambient) and so it’s easy to see that the greatest change in temperature (max slope) in most cases is typically found in the first zone

The focus of max slope is more from a component view point, to avoid thermal shock, usually 3°C/s is recommended as the upper limit

Figure 3: Ramp or Average Rate


The ramp rate may be better described as the rate (change in temperature over time) from ambient (room temperature) to peak. And is more practically used in a ramp to spike type profile

From the view point of the solder paste, the lower the ramp rate the better, usually 1-2°C/s. This is to drive off volatiles and help minimize solder defects such as solder balling, solder beading, and tombstoning. This rate becomes even more important as the solder paste deposit continually decreases in size, as we move to 0201’s and smaller discrete components and from 0.5mm pitch area array packages to 0.4mm and smaller. Due to this miniaturization, the observance of graping and head-in-pillow have become more common. The reflow process window is becoming very narrow and this attribute (ramp rate) has become as important as time above liquidus and peak temperature.

I'd love to discuss this with you, if this topic is affecting your SMT process. If you'd like, feel free to contact me.

Folks,

I thought I would take a stab at listing the minuses, pluses, and “it’s a wash” aspects of assembling with lead-free (LF) solder. Here are my first thoughts. Please tell me what I missed or disagree.

Cheers,

Dr. Ron

Minuses

1.    Pb-Free requires higher reflow temperatures
The Tm for LF solders, in the 217-229C range, has created numerous challenges:

a.      PWB warpage and damage

b.      Component damage

c.      New defect modes such as graping and head-in-pillow defects (although concurrent reduction in solder paste deposit sizes for 0201 and 01005 passives and 0.3 mm CSPs also exacerbate these defects)

d.      Defects related to increased oxidation

e.      Increases in voiding

f.       Increases in tombstoning

2.      The higher cost of LF solder, mostly for wave soldering

a.      It’s not just the silver, tin is much more expensive than lead

3.      Poorer wetting of LF solders, creating the most significant challenges in wave soldering

4.      More rapid copper pad dissolution on PWBs in wave soldering

5.      LF solder attack of wave solder machine components

6.      LF reliability in harsh thermal cycle testing appears poorer than tin-lead solders

7.      Tin Whiskers

It’s a Wash

1.      Short-term reliability in consumer product-type environments

2.      Protection of the environment if discarded products are improperly disposed of

a.      Lead in electronics has never been shown to cause a problem in land fills

3.      Since July 2006, about $3 trillion of products have been manufactured with LF solder, with no “the sky is falling”-type of problems

Pluses

1.      LF solder's poor wetting enables finer lead spacings (see photo Courtesy of Motorola)

a.      It may be argued that some modern electronic products (e.g. smartphones) could not be made with tin-lead solder

2.      It is safer to recycle LF solders, especially if performed in a non-controlled environment

在上周行业的SMTAI盛会中，Indium公司有好几位同事被PCB007采访。

首先是李宁成博士(Dr. Ning-Cheng Lee)被采访。他在采访中简述了Head-in-Pillow缺陷和针对此的几种几种检测方法。 李博士和其他几位作者合写的论文，可以在此下载。http://realtimewith.com/pages/rtwvprofile.cgi?rtwvcatid=1&rtwvid=1577

接下来是Dr. Ron Lasky简述了他对这四年来实行RoHS的感悟和见解。
http://realtimewith.com/pages/rtwvprofile.cgi?rtwvcatid=1&rtwvid=1576

Tim Jensen作为Indium公司PCB焊接材料的产品经理，也和大家分享了他对PCB组装焊接材料的一些看法。http://realtimewith.com/pages/rtwvprofile.cgi?rtwvcatid=11&rtwvid=1584

Dr. Ron Lasky再次被采访，和大家共享了他研究领域之一：在电子组装中提高产率(productivity)http://realtimewith.com/pages/rtwvprofile.cgi?rtwvcatid=11&rtwvid=1605

最后，最激动人心的是Indium公司荣获了今年SMTA Corporate Award (公司奖)
！http://realtimewith.com/pages/rtwvprofile.cgi?rtwvcatid=6&rtwvid=1614

Cheers!

Video links & Pics: Realtimewith.com

• Oxidation Barrie能夠大大減少，甚至完全消除枕窩效應(Head-in-Pillow defect). 枕窩效應是因爲BGA球和solder paste在回流前的preheat or soak time階段分開了，在熔融過程中，表面被氧化；儅BGA球和paste再次接觸時，表面被氧化層太厚了，所以整個焊點沒有完全融合好。如果有良好的Oxidation Barrier, 那麽能大大減少BGA球或是paste在熔融過程中因爲分開而被氧化。
   
• Oxidation Barrie 能夠提高精密元器件，小開口印刷的焊點的結合。小開口的下錫中，4號錫粉的表面積(powders’ surface area)其實是比3號粉增加了，但是助焊劑(paste flux)沒怎麽增加，那麽在焊接過程中，有些錫粉表面的氧化物可能就沒有被完全清洗乾淨。被氧化的錫粉不能和整個焊點完全融合，形成良好的焊接點；而是在焊點附近出現一串像葡萄一樣的小珠子，我們也叫做graping defect。 有了好的Oxidation Barrier, 就能夠更有效地預防graping defect, 提高小開孔印刷焊點的融合。
   
• Oxidation Barrie能夠減少留在電路板上的活化劑activator，增強電性能的可靠性。Oxidation Barrie 能夠防止焊接表面被氧化，activator是清洗表面被氧化的部分。如果有了良好的Oxidation Barrier，那麽activator 就可以相對減少。回流后留在電路板上的activator 也少了，那麽也減少short cut 等現象，提到電性能可靠性。
   

Cheers!

Pic: Indium Corporation

Folks,

The adventures of Patty and Rob continue.......

Rob bolted upright in bed. He had that terrible feeling that he had overslept for an important appointment. His eyes quickly found the clock and it said 10:30! 

“Wait a minute!” he thought, “It’s Sunday.”

He looked a Patty peacefully sleeping and decided to let her sleep. They had had a tough two months. Ever since they proposed increasing uptime to greater than 60% on two “experimental lines”, they were working 90 hour weeks. They just felt they needed to constantly monitor two lines, to assure that things were going smoothly. They felt satisfaction that they achieved 68.8% uptime in a two month period, compared to the company average 30.4%, which is still very good.

The local newspaper got word of this effort and did a story on Rob and Patty’s work. The article was well written and very complimentary to both he and Patty, as well as ACME. Sam Watkins, the site general manager, was very pleased with the good PR. The accompanying photos were really nice too.

The big shocker came this past Tuesday. “Sixty Minutes” called and said they wanted to do a segment on “The US Competing with the Far East in Electronics Manufacturing.” In agreeing to be interviewed, Rob and Patty insisted that members of their ACME team be included. In addition, they felt it was only fair to include the efforts of Rita from their stencil printer and reflow oven supplier and States, their colleague from the component placement company. And they couldn’t forget Eric, from ACME’s prime solder paste supplier. These three folks helped Rob and Patty and their team to develop the plan to achieve the 60+% uptime.

An even bigger shocker came when the Sixty Minutes crew told them that Andy Grove would be in the segment because of his recent article in Business Week, How America Can Create Jobs

 Grove insisted that to participate in the piece, he wanted to visit ACME to see what Rob and Patty were doing. So the Sixty Minutes crew was visiting ACME’s plant this week as were Rita, States, Eric and now “Andy.”

“Maybe we should call him Mr. Grove,” Rob thought.

Rob had suggested that he and Patty go to Berdick’s in nearby Walpole, NH for Sunday brunch and then to play golf. Rob had to chuckle, it was mid July and he and Patty had played golf 27 times (she kept a spreadsheet), he had beaten her 14 times and she was miffed. Even during their 90 hour weeks they would take a break 3 times a week to play 9 holes.

On Monday they were meeting with site GM, Sam Watkins, to discuss what they would tell Sixty Minutes.

Rob and Patty’s Sunday was delightful. The brunch was delicious and relaxing and they both played golf well, Patty’s 68 beating Rob’s 69.

It seemed like no time at all and Rob and Patty were in Sam’s office.

“Just assure me that this Sixty Minutes thing is not some expose that will embarrass ACME or put me in jail,” he teased.

Patty took the lead and explained what they had done. They trained the operators on the importance of line uptime, they worked with Rita, States, and Eric to develop a plan to assure that there would be minimum unscheduled downtime. They had to order extra spare parts and solder paste to assure no stoppages due to parts or paste shortages. One obvious thing is that they would be using two times or more the normal amount of solder paste. The two lines in the high uptime experiment had an average of one change over per day, consistent with ACME’s business.

They also increased routine maintenance on all machines. Both this maintenance and added spares was an increased cost, but these costs were second order effects compared to the dramatic profit increases due to almost 70% uptime.

Preparation for the next three jobs for each line was meticulous, so that setup time was minimized.  Feeder racks were used extensively in minimizing setup time for changeovers. In addition tape splicing was employed to minimize any assist time for component placement. States’ help was crucial in the component placement part of their efforts, Rob pointed out.

Patty went on to describe how Rita helped them in their efforts to develop minimum assist times for the stencil printing process.  The reflow oven presented the least concerns in assist or unscheduled downtime.

The solder paste they selected was robust in that it had a very good response to pause, excellent tack, and minimal slump.  The paste also had the best track record for minimizing defects like Head-in-Pillow and Graping.  Eric also participated as an enthusiastic partner in the effort.

Patty mentioned that their colleague, Phil, had agreed to monitor uptime for two standard lines during the two month trial to compare downtime metrics to the high uptime experiment. These would be experimental “controls.”

She then showed the uptime data for the two high uptime lines and Phil’s control lines. The control lines had ACME’s respectable 30% uptime, but the high uptime lines had almost 70% uptime. Rob went on to explain all of the things the team did to minimize downtime, most of it was common sense. Sam was especially interested in one downtime category.

“What is floundering time?" Sam asked.

 “That is time when the line is not operating due to some unplanned error,” Rob answered.

“Can you give an example?” asked Sam.

“Sure, you know how we have a quite organized approach to setups?” Rob responded.

“You mean our use of white boards to write down all of the things needed for the next 3 jobs on each line?” Sam came back.

“Yes, that is one of our biggest sources of floundering time,” Rob replied. He went on, “Someone will write that they have the stencil for the next job, when they just think they know where it is. When it comes time for that job the stencil cannot be found and an hour is lost.”

“Phil also noted a case where a job was finished on a line at 11:15AM, since lunch was at 12 noon, the changeover for the new job was not started until after lunch. Forty five minutes was lost, forever,” Patty added.

Sam gulped.

“So we are losing more than 25% uptime to ‘floundering?’” Sam weakly asked.

“According to the Professor, it’s endemic in the industry,” Patty interjected. “He coined the term, ‘Floundering time’,” she went on.

Sam then mentioned how the “bean counters” at ACME we really impressed with the two high uptime lines. ACME’s CEO wants a concerted effort to transition all of ACME’s assembly lines in North America  to higher uptime performance. Manufacturing in North America would also mean no 2-4 weeks of transportation time from the Far East. Patty, Rob, and their “team” were to form a new group in ACME to do this. Patty would be the Director of the group.

As the meeting was about to close, Sam asked what surprises Patty and Rob had during this experiment.

Rob then shared, “It relates to floundering time.   We found that even among the engineers, no one appreciated the value of one hour of production time. We asked a group of operators what an hour of production was worth and the figures ranged from $50 to $500 dollars. ACME runs two shifts at 30% uptime, that’s about 1500 hrs per year. Our typical line produces $30 million per year, that’s $20,000 per production hour. When we told the operators this, floundering time dropped significantly.”

Patty added, “The other thing we saw is that a “watchdog” is needed. If someone isn’t constantly watching things, floundering and assist times will go up. Since productivity is doubled with a high uptime line, the added cost of a watchdog is insignificant.”

Epilogue: The Sixty Minutes Segment was a great success. Patty was made Director of Corporate Productivity, but was also asked to manage Pete, who would take over her old group. No one seemed to worry that Patty was Rob’s boss, except maybe Rob!

Folks,

Patty and Rob return from their honeymoon.......

Patty had just finished some emails and was ready to head off to meet Rob and some of their buddies for lunch. When she and Rob returned from China a month ago, Sam, the site GM, told both of them he was giving them an extra week of vacation for their honeymoon. Their China trip had been an unqualified success in helping the China teams achieve more productivity and higher yields. Sam had received numerous positive reports from the Chinese managers involved. There were several requests to have Patty and Rob stay a year in China to help with the many process issues that the China team has. Fat chance of that happening, Sam needed Patty and Rob here! Sam also mentioned that he knew that the trip was a little stressful coming so close to their wedding, so the extra week was ACME’s gift to the young couple for their sacrifices.

The wedding went off without a hitch. Patty was touched at how choked up her dad was in “giving her away.” The weeding reminded Rob and Patty how close they were to their parents. They both agreed that the support of their parents was crucial in any success that they had in life.

For their honeymoon they decided to tour France, Italy, and Germany. Rob was really proud that he handled the languages a little better than she did. Of all the things that they saw, they were most impressed with Pompeii. Because the city was covered in hot ash in a matter of moments, it was as if Pompeii was frozen in 70AD.  Visiting Pompeii was like stepping back into the time of the Caesars.

Truth be told, Patty was happy things were back to “normal.” It was pleasant to have their working schedule and to go home to their apartment at night. A couple nights a week, and most Saturdays and Sundays, she and Rob played golf. He had improved somewhat and she was a little annoyed that so far this year he had beaten her more than half of the time….and yes, he was rubbing it in.

As Patty approached the cafeteria she heard a friendly but heated discussion.

“No way can you evaluate an assembly company with just 10 questions,” Phil Anderson stated emphatically.

“I’m really convinced we can, I’ve thought it through a lot,” responded Rob.

“What’s the spirited debate about?" asked Patty as she sat down.

“Rob thinks you can evaluate an assembly company by asking a lead process engineer only 10 questions. Phil thinks he’s nuts,” responded Patty’s best friend Jan Curtis.

“I’ve thought about this quite a bit,” said Rob. “I’ve just finished reading Malcolm Gladwell’s ‘Blink.’”  “Gladwell claims that often the best judgments can be made quickly with just a sampling of data,” Rob went on.

“Be specific,” challenged Phil.

“OK, I actually developed 10 proposed questions to evaluate a assembler, let me list them and then defend them. Maybe you guys have better ones,” said Rob. 

Patty thought, as she heard this, that it was good news that ACME was looking to buy more assembly companies to handle their ever increasing workload……not like AJAX that was laying folks off.

Rob had come prepared, he actually had some print outs. His ten questions were:

1.      What is the composition of SAC305?

2.      What are tin whiskers?

3.      In a stencil aperture, what is the area ratio?

4.      What is an approximate peak temperature for a reflow oven in lead-free assembly?

5.      A board is inspected after wave soldering and one lead is not soldered to the board. The board is run through the wave solder machine again and has the same defect on the same lead. What is the most likely cause of the defect?

a.       The solder temperature is too low.

b.      The pad on the board is oxidized.

c.       The preheat temperature is too high.

6.       What are local fiducials on a PWB for?

7.       What does thixotropic mean in regard to solder pastes?

8.       A chip shooter places passives at a rate of 36,000 per hour. It is placing 300 passives on a PWB, how many seconds will the chipshooter take to place the passives on one board?

9.       A reflow oven belt speed is 100 cm/min. The PWB is 40 cm long. What is the minimum cycle time that the oven can support?

10.   What is tombstoning?

“You have got to be kidding,” shouted Phil, “everyone will score 100% on that test.”

Jan chimed in, “I’m not so sure. We hang around people all day who study this stuff. I’m not sure the typical process ‘engineers’ have enough time to study and learn new things…..Remember the 'water in the solder' and the 'isopropyl in solder paste' incidents?”

At this comment, Phil spit up his ice tea and started choking from laughter. One of their friends, Sally Herman, had been sent to a recently acquired company to help them with assembly process issues. One of the “process engineers” introduced himself by bragging that he was saving the company money by taking used, dried solder paste and mixing it with isopropyl alcohol so that the paste could be used again. Later in the day, the same chap shared that he thought he had a solution to the poor hole fill problem in lead-free wave soldering…….the solder was too thick, if it was mixed with water it would fill the holes better he opined.

Jan added, “As a minimum these questions act as a good screening process.”

Rob interjected, “That’s my point. I’m not saying this tells us everything, but you will agree that if a lead process engineer can’t handle these questions, it is unlikely he or she would be able to solve graping, or the head-in-pillow defect, right?"

All at the table murmured agreement.

“On second thought, maybe you have something here Rob," Phil said. “What do you propose as a passing score," he went on?

“Seventy percent,” Rob answered. 

Are Rob’s questions reasonable to evaluate an electronics assembler? What are the answers? Comment with your answers. Stay tuned to find out.

Cheers,

Dr. Ron

The image above is from: http://en.wikipedia.org/wiki/File:Blinkgla.jpg

Folks,

Tin Whiskers (TW) continue to generate considerable interest. People often suggest that their risk is great and yet unknowable. RPN may help to clarify the TW risk. What is RPN? It is the risk priority number from failure mode and effect analysis.  As this link tells us:

A failure modes and effects analysis (FMEA), is a procedure in product development and operations management for analysis of potential failure modes within a system for classification by the severity and likelihood of the failures. A successful FMEA activity helps a team to identify potential failure modes based on past experience with similar products or processes, enabling the team to design those failures out of the system with the minimum of effort and resource expenditure, thereby reducing development time and costs. It is widely used in manufacturing industries in various phases of the product life cycle and is now increasingly finding use in the service industry.

RPN is an important part of FMEA. It is the product of three numbers that range from 1 to 10. The first number is the severity (S) of a possible fail. A “10” would be given if the failure injured someone, “7” would be assigned if the failure caused a high degree of customer dissatisfaction, whereas a “2” would be given if the failure has only minor negative effects.

The second number is occurrence (O) of a fail. The highest rating is a “10,” which would be a failure every day (reminds me of Windows ME!) or one fail in 3 events, whereas a “7” would be a failure every month or one in 100 events. A “2” is a six sigma fail rate.

The last number is detection (D) of a potential fail. A”10” would suggest that the detection of a potential fail is either not performed or not possible. A “7” is a manual detection approach that may not be reliable, whereas a “2” is 100% effective potential failure inspection.

So obviously a product with a RPN of 10x10x10 = 1000 is a disaster, its failure is dangerous, frequent and incapable of being detected beforehand. Industry rules of thumb suggest that and RPN of 200 needs to be addressed and an RPN of 75 is usually considered acceptable.

Let’s look at a “ball park” RPN for tin whiskers (TW). We will assume the application is a critical IC in a PC.  Let’s assume that a severity rating of “S” of 8 (failure renders the unit unfit for use) is reasonable. TW are hard to inspect for future fails, so detection, “D,” could be as high as a 10. At this point we are at 8 times 10 equals 80 for both. A bad start.

Occurrence , “O” for TW failure modes is dramatically different. When trying to assess the occurrence of TW fails, one is often directed to NASA’s web page . Many reference this web site that lists a little more than a score of TW fails. What escapes me is that people don’t seem to appreciate the rarity of less than 100 fails in decades of data collection. Surely TW fails are not common. I could find no report of a failure of a RoHS compliant product anywhere on the internet. So it would be hard to rate “O” any higher than a “2.” I suspect that the reason few TW fails have apparently occurred is due to TW mitigation techniques that are widely practiced.

I would expect that “modern” process defects like the head-in-pillow or graping defects could have a much higher RPN than TW, if assembled without proper process controls and materials. However, there is little need to worry about these defects either, if you use the right solder paste and practice some assembly process precautions.

Patty, Rob, and The Professor finished their tasks in Shenzen and were flying to Shanghai for their last set of challenges in electronics assembly.  Then they would head back to the US, Rob and Patty being only a week away from their wedding day.

As usual Rob, conked out as soon as the plane lifted off. Surprisingly, The Professor also drifted off to sleep. Patty was too excited to sleep. Rob’s mother had given her and Rob their wedding presents early … an iPad  for each. They decided to bring only one laptop and one iPad. Patty was a little nervous about using the iPad for presentations but it worked quite well. She was still surprised that the iPad did not have a USB port. The Professor also gave each of them an early wedding present, a Pickett slide rule for Rob and a K&E slide rule for her. She must be the only person in the world right now that was watching a movie on an iPad and solving a math problem with a slide rule!

True to form, The Professor was passionate about how learning to use a slide rule helped improve a person's innate math ability. He showed Patty and Rob how to use them and gave them several assignments. Rob was better with his slide rule than Patty due to the amount of “one on one” time he had with The Professor. She had to admit that using the “slip stick” gave one more of a feel for calculations and it was consistent with one of The Professor’s adages: “Always know approximately what the answer to a calculation should be…..it will help you to avoid errors."

In addition to the iPad and slide rule, Patty was excited to be going to Shanghai at the time of the World Expo 2010. Our trio had scheduled some time at the expo into their busy schedule.

Their plan was for Rob and The Professor to work on some productivity issues and for Patty to take on some of the process materials related problems. The three of them again met with the site GM for ACME’s newly acquired plant in Shanghai, a Mr. Wong. Wong was relieved to find that they all spoke Mandarin, as his English was a little rough. When The Professor addressed him in excellent Shanghainese, everyone was speechless. Patty was determined to ask him about this later. No American spoke Mandarin, Cantonese, and Shanghainese!

They again agreed to stick to Mandarin. Patty headed out to the line, accompanied by a young Chinese engineer, Zhou Chang, who seemed to be taking more interest in her than expected. She tried to make her engagement ring visible, but she wasn’t sure the he knew of the significance of it. When she got to the line that was experiencing yield problems, the Engineering Manager, Fei Ding, met her. He showed her some of the fails and she quickly identified the head-in-pillow (HIP) defect as the likely culprit. After investigating some more fails, looking at stencil printing, some of the BGA components, and component placement, she asked Zhou Chang what spec was used to thermal profile the line.

“I don’t understand what you mean,” Zhou said in Mandarin.

“How do you determine what the reflow profile should be?”  Patty responded.

With more discussion, Patty determined that they had one profile for all products! Fortunately most of the products were of similar, small thermal mass.

“What solder paste do you use for this line?", Patty asked.

The embarrassed silence suggested that Zhou did not know! They grabbed a tube and Patty was relieved to see that it was one of her favor solder pastes. Since profiling was so rarely performed, Patty and Zhou had to go to another part of the complex almost a mile away to find a reflow profiling unit. After taking the profile, the likely solution appeared. The 11 zone oven was very long and the reflow profile had a long thermal  “soak” before the temperature went above liquidus. This long soak probably exhausted the flux, so that when the PWB went above liquidus, there was little flux left, resulting in oxidation and poor reflow.

All during their time together she had mentioned that her fiancé Rob was here, with her on the trip. This information seemed to do the trick.

“Zhou, why don’t you look up the solder paste spec on the web and then set up the right type reflow profile,” Patty suggested.

It was clear that Zhou was troubled. It became obvious to Patty that Zhou did not know how to profile a reflow oven. Patty set about working with Zhou to accomplish this mission. Within an hour they had re-profiled the oven and, over the next two hours, 300 PCBs were manufactured with the yield improved to 95%.

Patty asked Fei if she could give a brief presentation on the head-in-pillow defect to his team and he cheerfully agreed. Fortunately for Patty, her friend Mario Scalzo had given her his presentation that he gave at APEX 2010 on HIP (head-in-pillow). Patty always enjoyed visiting Mario in Utica, NY, as he always knew the best restaurants in town.

Her major points were:

HIP is caused by the failure of the BGA sphere to reflow with the solder paste. There are 3 major reasons for HIP:

1.       Supplier Issues

a.       Solder BGA sphere oxidation

b.      Silver segregation to the BGA sphere surface

2.       Process Issues

a.       Stencil Printing

                                                               i.      Registration accuracy

                                                             ii.      Insufficient solder paste

b.      Component Placement

                                                               i.      Off pad

                                                             ii.      Out of plane

                                                            iii.      Non optimum pressure

c.       Reflow

                                                               i.      Inappropriate reflow profile

                                                             ii.      Flux exhaustion

                                                            iii.      PWB warpage

3.       Material Issues

a.       Poor solder paste transfer efficiency

b.      Insufficient solder flux oxidation barrier

c.      Solder paste slump

d.      PWB or BGA warpage

Patty went on to say that she had investigated all of these issues with Zhou, and that the reflow profile was not optimum as the very long soak time had exhausted the flux. The other possible issues in the list did not seem to be a concern.

At the end of the day Patty, Rob, and The Professor met at the GM’s office to leave together for dinner and the Expo. Patty had to ask, “Professor, how can you possible know Mandarin, Cantonese, and Shanghainese?”

“Actually I speak Min reasonably well too,” he replied.

“How can this be?", Rob inquired.

“Mother and father were missionaries with Wycliffe Bible Translators,” The Professor answered.

“I grew about around many languages during my youth. Mother and father speak more than I do,” he finished.

Patty went on to tell about the interest that Zhou Chang seemed to have in her, and how she had to discourage him.

“The burdens of being a beautiful young woman,” Rob teased.

Patty elbowed him, but they all left the taxi laughing as they headed for a restaurant near the Expo.

Best Wishes,

Dr. Ron 

The Shanghai, slide rule, and HIP images are from: 

http://pool14.files.wordpress.com/2008/12/shanghai_skyline_g.jpg

http://www.hpmuseum.org/powerlog.jpg

http://ppsimanufacturing.files.wordpress.com/2010/03/bga100.gif

上週在美國的拉斯韋加斯(Las Vegas), IPC舉辦了美國地區行業的盛會APEX.   Indium公司一如既往的在展會中心安排展位，和業界各位舊友新友交流，與大家分享最新的產品和技術，傾聽大家的反饋和聲音。

除此，在人山人海的技術會議交流中心(paper presentation, educational workshop)，Indium公司的五位大將還為大家做了精彩的演講：

• Ning-Cheng Lee, Ph.D, Vice President of Technology 李寧成博士：

²       Lead-Free Flux Technology and Influence on Cleaning.

²       Selection of Dip Transfer Fluxes and Solder Pastes for PoP Assembly.

²       Achieving High Reliability Low-Cost Lead-Free SAC Solder Joints Via Mn or Ce Doping.
 

• Ronald C. Lasky, Ph.D. PE, Senior Technologist

²       Achieving High Reliability for Lead-Free Solder Joints – Materials Consideration

• Mario Scalzo, Senior Technical Support Engineer

²       Addressing the Challenge of Head-in-Pillow Defects in Electronics Assembly.

²       Challenges for Implementing a Halogen-Free Process

• Eric Bastow, Senior Technical Support Engineer

²       Understanding SIR

• Chris Anglin, Applications Development Engineer

²       Stencil Printing Transfer Efficiency of Circular vs. Square Apertures with the Same Solder Paste

 這些文章在Indium的技術網站上面，都可以免費下載。

Cheers!

Folks,

 Bob Landman’s comments to my tin whisker posts appear below. Friendly dialogue such as this helps us to all learn more and is appreciated. Thank you Bob, keep me honest!

However, Bob’s comments do not change my position, which is:

1.     Tin whiskers exist and can cause failures

2.     However, there is yet no data that suggest that there are numerous tin whisker failures, or that a significant reliability risk exists due to tin whiskers in RoHS-compliant products.  NASA's TW website notes only 26 fails.

3.     Although not completely understood, tin whiskers can be created in the lab, and mitigation (not elimination) and reliability test techniques exist and have been demonstrated.

4.    With well over $1 trillion in RoHS-compliant electronics manufactured since the early 2000s, there have been no significant reliability issues as compared to tin-lead solder.

5.     Long term lead-free reliability (> 5yrs) has not been demonstrated. Hence, mission critical products should not use lead-free electronics at this time.

6.     Tin-lead solder does not assure defect-free electronics with perfect reliability.

As I type this post, I am surrounded by more than 20 RoHS-compliant products, some dating from 2005. Outside my office, at Dartmouth’s Thayer School of Engineering, is our computer center. The thousands of RoHS-compliant products that the computer center buys each year (they get me my laptop, etc)  are almost all RoHS-compliant. No unusual reliability issues have been noted.

Bob mentions that CALCE reports that 31% of laptops fail in 3 years. This number actually seems low to me. Upon reading the paper, one finds that over 10% of the 31% is due to accidents. 
A study of 100,000 hard drives at Google suggests that hard drive fails are in the 5% range per year, which may account for much of the 20% of fails in 3 years. But what solid conclusion can be made from these data? Nothing, unless failure analysis is performed.

The sky is not falling. Lead-free has process-ability and reliability challenges, such as graping, head-in-pillow, voiding, etc. With data-driven process optimization at all steps in the manufacturing of the ICs, components and assemblies, good lead-free yield and reliability can be achieved.

Lead-free is here to stay. It is up to us to perform the experiments and develop the techniques to assure that RoHS compliant products have acceptable reliability.

Bob's comments follow:

My source for the dead vehicles that arrive at car dealers having whisker problems, comes from my former professor of physics, Dr. Henning Leidecker at NASA Goddard Space Flight Center in Greenbelt MD.   Dr. Leidecker said that in the last four years his office has been contacted by seven major suppliers of automotive electronics inquiring about failures in their products caused by tin whiskers. He said his office has contacted Toyota offering to help analyze its acceleration problem, but hasn't heard back. For full context, read the rest of the article [http://wtop.com/?nid=108&sid=1898265].

Ron Lasky confirms that parts plated in pure tin will grow tin whiskers "with a certain amount of aging". According to NASA, whiskers can grow in hours, days, weeks, months or years. It depends on at least six factors; the quality of the tin plating, the residual stress in the coating, was the coating annealed or not, grain uniformity, temperature, humidity, and unknown other factors we don’t yet understand which is what makes it so difficult to stop whiskers from growing and is why there are so many papers published on the subject (as you can clearly see at John Barnes website) yet we still do not understand why or how they grow.

So yes, is entirely within the realm of possibility that "new" products have failed due to tin whiskers or perhaps dendritic growth.

NASA cannot tell us who the manufacturers are who reported these events due to confidentiality agreements.  Dr. Leidecker says they get these calls from other industries as well and most request a non-disclosure agreement.  NASA feels it’s better to get some information rather than none, don't you agree?

Last  week at CALCE at UMd. it was reported that 31% of all laptops fail within 3 years. This is the link to the report http://www.squaretrade.com/pages/laptop-reliability-1109/  No information is given as to what has failed. Is it due to whiskers?  We do not know.

What we do know is that the laws of physics have not been repealed.  Tin will most certainly grow whiskers so using leadfree solder and tin plated components has to result in tin whiskers growing.

NASA continues to log failures.  NASA Goddard is now studying the Toyota incidents for NHTSA.  Again, a non-disclosure statement has been signed so they cannot comment on the study at this time.

Dr. David Gilbert of Southern Indiana University has demonstrated that a low resistance or shorted input between the wires from the pedal electronics to the electronics control module will cause Toyotas to open their throttles full.  Perhaps the problem is due to leadfree manufacturing (which Toyota admits it began in 2002-3)?  Perhaps it is software?  We don't yet know but we can be reasonably certain that not all the accidents are caused by the owners of the vehicles.  You can see pictures of the Toyota parts at my website [www.hlinstruments.com//RoHS_articles/Toyota/]   The pedal has a pc board layout that I would have been comfortable with.  In particular, the SOIC part that converts the signals from the Hall effect sensors (that sense pedal position) into 1-5Vdc signals sent to the electronic control module is very close to the edge of the board.  The board has serrated edges which indicates it was snapped out of a large panel of these boards after the parts were soldered to it.  It's possible a trace or lead has fractured or one of the capacitors or resistors.  We know that leadfree solder is more brittle than tin-lead. Perhaps a few boards are marginal and over time a lead opens or becomes intermittent?

The EU was warned that tin whiskers and brittle joints would result if lead was banned from electronic assemblies but went ahead and banned lead from tin-lead solder and platings on parts. They acknowledged the possibility of reduced reliability under intense pressure from hi reliability industries and did exempt some products (military, aerospace, etc...).  What difference did it make since the majority of component manufacturers refused to continue to offer tin-lead plated leads?  That is why NASA replates it's components with tin-lead at Corfin Industries and uses only tin-lead solder.


Bob Landman

http://www.hlinstruments.com//RoHS_articles/Toyota/Toyota%20Dr%20Gilbert%20Preliminary_Report022110.pdf

Patty was checking her email. She noticed a note from someone who had attended last night’s SMTA meeting. Patty had just been elected chapter president, after giving a talk on the head-in-pillow defect. In her talk, she also shared how important it was to work closely with your materials and equipment suppliers. To her, it was obvious that her suppliers were interested in her success. If they were competent, why shouldn’t she rely on them for technical information and help. If she didn’t think they were competent, she should get new suppliers. She was surprised at how much “push back” she got from the attendees. Several people stated that they felt that suppliers where just out to make a sale and that a smart person just bought from the supplier with the cheapest price. Patty thought that this perspective was negative and self destructive. She was sure that 60% of all process knowledge was learned from her suppliers, either in person or at the technical shows like APEX and SMTAI. She felt the main reason to go to these shows was the technical program. And some of the best papers were presented by the better equipment and materials suppliers. 

One of their marketing VPs even told her, “We believe that the more technical help we give our customers, the more successful we will be.” 

“Well wasn’t that a condensation of what good business should be like?  He who helps his customer is the most successful,” she thought.

As she was thinking these thoughts a new email popped up on her PC. It was from Hal Lindsay, a noted curmudgeon.   Patty read on….

“ I heard you telling some of the people at the meeting last night that lead-free assembly had some process advantages: Hogwash. Lead-free has no process advantages, and it’s not needed,” he started.

After a few more complaints, he finished, “ It’s because of young tree huggers like you that never stood up and fought lead-free that we are in this mess to begin with.”

In preparing her response, Patty’s mind went back to some conversations about this she had had with The Professor. He had made two strong points:

1.       The first purpose of RoHS is to make recycling safer. So much recycling isperformed in poorer countries with chemically unsafe processes. RoHS compliant products will save the lives of the unfortunate people who have to perform this type of recycling to survive. 

2.       Lead-free soldering is challenging because the solder does not wet as well. This situation forced us to develop assembly processes with tighter process windows. However, an initially unseen benefit is that tighter lead spacings are possible with lead-free soldering because of this poore wetting. Many portable products such as mobile phones, could not be assembled with leaded solder. There would be too many shorts.

Patty was including this information in her response to grumpy Mr. Lindsay, when the phone rang. It was Rob.

He began, "我可能要出差去中国探访几家ACME在那里的新工厂。我想你可能也要在焊接工艺上做一些工作。"

(For our few readers that can’t read Mandarin: "It looks like I will be traveling to China to visit some of ACME's new factories there.   I think you will be going to work on some soldering issues too.")

“Whoa!,” Patty exclaimed, “Why would you be going to visit ACME’s factories in China?”

Rob went on, “You know things haven’t been going well here at AJAX, we never adopted “Lean Sigma” techniques like ACME did. Today, we had a layoff and I got hit.”

“Yikes!” screamed Patty. Her mind went through many scenarios with Rob being unemployed 5 weeks before their wedding.

“Easy girl,” Rob implored. “My GM called me in and said that he was sorry to see me go, but being a friend with your GM, he got me a job at ACME.   I am to be the liaison for the 3 factories that ACME has in China. My fleuncy in Mandarin made the difference,” he finished.

Patty and Rob were unusual for Americans, in that they both spoke Spanish and Mandarin. Both of their dads had encouraged them to take Mandarin at Tech as they had both taken many years of Spanish in high school. Both did a language study abroad (LSA) term and an internship in China. As their dads said, “If you can speak English, Spanish, and Mandarin, you can speak to almost any professional in the world.” Both Patty and Rob found that their language skills gave them a ready bond when they were abroad. One German colleague even told Patty that she was the only American he knew that would not fit the European view of Americans when they ask, “Are you bilingual, trilingual, or American?”

After Patty calmed down, she asked Rob why he thought she would be going.

He responded, “When your GM gave me the job offer on the phone, he alluded to a team visit to China, by me and this genius young woman that is a process expert. Apparently, they have some Head-in-Pillow, graping and productivity issues. I will be handling the business aspects, you the technical. He also mentioned he would like The Professor to go. I don’t think he knows we are engaged.”

Patty congratulated Rob and finished to conversation. She hoped that their being married wouldn’t create any issues in working together. She also was a little annoyed that she always seemed to be the last to know about trips that the executives were planning for her and her team. It was especially annoying that Pete seemed always know before her when they would need to go on one of their adventures. After all she was Pete’s boss. Well at least this time it was Rob, not Pete. There is now way Pete could know about this potential adventure.

She went back to finishing her note to cranky Hal Lindsay when she heard, “Pack your bags kiddo, it looks like China this time. Oh and Rob is going.”

 

Cheers,

Dr. Ron

I saw Patty at a recent SMTA meeting.  I mentioned that many of her fans would like to see a photo of her.  Surprisingly, neither of us had a camera.  As you remember she is also a self taught artist,  I asked if she would mind sketching herself.   Here tis.

 The reflow image of leaded and lead-free solder coutesy of Motorola.

Have you been watching the Olympics?  I knew I had been watching maybe TOO much of the Olympics when I heard that the medals were made from recycled, melted down circuit boards. 

No concerns here about head-in-pillow, solder joint reliability, halogens and all the other topics that make up the work lives of PCB assemblers.

More trivia: each medal is laser etched for that personal touch.  Not quite the same as the goal of making the original circuit boards which is to make thousands, if not millions, each one exactly the same as the one before. However, it is a great reward for the world class athletes' years and years of training and for surviving the Olympic experience.