INDIUM CORPORATION

After the report by Isofoton regarding reliability testing of Bi-based alloys for tabbing ribbon, the world learned that Bi-based alloys could survive the lamination process and function in use. If you haven’t seen it yet, I consider this mandatory reading! Here is the info: B. Lalaguna, P.Sanchez-Friera, I.J. Bennett, L.J. Caballero, J. Alonso, “Evaluation of Bismuth-Based Solder Alloys for Low-Stress Interconnection of Industrial Crystalline Silicon PV Cells", 22^nd EU PVSEC, Milan, 2007Milan, 2007.

We all know the Bi based alloys like 57Bi/42Sn/1Ag and 58Bi/42Sn can be used in a standard module assembly process, but is there an advantage to using Bi/Sn or Bi/Sn/Ag when Sn/Pb and Sn/Pb/Ag alloys are so well known and trusted in the industry?

I’ll give you 3 benefits:

1)    1) Bi/Sn/Ag and Bi/Sn are Pb-Free

2)    2) Bi/Sn/Ag and Bi/Sn are low-temperature alloys, they allow you to lower your tabbing process temperatures

3)    3) When paired with the correct flux and metallization, these Bi alloys form a powerful bond without microcracks (due to the lower process temperature)

Below are results with SunTab^TM ribbon assembled on a Komax X series stringer and tested on a XYZTEC Condor 150-3 bond tester (provided by the respective companies).

You’ll probably notice the lack of y-axis scale – I’m not going to give away all the cool information that easily! Contact me at jhisert@indium.com to learn more.

Here is a question that was posted and answered on our website back in 2006, I think it is still quite relevant:

Question: “Why does your Application Note for cleaning of indium ribbon for thermal interface recommend a mild (5-10%) HCl acid solution, yet [the] MSDS for Indalloy #4 (100%) says to avoid contact with acid? My past indirect experience with indium usage indicated some cleaning procedure of the oxides was necessary to achieve good thermal contact resistance.”

Answer: “Thanks for contacting the Indium Corporation with your request. If the indium ribbon is stored and handled (stored unopened in an argon or nitrogen pack – placed in a dry box) properly and it solders well in your process, this procedure should not be necessary. When following this procedure, the HCl solution should be applied to the indium metal to clean it thoroughly, and then dried with nitrogen.”

If you want to know more about metal thermal interface materials (TIMs) (handling, preparation, or process parameters), send an email to our global technical team at: askus@indium.com. They are ready to answer your question!

~Jim

Folks,

Let’s see how Patty is doing with the latest crisis……

Upon hearing Claire Perkins inform her that Rob was in the hospital, Patty froze and her face looked ashen. She quickly recovered and got her cell phone out to call Rob’s mother.

“Mom, what has happened to Rob?” Patty said, her voice quavering a little.

“He hurt his back at the gym, he can hardly walk. He collapsed under a heavy barbell. His head was injured too. He was unconscious for five minutes. I’m almost at the hospital now,” Rob’s mother, Hilde Gunther replied.

“I’ll see you there,” Patty said.

Both Sam and Mike insisted that someone take her to the hospital, but Patty refused. 

Patty looked at her watch, it was 9AM. Rob was working a “swing shift” for six weeks and didn’t have to go into work until 10AM, so he went to the gym from 7:30 to 9AM most days. Patty had been teasing Rob that his workouts were getting too vigorous. She knew he was trying to snatch over 250 pounds as he was in a friendly competition with one of his friends, Fred, to see who would be the first to accomplish this significant feat. She wondered if this goal led to his accident.

The drive seemed to take forever, but soon she was at his emergency room bed. Rob was awake but his face was black and blue.  Patty didn’t notice her mother-in-law, as she quickly ran to Rob's side.

“Rob, what happened?” Patty cried.

“The good news is, I snatched 250!” he chuckled, which caused him to grimace in pain. “It was 260 pounds that was my downfall, I collapsed under the weight,” Rob went on.

“How bad are your injures?” Patty asked, a little frustrated with Rob’s levity.

“My back hurts so much, I can hardly walk, my face just looks bad. I’m going for an MRI in a few minutes, they’re worried I might have a slipped disk,” Rob answered, becoming much more serious.

Just then an MRI tech came.

“Well Mr. Gunther, we are going to squeeze you in, so I need to put you ‘On Deck’ for an MRI that opens up. Realistically, it could be two or three hours,” the tech commented.

Both Patty and his mother kissed Rob on the part of his head that wasn’t black and blue as he left. After Rob was taken away, Patty chatted with her mother-in-law for about 30 minutes.

Even though to some people it would seem strange, Patty had a way of compartmentalizing things, she knew she could not help Rob, except to pray for him which she had already done. So, she decided to do some work on her laptop. Fortunately the hospital had WiFi.

Patty had some unfinished business from what she learned on her trip investigating NMAC/I/O. She wrote an email to the GMs of the sites that were using that cheaper solder paste that had the response to pause problems or that required kneading before being used, suggesting that they change to one of two corporate approved pastes that didn’t have these issues. She also wrote a note to the people that were using a full wavesoldering process for a PWB that had only two through-hole components, solder preforms should be used with the reflow process for a PWB like this she told them.

As Patty finished the emails she needed to send, she observed the activities of the MRI section of the hospital where she was waiting for Rob. It occurred to her that this was a process just like assembling electronics. Instead of stencil printers and component placement machines, there was an MRI machine. There were techs that ran the MRI machines just like there were operators. The nurses were like the process engineers, and there were some medical doctors that were like the mangers and execs at her company. Instead of producing electronics, the MRI section was producing MRI scans. There was really little difference.

Patty got curious and she decided to ask the scheduling assistant a few questions.

“Excuse me, my husband is getting an MRI and I have a few questions,” she asked Sara Carter the assistant.

“Sure,” Sarah said, “go ahead.”

“About how much does an MRI scan cost?” Patty asked.

“It varies depending on the extent of the scans needed, but $3,000 is a good estimate,” Sarah responded.

Patty asked more questions and learned that there were 5 MRI units and she assessed the headcount and floorspace needed to support the MRI unit. She also found out that each of the 5 MRI units averaged 9 scans per day. It then occurred to her that she could use ProfitPro to estimate the cost of a typical MRI scan. Under The Professor’s tutelage she has gotten quite good at estimating burden labor rates, etc, which would be needed for the calculation. She got her laptop out and using ProftiPro, in a few minutes estimated that the hospital’s cost of an MRI scan should be only $390!

“Why does it cost our insurance $3,000?” she thought.

It then occurred to her that her good friend from her days at Tech, Emily Chen, was a radiology resident at the hospital. She decided to send her a note and, in addition to telling her about Rob, ask about the MRI scan cost. 

After sending the email, she asked her mother-in-law if she would like to get a cup of coffee. In a short time, they were heading to the hospital cafeteria. Before they left, they found out that Rob was just starting his 45 minute MRI scan. 

Fifteen minutes later they returned, and Patty was surprised that she had already received an answer from Emily.

“Patty, I’m so sorry to hear about Rob. You probably won’t hear the official news on his MRI until tomorrow, but I will take a look at it and call you later today. BTW, my boyfriend works in the finance department here. I’ll find out about the cost. But, your numbers sound way off.”

Twenty minutes later Rob was finished. His doctor had given him some pain killers and muscle relaxers, so Rob was a little more comfortable, but the doctor wanted Rob to stay overnight for observation. Rob soon fell asleep from the medication. Patty decided to stay with Rob and by 4PM, she asked her mother-in-law if she could pick the boys up from day care.

At 4:30 PM another email arrived from Emily.

“Patty, good news. I looked at Rob’s MRI scan and it looks fine. He probably just severely strained a muscle. He’ll be as good as new in a month or so” Emily’s note began. Emily’s note went on, ”My boyfriend looked up the cost for the hospital to run an MRI scan. You were close, it costs $410. Neither of us can believe it. Where does the extra $2600 go?”

Dr. Ron note: I have done some investigations into MRI scan costs. As surprising as it sounds, these numbers are about right, the base cost for a hospital to perform an MRI scan is in the $400 range, but they have to charge $3,000 to break even. Considering that many hospitals are non profits and are losing money adds to the confusion.  At this point, I don’t claim to understand the cost structure of running a hospital, but one would think that one of the most critical questions in the current healthcare cost crisis in the United States, would be to understand why $3,000 must be charged for a $400 procedure to break even.  

The image is of Yegeny Chigishyov snatching about 450 pounds in the 2008 Olympics.

Two categories of solder are available to choose from when the in-service environment for a device reaches above 125°C either in continuous operation or thermal cycling accelerated life testing. These categories are those comprised primarily of lead, and those of gold. From the electronics industry’s drive to eliminate lead, many manufacturers who have traditionally used lead solders are treading cautiously, looking now at the gold solders, primarily at Indalloy 182 (80Au20Sn).

The most common concern regarding this switch relates to the strength of AuSn, which is much higher than the lead solders. The degree that this should be of concern however, should be realized within the scope of the application.

For instance, review this case scenario:

Indalloy 159 (90Pb10Sn) was used in a device for years to adhere high temperature sensors to a calibration probe that is slowly cycled in operation from 350K (~75°C) to 500K (~225°C). The solder joins a nickel and gold plated Kovar™, or platinum or platinum coated, nickel lead to a tinned copper lead. The solder joint is not placed under tension or shocked.

Considering the high temperature solder options in this scenario, the AuSn would be mechanically preferred.

Why?

Well, tin-bearing soft solders will leach gold from gold metallizations during soldering, creating a brittle Au-Sn intermetallic layer within the solder joint. The more gold available, the more consumed, and the greater the thickness of the resultant intermetallic layer. The brittle nature of this layer, situated intimately next to the relatively soft PbSn solder layer, creates differential stresses that promote crack propagation upon thermal cycling.

AuSn was not considered previously because the engineers were familiar with its hardness and, given the cracking failure described using a softer solder, they did not anticipate improvement. It was a pleasant surprise to them to find that switching to a lead-free solder would not sacrifice the quality of their device. AuSn is a brittle alloy but, unlike the description above, no differential stresses are involved. 

Note: Eutectic gold solders have been used for many years to solder nickel plated Kovar™ lids to high reliability ceramic packages and have a good history of fatigue performance.

I just attended the 2012 International CES in Las Vegas last week.  While the show was overwhelming and exhausting, the comprehension and implementation of these technologies and products was even more so!

A total of five Indium Corporation executives attended the event, along with 150,000 other people. We witnessed many new products, services, and concepts that ranged widely, from furniture, to kitchen electronics, to microprocessors, to monitors, to iPad covers.

When we regrouped to review what we had all learned, there were five different stories, experiences, and opinions. Each was valuable, as well as wildly incomplete and non comprehensive, and filtered through a unique lens - reflecting the person's personal background and perspective. After we all testified to our experiences, integrated each other's observations and conclusions, and synthesized the whole thing into one big story, were we able to get a good handle on what had occurred.

To me, what it all boiled down to is that:

1. unlike in "the old days" none of us will ever be an "expert" in any one field. I define "expert" to mean a person who is THE resource for info on a topic. These days, no matter how much a person knows about anything, another person can simply turn to the internet and gain much more information on any topic.
2. so many things are changing on so many fronts that, in order to maintain a respectable level of awareness and competence, a person can NEVER stop learning at a furious pace. Even WITH such an investment, a person can never become an "expert".

This felt quite a bit like the last several years in B2B Marcom. There is so much to become aware of, to experiment with and understand. To integrate. To measure. To evaluate. To change.

As B2B marketers, we need to become ultramarathoners – capable of a long, grueling, seemingly never-ending, experience. And we must be SMART! Our journey is doomed if we aren’t always learning, growing, well informed, making excellent decisions, and aren’t capable of making critical decisions on the fly.

Most importantly, no one person is capable of knowing it all, being able to take it all in, and become "the expert".  These days, it takes a team - it is the era of "we".  We need to learn together, we need to observe and experience things, we need to make decisions, and we need to review the feedback so that we make the best decisions.

CONCLUSION: Hand-select an incredibly bright and capable team, keep everyone in constant learning mode, and always work as one unit. If you don't, then expect another B2B Marcom team to beat you.

Folks,

Patty arrived at work an hour early to prepare for her meeting with ACME CEO Mike Madigan. Nineteen days ago, he had asked her to develop an electronics assembly metric that would correlate with profitability. This metric would, in turn, be able to help pinpoint opportunities for improvement. He gave her 3 weeks, so she was two days early. Mike was in town to meet with Sam Watkins, the local plant manager, so he ordered that they meet. 

Patty had quickly identified non-material assembly cost per I/O (NMAC/I/O) as a good metric candidate. She went to five of ACME’s plants and, after a day or two at each one, she collected all of the data she needed to prove her point. Rob helped her by writing an Excel® macro that would calculate NMAC/I/O and plot it versus profitability. The correlation coefficient was an outstanding 0.983.

While visiting the five factories, she tried to learn why those that had a poor NMAC/I/O were performing poorly. After a little checking, she and Pete discovered that the poor performing sites typically had lines that were not time balanced, had slow component placement machines, and occasionally had very slow printers or solder paste with poor response to pause. There was even one plant that was using a full wave solder process, when only 8 solder preforms would have done the job in the reflow process. None of these “problems” would show up if you were only tracking line uptime. In light of this situation, she also developed a plan to use NMAC/I/O to identify and implement opportunities for improvement.

As Patty headed toward Sam’s office, Sam’s administrative assistant invited Patty into the conference room to allow Patty to get her laptop set up. Just as she finished setting up and her Powerpoint® presentation was on the screen, Sam and Mike walked in.

“Coleman, we’re counting on you to take us to the next level,” Mike said a little gruffly, so let’s get this show going.”

Patty looked at Sam and could tell that Sam was uncomfortable with his boss’s abrupt demeanor.

“I performed quite a bit of research and concluded that non material assembly cost per I/O is the best metric,” Patty started.

“That’s great Coleman, but what the hell is non material whatever you said,” Madigan interrupted.

Patty’s cell phone vibrated, but she ignored it.

“Non material assembly cost per I/O is the total cost of running a factory less the components, hardware, and PWBs used. Some people call this the conversion cost,” Patty answered.

“If you think about it, it is almost obvious that this is the best metric,” Patty went on, “it measures all of the non material cost divided by how much we produce.”

“I get it,” said Sam, “we are producing I/Os or solder joints, we measure the total cost to make solder joints and divide by the number of solder joints. It’s that simple.”

“Precisely,” Patty responded.

“I understand now, why uptime alone wasn’t a complete metric. You can be up and running, but be doing it inefficiently,” Mike said with a rare smile on his face.

Patty’s cell phone vibrated again.

“Exactly,” Patty commented.

“OK, so we are going to measure NMAC/I/O,” Mike commanded, “How does it correlate to profit?” He finished.

“It is nearly perfect,” Patty said.

They continued their discussions and reviewed Patty’s plan to improve productivity at the sites with a high NMAC/I/O. Patty would take the lead on this effort.

As Patty got up to leave, Mike commanded, “Oh, and Coleman, find out why so few people use NMAC/I/O.”

Patty thought this was something to discuss with the Professor.

As Patty walked out of Sam’s office, Clare Perkins, Sam’s Admin stopped her.

“Ms. Coleman, your mother-in-law called, Rob has been taken to the hospital,” Clare said.

Cheers,
Dr. Ron

Yes, here in the central New York (CNY) region, a lot of state-funded activity is beginning to bud, even in the middle of a New York winter. Local academics have been busy. Professor Wolf Yeigh, President of State University of New York Institute of Technology at Utica/Rome (SUNY-IT) recently commented on his team's plans for academic excellence in nanotechnology and semiconductors:

"The projected Computer Chip Commercialization Center (Quad-C) and Center for Advanced Technology (CAT) complex will be on the main campus of SUNYIT. Construction will begin this year, and we envision that the complex will be 120,000 ft² of lab and office spaces complemented by up to 30,000 ft2 of clean room for Quad-C. The academic CAT building will be around 65,000 ft2 of academic and research space. The two buildings will be connected by a rotunda collaboratorium, and the entire complex layout will be similar to what you'd see at the Center for Nanoscale Science and Engineering (CNSE) in Albany, allowing a free flow of academic and industry R&D interaction along with the standard teaching and learning spaces.

Rather than duplicating fundamental research done at CNSE, our facility will emphasize further application and integration of nanotechnology research and development, including testing and evaluation. The academic departments at SUNYIT, working in conjunction with CNSE faculty, will offer courses and programs in nanotechnology applied to semiconductors, materials, informatics, biology and engineering (electrical, computer, civil, mechanical, bio, and materials).

Our major connectivity within the NY school system will be with CNSE. We will also work with community colleges and private institutions in the regions just as CNSE works with community colleges and institutions in the Capital Region and beyond."

The not-for-profit Mohawk Valley (MV) Edge group has been actively promoting the area as suitable for development, with control over 400 acres of land leased from NY State adjacent to the SUNY-IT facility in Marcy. Despite the fact that several years ago, the MV Edge failed in its bid to have AMD (now Global Foundries) locate their fab in Marcy, the region still stands ready to host a manufacturing facility. Already appropriately zoned and wetland permit-approved, with all new infrastructure ideal for a semiconductor fab or similar high-technology facility, the area may be ideally suited - if not for a fab - certainly for BEOL / 2.5D and 3D assembly processes, as the site is an easy drive (less than 2 hours) from the Global Foundries Saratoga Springs, and the adjacent SUNY-run CNSE facility in Albany, the New York state capital.

Local semiconductor, solar and LED-focused companies like Indium Corporation, and the first tenants in the proposed Quad-C building, Valutek and nfrastructure, will derive benefits from the close proximity of the SUNYIT facilities.

Nestled in the foothills of the Adirondack mountains (which remains the largest park in the United States), it looks like a brand new chapter may be about to be written, as the small Mohawk Valley region transforms from its old electronics moniker "RF Valley" to "Nano Valley".

Cheers!  Andy

Folks,

I thought I would post a few short thoughts as the new year begins. Here it goes:

1.    A billion hours ago the stone-age was the future, a billion minutes ago Caesar ruled Rome, a billion seconds ago Jimmy Carter was President, a billion passives ago you took your last break (about 4 hours ago). As exciting as the latest quad core microprocessor is, the largest number of components that we assemble is passives, approaching two trillion per year. That is about 6 billion a day. If you lined up all of the 7 billion people in the world, each year you could give every man, woman and child several hundred passives from all of the passives that are produced. If two trillion passives (assume 0402s) were lined up end to end they would circle the earth 50 times!

2.    Schools in Indiana are no longer required to teach cursive writing. Key board skills are considered more important.  Yikes! I’m all for keyboard skills, but I want my grandkids to be able to write in cursive. If not, how do they write their names? Are we less than a generation away from people writing their names as an “X?”

3.    Thoughts on lead-free solder reliability in long term mission critical environments from a NASA study:

        “Test vehicles assembled with lead-free materials (notably tin-silver-copper) exhibited lower reliability under some test conditions.”

Some people would respond to this statement by saying, “I told you that lead-free solder was no good.” However, another way of stating the results would be, “Lead-free solder performed better in more tests than tin-lead solder did.” The ratio, by my count, was about 5 to 3 in favor of lead-free. However, I agree that lead-free is not ready for mission critical (>20-year) service life. The main reason being that, in some cases, when lead-free solder joints failed in these types of studies, the results were much, much worse than tin-lead solder joints. These failure modes need to be understood and addressed. In addition, tin whiskers and pad cratering are looming problems in these, mission critical, long service life quadrant D applications as discussed in the Navy's Manhattan Project (http://www.navyb2pcoe.org/pdf/LFEMP_book.pdf).

4.    SACM has arrived. SACM is a SAC105 alloy that is doped with manganese. Work performed on SACM by Liu, Lee, et al was reported in a May 2009 ECTC paper, Achieving High Reliability Low Cost Lead-Free SAC Solder Joints Via Mn Or Ce Doping. The thorough testing reported in this paper suggests that SACM has promise as a material candidate for quadrant D applications mentioned in #3. In explaining the superior performance of this material the authors state:

“The mechanism for high drop performance and high thermal cycling reliability can be attributed to a stabilized microstructure, with uniform distribution of fine IMC particles, presumably through the inclusion of Mn or Ce in the IMC.”

We have had to wait awhile for this material to become commercially available as it is a challenge to manufacture doped solders like this in large quantities.  I think this paper should be on you "must read" list.

5.   I had not planned on reading Steve Job’s biography , as I thought I knew quite a bit about him from reading recent articles in Forbes, Fortune and Business Week. But I went ahead and downloaded it to my Kindle anyway. This work by Walter Isaacson is a masterpiece. To share one tidbit from it that relates to those of us in electronic assembly: 

"In almost all cases electrical engineers first design the circuits that perform the functions of some device like a mobile phone or tablet. Mechanical Engineers are then left to fit the circuits into the “box.” (Hence MEs are often called “box stuffers” by EEs). Jobs completely changed this approach. He told the engineering team how he wanted the product to look and function first, then they had to determine how to make it work that way. I’m convinced that only through this approach are the revolutionary design concepts that Jobs and Apple came up with possible."

The book also points out his many flaws (e.g. Jobs would regularly park in handicap spots, the author reports several times that Jobs just didn’t think the rules applied to him, etc.). Another interesting thought (read it and see if you agree with me) that if Steve was not Paul Jobs' adopted son, Apple would have never happened.

Cheers,

Dr. Ron

平时在向客户们介绍Indium 8.9系列的免洗焊锡膏时，除了问客户们一些具体的需求时，最重要的问题之一，就是“你们需要做ICT测试吗？(In Circuit Test)”。 一般的测试有两种，一种是Functional Test, 就是接通上电源，看看板子工作不。再具体的一种就是In Circuit Test （在线测试）。

免洗锡膏都会有残留物(paste residue)留在板子上，有时候探针不太容易刺入残留物进行ICT，所以Indium 8.9系列焊锡膏中有专门为便于ICT测试而研发的锡膏，比如说Indium 8.9， Indium 8.9HF1。 在锡膏的成分里面，有Softener（软化剂）。之所以Indium 8.9， Indium 8.9HF1 的残留物比较软，就是因为软化剂含量相对较多。

当然，这不意味着不是专门为ICT而设计的锡膏就不使用与ICT。一般的锡膏残留物是Rosin/Resion（松脂），软化剂含量相对较少，但是松脂不是石头，只要探针有合适的测试设置（如力度），还是可以进行测试并读取准确的数据的。我们就有一个大客户，以前一直在用我们的一款不是专门为ICT测试而研发的锡膏。后来这个客户引入了ICT测试，但是又不想换锡膏，我们和ICT Probe的供应商一起帮这个客户调试了一下ICT的设置，也使ICT能偶顺利进行。

Happy New Year!

Pic: Google Image

一直有些客户在问我们这个问题：你们有没有免洗锡膏也可以被清洗干净的？

水洗锡膏（water wash paste/water soluble paste）和免洗锡膏的最大差别，在于锡膏中是否含有Resin/Rosin（松脂）一类的物质。 在水洗锡膏的助焊剂中，因为活性剂(activators)最后都是要被清洗干净的，不然会腐蚀板子，所以没有含有松脂。也正是因为没有松脂的保护，水洗锡膏中助焊剂的热稳定性（thermal stability）没那么好，所以水洗锡膏一般不适用于较长和较热的炉温曲线（reflow profile）。

在免洗锡膏中（No-Clean paste）,有松脂(Resion or Rosin)。所以锡膏回流后在板子上的残留物能够很好地被“密封”起来，不会造成板子的腐蚀或是导致电路板短路。 我的同事Eric Bastow很喜欢用这个故事向客户们栩栩如生的解释松脂强劲的密封作用： 大家都看过《侏罗纪公园Jurassic Park》这部电影吧？里面恐龙的基因你们还记得是怎么被人们找到吗？是在一个蚊子里面。几千年前的蚊子被琥珀密封好了，无论外界环境如何恶劣，日晒雨淋，极寒或是极热，到了今天，蚊子里面的基因还是可以被提取出来。琥珀的成分主要是松脂，所以我们可以以此得知松脂的强劲密封能力了。

曾经有一个大的加工制造厂，为一个大的OEM客户做清洗免洗锡膏的实验：清洗10%， 30%， 50%等，看看残留物的可靠性(SIR & ECM test)。 结果是可靠性最高的还是完全不洗，或是完全清洗干净。

所以Indium公司的建议是要么完全不清洗，用免洗锡膏；要么完全清洗干净，用水洗锡膏。

Cheers!

Pic: Indium Corporation

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

Recently I was testing the resistance of a new low temperature metallization paste* (for solar photovoltaic assembly) in the lab. The samples were initially tested with a 4-point probe, just before entering a chamber set at 85°C and 85% relative humidity. To my surprise, the resistance dropped noticeably (as seen in the chart).

I brought the results to the material’s creator in our R&D department, ready to wow him with my discovery. I exclaimed, “I just finished testing the samples we put into the 85/85 chamber and can’t believe the values I’m getting!” Without a flinch he replied: “The resistance went down, didn’t it? That’s a unique feature of this material.”

While I didn’t gain any cool points in R&D for discovering an awesome new feature of an upcoming product, I hope the trait of this material can be useful for our customers (some of whom have since noted the improved characteristics after reliability testing).

The thing I learned from this experience is how important end of life testing is for metallization paste – all too often samples are only compared based on time-zero testing. This will change the way I compare metallization pastes from now on.

~Jim

*For my followers who aren't familiar with low-temperature metallization paste,it is also referred to as "grid ink", "silver ink", and "conductive ink". Low-temperature metallization paste is a silver-filled contact material used in the assembly of photovoltaic solar cells. It gets its low-temperature label because it is processed at lower-than-traditional glass frit temperatures of ~1,000°C. In addition to its role as a contact for thin-film connections, low-temperature metallization paste is also useful as a low-temperature alternative metallization on Si-based cells.

Learn more here.

Indium metal has the unique ability to cold weld (bond) to itself at room temperature. Though this is, technically, not soldering, this property makes it especially useful for low-temperature bonding applications. Back in 2008 I mentioned indium cold welding on the semiconductor packaging blog. Here are some other resources for learning more about the process:

• The official Cold Welding Application Note
• Using indium in a cryogenic seal application.
• Using indium in Flip-chip applications

Cold welding is a great solution to some really tricky bonding applications. Some nice features of using indium cold welding as a bonding method are:

1) It offers an instant attachment. Because indium will stick together upon physical contact (with a slight amount of pressure) the bonding process takes a fraction of a second as opposed to reflow soldering processes for solders or curing processes for epoxies – which can take seconds to many minutes.

2) It requires no heat. Temperature-sensitive components can be assembled without heating. The stresses that occur due to CTE (coefficient of thermal expansion) are also not an issue, which makes this a great process for attaching large dissimilar CTE materials like brittle ceramics and high expansion rate metals.

3) The bond will have exceptional thermal and electrical conductivity due to the nature of the indium that is used for this process.

You can use the indium cold welding process on any material you can successfully sputter, evaporate, reflow, or plate indium onto.

The answer to the age-old question: “What is the expected lifetime and associated strengths of an indium cold weld?” is:

The cold weld bond will last indefinitely and the bond strengths approach that of a solid piece of indium, 273 PSI.

If you have questions, please email them to askus@indium.com.