Flux

在表面貼裝技術(SMT, Surface Mount Technology)以前，主要流行的是波峰焊(Wave Soldering).   雖然現在大部分的電子產品焊接都是SMT，但是某些不需要微型化(miniaturization)的產品，如DVD播放機，還有波峰焊的低成本優勢，都是波峰焊技術至今還存在的主要原因。 Indium公司的資深顧問Dr. Ron Lasky曾經説道，波峰焊技術在我們的下一代，下下一代，都應該還存在的。

最近又有一個客戶和我們一起探討波峰焊助焊劑(wave flux)的殘留問題。他們使用的是免洗(no clean)助焊劑。正是因爲免洗，所以各種不同的助焊劑，有不同量的殘留。 而客戶的客戶，也在對殘留的多少有一定的疑問。 其實現在在IPC的規定中，沒有具體規定免洗波峰焊殘留的多少是符合要求的。 最後我們根據客戶對焊接外觀和可靠性的綜合要求，推薦了最適合的一款產品。

Cheers!

PS: 一些年長的客戶或是合作夥伴總是開玩笑說“我在這個行業工作的時間一定比你的年齡長。想當年手工焊接或是波峰焊的時候……”

Pic: http://enc.ic.polyu.edu.hk/Zhengde/z2003/ws/images/pic2.png

I’m really excited about a new option for those of us who are prototyping solar assemblies or evaluating new tabbing ribbon materials. I’ve been waiting for something like this – everything you need to solder solar cells together in one package. The turn around time is key too – you may recall an older post where I learned how quickly these materials shipped.

On the website where these kits are offered, the description reads:

“Tabbing ribbon kits come with everything you need to evaluate how Indium Corporation materials will work with your solar cells and assembly process. The kits can be used to:
- Evaluate which tabbing ribbon size is best for your design
- Determine which flux is best for your operation
- Experiment with new solder coating alloys
- Assemble a few solar panels”

The tabbing ribbon kits come in 3 flavors:

- Standard Sn/Pb/Ag (62Sn/36Pb/2Ag)

- Pb-Free (96Sn/4Ag)

- Low Temp Pb-Free (58Bi/42Sn)

I have a feeling the Low Temp Pb-Free kits are really going to be the most popular of the 3 that are offered though. Application temperature ranges will determine which kit to use, but all three versions of the kits are said to offer similar base copper sizes and tolerances:
“The ribbon itself is industry standard CDA 110 (99.9% Cu) core flat wire, coated with a precisely controlled layer of solder. Each ribbon is manufactured using our proprietary softening process so you can increase the yield of your stringing process.” Basically, this means that the softer tabbing ribbon will help eliminate the breakage of thinned cells during the heating/cooling cycle.

It also includes some matching bus ribbon to complete your panel build. If you’re trying to find the right flux, this kit serves dually as a flux evaluation kit as well. The kit is loaded with VOC-Free flux, rosin-based flux, and resin-based tabbing fluxes. I prefer GS-5454 as a flux for most tabbing operations, but you can see how the others stack up as well.

Let me know how you like the kit after you try it out!

~Jim

(jhisert@indium.com)

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

Folks,

After a bit of a break, the adventures of Patty, Rob, and The Professor continue:

The plane droned on as it made its slow march from Detroit to Tokyo.   Patty looked down at Rob as he slumbered peacefully. She caught a glimpse of The Professor,  he looked at both of them from across the aisle with a satisfied smile. The proud mentor looking at his mentees. 

This was the first time in a while when Patty didn’t feel totally stressed. She had resisted going to China only three weeks before her wedding, but senior management insisted. She would arrive home only 5 days before the big day. She and Rob had their first real fight, she got angry with him because he wasn’t appreciating the pressure that she felt. However, with one long weekend with their moms, she was able to get most of the tasks done and finally felt relaxed that the wedding plans were in good shape.

She had to chuckle at Rob. He was all nervous being with The Professor by himself. The plans that they had made had Rob and The Professor focusing on productivity improvements at ACME’s new acquired plants in China. While they were working on these tasks, Patty would handle some process materials related issues. 

The rest on the trip went smoothly and after a night’s rest they were off to the first of ACME’s new factories. This one was located in Shenzhen. Our trio was ushered in to see the site GM, Peng Zhou, a native of the area. He addressed them in quite good English. When Rob and Patty answered in better Mandarin, he seemed shocked. When The Professor answered him in flawless Cantonese he and Patty and Rob were stunned. 

"要不咱们都讲中文吧，既然咱们中文都不错。" said Rob. ("Perhaps we should all speak in Mandarin, since we speak it well." For our non Mandarin speakers)

Rob and The Professor went off to audit a few assembly lines, while Peng accompanied Patty to visit an assembly line that was having a quality problem.

(Dialogue translated from Mandarin)

“I’m very impressed with how well you all speak Mandarin,” said Peng. “Where did you learn it?” he continued.

“Thank you,” replied Patty. "Both Rob and I studied Mandarin in college and we did an internship in China,” she went on.

“ Very impressive,” Peng commented. “But I have to tell you, I’ve never heard any American speak Cantonese at all, let alone as well as The Professor does. It’s like he was born here,” he went on.

“He never ceases to amaze me,” Patty responded.

Patty and Peng finally arrived at the assembly line. Patty was introduced to the line engineer, Elvis Chang. She chuckled inside, this was the third Asian person her age she had met that had chosen “Elvis” as an English nickname. Elvis was relieved that Patty spoke Mandarin. They went to a stereo microscope and looked at some of the assembled PCBs that had quality issues. Patty was quick to pick out the problem:  graping. She looked at the stencil and the pad sizes on the PCB. She performed a few calculations and appeared satisfied that she had the answer. Patty suggested that, if Elvis would like, she could give a brief presentation on what she thought the problem was.

“Patty, that’s a great idea, but it might be best to wait until after lunch,” Elvis suggested.

Elvis, Patty, and a few other young engineers went together for lunch. They seemed to be fascinated with Patty, especially her ability to speak Mandarin. They all spoke some English and were all studying it as they recognized that their ability to be promoted to a senior level required fluency in English. One of them pointed out that she had read that about 250 million Chinese people are studying English, while only 20,000 Americans are studying Chinese.

Patty enjoyed Chinese food and was happy to find Sea Cucumber on the menu. One of her friends said it was the only Chinese food he couldn’t eat. She tried it and liked it.

After lunch, Patty asked for a few hours to prepare her presentation. Her main points are summarized below:

1.        The aperture size for the pads that experience graping is 8 mils in diameter for the 4 mil thick stencil.

2.       The resulting area ratio (D/4t, D= diameter, t = stencil thickness) for this aperture is 0.50, less than the recommended 0.66.

3.       The very small solder paste deposit doesn’t not have enough flux to avoid oxidation of the solder particles in reflow. The resulting defect looks like a bunch of grapes so it is called graping.

4.       Likely solutions:

a.       Use a square aperture. An 8 mil square aperture provides 27.3% more volume, and it has better transfer efficiency. (Transfer efficiency is the volume of the solder paste deposit divided by the volume of the aperture times 100.) The result would be > 30% more solder paste. The more solder paste, the less likely to experience graping

b.      The solder paste they were using was not best of breed re: graping resistance. She recommended another one, which she knew performed well in all respects - and minimized graping. This solder paste’s flux was robust and designed to minimize defects like graping.

Her presentation was received very well. Fortunately some of this excellent solder paste she recommended was being used for another job in the plant. So with approval from Peng, the team switched to this paste.

After the meeting, Patty thought about how much one of the technical engineers from one of her favorite solder paste suppliers had helped her to understand graping and how to minimize it. His name is Ed Briggs and she had just attended SMTA Toronto where Ed gave a paper on graping. Much of the information in her presentation came from Ed’s paper. She had also learned from one of his blog posts on graping.

Epilogue: Three weeks later, the graping had disappeared from Elvis’s assembly line. They didn’t even need to adopt a stencil with square apertures, the solder paste change, itself, was enough.

Cheers,

Dr. Ron

前段時間有一個客戶，詢問了我們如何解決解決錫膏粘刮刀問題。 產品是Indium公司有鉛產品的黃牌Indium 92J.

詳細了解了客戶的使用過程后，我們給出了以下4個建議：

1．   提高印刷速度print speed.  錫膏的flux設計中，有一種叫做Rheological Additives的材料。正是這種材料，能使錫膏在儲存的時候，金屬粉和flux能夠均勻融合在一起，不會出現分層現象。而在印刷時，印刷的剪切力使viscosity 下降，能很好的下錫。但是，如果印刷速度太慢，Rheological Additives不能使錫膏很好的滾動起來，就會出現錫膏粘刮刀問題。 所以，印刷速度因該在合理的範圍内。

2．    関掉EAU Environmental Air Control.  很多新買的印刷設備，使用時都會忘記關上EAU，就是“空調”。 太冷了容易使錫膏viscosity 增加，造成錫膏粘刮刀。

3．    檢查金屬成分比Metal Load.  每一款產品，都由最適合自己的金屬成分比。金屬成分比稍微偏高了，也會造成錫膏粘刮刀。  隨著無鉛化和微型化，無鉛的4號粉金屬成分會相對低一點。

4．     檢查錫膏在網板上面的放置。 一般來説，在網板上面不能放置太多的錫膏，使錫膏粘到刮刀的holder上面了。這樣當然會粘住刮刀，不利于印刷。

如果有任何技術問題，歡迎隨時訪問Indium的online support網站：http://knowledge.indium.com/  或者隨時發郵件給我們：askus@indium.com ,  china@indium.com

Cheers !

Pic : Indium Corporation

I mentioned in a previous a blog posting that the primary driver for halogen-free electronics is ostensibly environmental, but that the confusion about “which halogens and which molecules and what level?” has seemingly decoupled the laudable desire for an improved environment from the reality and made it more of a marketing tool. All this notwithstanding, there remain some instances where the performance of the final product itself can be directly impacted by the presence of halogens, usually as ionic halides. This is the reason why Indium Corporation recently developed what appears, at first glance, to be an odd combination: a high-Pb (high-lead) alloy halogen-free die-attach solder paste, Indium9.72-HF.

The halogen-related failure mode for die-attach solder pastes is the corrosion of wirebond pads on the topside of Power Semiconductor die which are soldered to the leadframe with halogen-containing solder paste. Many manufacturers producing high volumes of identical power devices may also use die-attach (sometimes called “soft solder die attach”, SSDA) wire to attach the die to the leadframes in a fluxless process, but many manufacturers prefer the inherent flexibility of a solder paste-based process for medium mix / medium volume applications.

Long term blog readers will recall that I did a posting on solderspatter (a.k.a. soldersplatter or soldersplash), and that it can be caused by bubbles of solvent vapor or moisture outgassing from solder paste deposits during reflow. In bursting, the tiny flux droplets or solder particles from the surface of the bubble can be propelled quite a distance (several feet). While solder on wirebond pads is clearly a failure from a reliability viewpoint, certain wirebond pad metallizations may also be subject to corrosion from flux. A poorly maintained reflow oven may also drip flux condensate (usually in the exit – cooling – zone), and this too can be a cause of organic materials on wirebond pads.

As long as the bondwire is gold, and wirebond pads are covered in a uniform layer of gold, there is no problem (as long as the flux residue is washed off) since gold is unreactive, even in corrosive environments. Aluminum (Al) or aluminum/silicon (Al/Si) bondpads, however, are potentially reactive. Halogenated materials, such as fluxes and overmolding compounds may react with them to either reduce the wirebond pull strength and/or increase the wirebond junction resistance, leading to localized heating and subsequent thermal-related joint failure. Even covalently-bonded (C-X, where X is a halogen) materials may dissociate at high temperatures: which is how the banned brominated flame retardants work, of course.

The biggest danger of halogenated flux corroding wirebond pads is when:

1/ Completed assemblies (between the reflow process and the cleaning process) are left for a long time before cleaning; particularly if they are exposed to high humidity (high %RH) before cleaning.

2/ The cleaning process is inadequate: either due to poor selection of the cleaning solution, or poor bath maintenance, or inadequate “scrubbing” energy being imparted to the surface to be cleaned, or simply if inadequate time is allowed for cleaning.

Note that even optimizing 1/ and 2/ may still lead to bondpad corrosion.

The Indium9.72-HF paste is available in both type 3 and 4 powder, in the standard high-Pb alloys, Indalloy 151 (92.5Pb/5Sn/2.5Ag) and Indalloy 163 (95.5/2Sn/2.5Ag), and for larger die that need a higher reliability joint, we also offer the Indalloy 164 (92.5Pb/5In/2.5Ag). A Product Datasheet is available for download, of course.

Cheers! Andy

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!

This blog has been in existence for a little over two years now, and we would like to thank our readers for the feedback and inquiries you have provided. I welcome your comments on what you would like from us. Leave a comment below, or email me at jhisert@indium.com.

And now a look back on past topics of interest:
 

Grid Ink, Silver Ink, Conductive Ink

Bismuth/Tin Tabbing Ribbon, A Low Temperature Pb-Free Alternative

Plated Metallization for C-Si Solar Cells

Increase Packing Density for Evaporation Crucibles

Photon’s 5th PV Tech Show 2010 USA

IPC Solar Standards Update

Solder Shelf Life as Explained by Eric Bastow

Tips to Speed Your Solder and Flux Selection

What's Happening in the Technical Service Department 

A Day in the Life of a Tech Guy

A Clean Laboratory

CIGS for Beginners

3rd Renewable Energy Expo 2009 in New Delhi, India

Solar Products and Representatives

Kleenex®, Google™, FedX®, CIGs?

Indium Solar Products Reunited

Trade Show Visitors Love the Ground Floor

Solar Product Data Sheets

Intersolar 2009 – What Barrier to CIGS Technology?

Concentrator Photovoltaic Systems - Will they reach 50% Efficiency?

Standards for Solar Panel Manufacturing

Solar Panel Certification: “Barrier and Benefit” Reviewed by Eric Bastow

Low Temperature Metallization Paste

What Will Your Interest Be At InterSolar? Meet the Bloggers And Let Us Know.

Share Your Solar Images

SAC vs. Sn/Ag for Solar Soldering

Solder Thickness for PV Interconnect

What is Bus Ribbon?

Standard PV Interconnect Ribbon Sizes

No-Clean Flux

Photovoltaics in EMS Sector

PV Interconnect Products

Eric Bastow - East Coast Technical Support

Mario Scalzo - West Coast Technical Support

Au/Sn Sputtering Targets

SMT Goes Solar

A Trip Down Memory Lane 

More Information About Metallization Paste

A year in the Life of a Solar Blog

CIG Target

23rd European Photovoltaic Solar Energy Conference and Exhibition

TCO choices for CIGS manufacturing 

CIGS Absorber Layer Electroplating

No Slump Metallization Paste

Meet the Bloggers

CIGS - Can sputtering make a breakthrough?

Fluxes for Soldering Tabbing Ribbon

Computer Brain vs. Solar Photovoltaic

Beam it down from space

Selection of the Optimum Lead-Free Solder for Solar Tabbing Ribbon

Record Makes Thin-Film Solar Cell Competitive with Silicon Efficiency

Why Thin-Film Solar Cells are Here to Stay

Hot Rooftops to Flashy Digital Cameras

Synchronize Your Solar Cell

Solar Conversion Efficiencies  

Government Support is the Key

It's Just a Beginning ...

Graping is a phenomenon which appears as un-reflowed solder particles, typically seen on the surface of the solder joint.  



             Cross-section of “graped” solder joint





The graping phenomena has become more common due to some of the following issues:

1. Reduction of the stencil aperture to accommodate smaller and smaller discrete and passive components (i.e. move from 0603”s to 0402”s to 0201’s)
2. The use of finer particle size solder pastes to accommodate fine feature printing (move from Type 3 to Type 4 to now to Type 5)
3. Higher reflow characteristics for Pb-free soldering
4. The use of water-soluble vs. no-clean solder pastes. No-clean chemistries generally protect the solder powder particles and the metallized surfaces from oxidation during the heating process (after the activator package removes existing oxides). (so how does water-soluble fit into this?)

A combination of any of these factors may exhaust the capability of the solder paste flux to remove surface oxides. This depletes the flux and exposes solder paste particles to oxidation, which means the solder particles do not coalesce into the solder joint.

To avoid the graping phenomenon, use the following tips in setting up your reflow profile. The intent here is to decrease the amount of heat the solder paste experiences during the reflow process.

1. A ramp to peak profile is better than a soak profile   
2. Decrease total time in oven by adjusting the belt speed. A ramp rate of 1°C/ second from ambient to peak is recommended
3. Use a lower peak temperature - 235°-240°C
4. Shorten the TAL to 40-60seconds

Okay, I have a confession to make: I’ve always had a grudge against bismuth, ever since I started recommending thermal interface materials. It is the polar opposite of my favorite element (indium) – well, as much as a metal can be. These 2 elements (indium or bismuth) are added to almost every solder with a lower solidus temperature than Sn/Pb. The choice for most thermal interface applications that I have dealt with was indium or an indium alloy, but now I am starting to become very fond of my new friend bismuth for solar applications.

Bi/Sn and Bi/Sn/Ag are now available as a solderable coating for our Tabbing and Bus Ribbon. After getting a feel for this material, I must say I find it pretty nice to work with. Both alloys melt at 138-139degC, with the Bi/Sn/Ag having a greater tensile strength (which is not necessarily a good thing for tabbing ribbon). With a little bit of lab time I have isolated an existing flux that works very well with these alloys. So far GS-5454 has formed good solder bonds down to 160degC. This is great news, because it allows you to minimize the reflow temperature (and stresses) of your C-Si/tabbing ribbon interface. 

~Jim

Reflow profiling can be broken down into several phases. I generally use the following;

Preheat

Pre-reflow

Reflow

Cooling

Preheat Phase preconditions the PCB assembly prior to actual reflow, removes flux volatiles, and reduces thermal shock to the PCB assembly. Because the preheat phase is often the longest of phases the ramp rate (rate/rise of time vs. temperature) is often established in this phase.

Pre-reflow Phase involves flux activation to remove surface oxides (on mating surfaces as well as the solder paste particles themselves), further pre-conditions the PCB assembly before reflow, and can be utilized for the soak portion of the profile, if needed. A soak profile may be suggested to diminish any delta T between components if there are both very small and very large components or the physical size of the PCB assembly is very large in and of itself. A soak profile is also often suggested to reduce voiding in area array type packages, though with Pb-free chemistries, this is often not as effective as with SnPb.

Reflow Phase is where the mechanical/electrical connection is made through the formation of intermetallics. Peak temperature and TAL (time above liquidus) help define the actual reflow portion of the profile. Peak temperature 20-40°C above liquidus and TAL of 30-90s is common.

Cooling Phase determines the grain structure when solidified and is defined as the solder cools from the peak temperature to solidus. A fast cooling rate is desired to create a fine grain structure (most mechanically sound) but is limited by the differences in CTE (coefficient of thermal expansion) of the joining surfaces. If excessive, stress can be exerted on the solder joint or component, fracturing or tearing can occur. Cooling rate of 4°C/s is commonly suggested.

Ramp to Peak profile depicted

For more please see “Best Practices Reflow Profiling For Pb-free SMT Assembly"

Patty, Pete, and John prepare to do battle with "The Big O."

Patty and Pete were able to squeeze in 9 holes of golf, though it was really stressful for Patty. Pete was a good golfer, but not in Patty’s league; he typically shot in the low 80s for 18 holes compared to Patty’s 68-72 range.   Today, going into the 9^th hole, Patty was even par and Pete was one under. He was teasing her relentlessly.   The ninth hole was 532 yards long. Patty used all of her recent training and focused as she drove the ball. Her swing speed hit 114 mph and with a 4 mile an hour tailwind, her drive was 291 yards, 30 yards beyond Pete. Her second shot, with a five wood was 12 feet from the pin. Her putt was dead center for an eagle, Pete’s 8 foot birdie putt lipped out of the hole. Whew! She beat Pete by one stroke! Pete was still thrilled that he gave Patty such a close call.

As they left the golf course, Pete said, “John is really working miracles at the factory, given the constraints he is working under. He has developed a disciplined approach to changeovers and uptime, and has eliminated most waste. But the factory really needs to be cleaner and more organized. With all that is on his plate, and no cleaning staff, he will have trouble implementing a 5S. It will be hard to win new customers with the place looking like it does.”

The next morning, as they prepared for the meeting with Oscar Patterson, Patty noticed that John’s color was ashen.

“John, are you alright?” Patty asked.

 “You’ve never been in a meeting with Mr. Patterson. He can be a bit…uh…. difficult,” John stumbled out.

“From what I hear he is a ruthless, brutal dictator,” Pete added.

John did not disagree.

Patty thought it might be best to call back to her site GM to clarify her mission.

The GM told her, “This guy is a blowhard, it would be great if you could review with him your findings and get his buy-in. But, don’t take any grief from him. He forgets that he sold us his company. Now he has a boss, and it is me. I told him you were going to perform an audit and I want him to work with you.”

So Patty, John, and Pete went to Oscar Patterson’s office to review their findings. Patty was immediately intimidated by him. He was a huge man with a ponderous stomach. But the posters in his office were the worst. One read “I’m the Boss, you aren’t.” Another read, “My way or the highway.” Then she saw, “The Golden Rule of Management: Whoever has the gold makes the rules.” The last one she took time to read was especially troubling: “It’s a question of mind over matter: I don’t mind and you don’t matter.”

Patterson spoke first, “Let’s get this over with, I don’t have time to waste on this nonsense. I’m the boss and I’m responsible for profits, so give me your crap and get out of here.”

The Professor always advised Patty that after an audit it is best to present the strengths first and then the problems. However, never call the problems “problems,” call them “opportunities for improvement.”  “I learned this from my colleague Joe Belmonte,” The Professor told her. She had since met Joe at a few trade shows and was impressed by his wealth of experience and in-depth knowledge of assembly processes.

She started by discussing the very good 25% uptime, and the fact that the operators were quite good at changeovers.  Pete had pointed out that the operators told him that John was responsible for both of these successes. The operators liked and respected John, but realized he had a tough job working for Patterson.

As imagined, Patterson warmed up to this compliments. 

“I told ACME management that buying my company was a good deal. We cut costs and I am able to make a profit even though I have losers like John working for me,” Patterson bragged.

Patty was furious at this comment. Pete looked like he was going to jump across the table and take a swipe at the “Big O.” John just sat there looking defeated.

“This isn’t as bad as I thought it would be,” boomed Patterson. “Continue.”

Patty then reviewed the 7 mudas. She had been surprised that the company did quite well in this part of the audit also, undoubtedly attributed to John:

1. Overproduction

2. Unnecessary transportation

3. Inventory

4. Motion

5. Defects

6. Over-Processing

7. Waiting

Hence, Patty’s comments were positive on this topic.

“You'se guys aren’t so bad,” boomed Patterson. “I told you I was good at generating profits, even stuck with a dufus like John here,” he finished.

At that comment, Pete’s faced turned the most crimson Patty had ever seen.

Patty then went on to “Opportunities for Improvement.” She thought she would start with 5S.

“We performed a “5S” audit of your facility. This manufacturing philosophy consists of:

1.       Sorting

2.       Set in Order

3.       Shining

4.       Standardizing

5.       Sustaining the Improvements,” she started.

“As ACME strives to get more customers for our contract manufacturing services, 5S is an important consideration, as many of our current and future customers practice Lean and especially 5S at their facilities,” Patty added.

As she went on she reviewed the lack of order and cleanliness in the facility. She had photos of dried solder paste on the stencil printers, the flux and dust “stalactites”, and several other examples of 5S violations. Patterson’s face soon matched Pete’s in its level of sanguinity. But he said nothing.

Patty then volunteered that she and Pete would work with John and his team to implement a 5S if desired.

Patty could see Patterson was ready to blow, but she felt she must go on. The only topic left was turning off the nitrogen in the wave soldering machine.  As Patty played the wave soldering video, surprisingly, Patterson seemed interested. 

She continued, “We think an opportunity for improvement would be to re-instate the use of nitrogen in the wave soldering process. First pass yields have dropped from 94% to 87%, thus increasing re-work. Or, perhaps, implementing a more robust wave solder flux. I contacted a wave flux vendor and I have some recommendations.”

At this Patterson became even redder in the face, in a rage he grabbed Patty’s laptop and threw it on the floor, instinctively Pete dove for the laptop, spun around and inserted his chest between it and the floor.  Patty had never seen such agility in a 45 year old man.

“You bozos are worse than John the clown here!" he shouted, as he gesticulated toward John. 

Patterson then kicked the trio out of his office. Pete was ready for a fight, but John and Patty, both visibly shaken, held him back.

Patty immediately called Sam, her GM, and told him in detail their findings and what happened at the meeting. She gave a good impression of what John had accomplished in spite of Oscar Patterson.

“Wow! Patty, I’m so sorry. I didn’t expect it would be this bad. I’ll change my schedule and fly there today. This situation will not stand. Why don’t you and Pete take a break and meet me for dinner at Dinardos at 7PM? Bring John with you.”

Patty was glad that she backed up her files last night on SugarSynch, even though it looked like her laptop was fine. 

Colonial Williamsburg was only a 45 minute drive away, and it was just 10AM. Taking Sam’s advice to “take a break,” she and Pete drove away and toured this beautiful living museum. They also had lunch at the Trellis.

Surprisingly, with the Williamsburg respite and all of the walking Pete and Patty did, they were more relaxed and hungry than they thought they would be. 

On the way back to Dinardo’s Patty asked Pete, “How did you save my laptop, I’ve never seen such an agile, athletic move?”

“Twenty-nine years of beach volleyball,” Pete answered.  “I was good enough that I tried out for the Olympics  in ’92. Humbling experience,” he added.

About 10 minutes before they arrived at the restuarant, Patty's mother called with updates on the wedding plans.....only 10 weeks and counting!

John had arrived early at the restaurant and Patty and Pete met him. He looked very nervous. 

“John, how’s it going?” asked Pete.

“It’s hard to be optimistic,” John answered.

On that note Sam walked into the restaurant.

“This must be John Davis, the new GM, having replaced Oscar Patterson,” Sam stated with great cheer.

These words didn’t seem to register with John.

“Congratulations John, well deserved,” Patty and Pete chimed in.

In the few days they were there, Patty and Pete had grown quite close to John.

As the information sank in, tears welled up in John’s eyes.

“Do you think I’m up to the job?” he asked.

“John, you are already doing the job,” Patty answered.

Epilogue:

Sam had felt it best to have the police accompany him to see Oscar Patterson with the news that he was fired. Patterson became so agitated that the police had to threaten to arrest him before he calmed down and was escorted out of the facility.

With John at the helm, the “shop” was not recognizable in 3 weeks, as he implemented a 5S program that he designed with Patty and Pete.

He performed some DOEs to find a wave solder flux that could perform well, without nitrogen, for most of his applications. However, he still used nitrogen for a few boards that had a large thermal mass. All of these, and the many other, decisions he made were data driven.

Have you performed a Lean audit of your facility? Do you regularly practice 5S and look to eliminate the 7 mudas? Are your decisions “data driven” as John’s are?

Cheers,

Dr. Ron

Shelf life means different things in different situations.  Post something on the internet and it will last forever.  Leave fresh fruit out on a hot day and it won't make it through the afternoon.

Jim Hisert recently wrote a blog post on Solder Shelf Life where he teams up with Eric Bastow to discuss Solder Shelf Life.  As they state, Solder Paste has a very defined shelf life because of the flux component.  The shelf life of Solder Preforms, on the other hand, is defined by the solder alloy's propensity to form oxides on the surface of the metal.

How do you minimize Solder Shelf Life issues?  There are several ways:

1) Order quantities that are reflective of your usage. It is attractive to get a large-volume price break, but you need to be able to use the product when the time comes.
2) Request that the solder preforms be packaged in quantities that you use them.  Getting a year's worth of preforms in one bottle may be cheaper, but the constant opening of the jar will only cause the remaining parts to oxidize and become unusable. If you consume 120,000 preforms per year, consider having your order shipped 10,000 pieces per month to assure a fresh supply of material.
3) Store preforms in their original, unopened containers, in a nitrogen dry box.
4) Once you have opened the jar, keep the lid on while it is at the work station.  At the end of the day, return the jar to the nitrogen dry box with the lid off so the nitrogen can purge the oxides that may have begun to form.
5) Consider tape & reel packaging.


 

上周我参加了2天半高强度，快节奏的IPC认证培训，对电子组装制造electronic assemblies 有了更全面的认识。  

IPC是电子电路组装制造这个大行业的北美组织。 我们平时说的J-STD-00X, 都是IPC的标准，可以说是行业标准了。现在很多OEM, ODM, 和EMS公司的电子组装制造，也是参照IPC标准。  在我们这个细分的焊接材料供应商市场中，关注最多的是J-STD-004, 关于助焊剂flux的标准， J-STD-005关于焊锡膏solder paste的标准，还有 J-STD-006 关于锡粉solder alloy的标准。 其中，J-STD-004(B) 和 J-STD-006(B) 都是最新的版本，大家可以在IPC网上直接购买。因为版权限制，这里也不方便和大家分享原版。 

JIS是日本JSA(Japanese Standards Association)的标准。 IEC(International Electro technical Commission)是多是欧盟的标准。很多总部在日本或是欧洲的电子制造商，都参考这两个标准。

当一个行业逐渐壮大了，所有相关参与者们聚在一起，就会制定/完善自己的行规行标。 当一个国家/地区的行业在全球的这个行业中，有足够的话语权(市场份额，地位等)，那么其它地方这方面的相关活动，也就要遵循这些标准。 在我们这个大行业中，日本有很强势的电子和电子组装制造公司，美国和欧洲也是。它们都有各自大同小异的标准。 中国作为世界加工工厂，为别人服务的话就要按照别人的规则办事了。 但是近年来，中国自主品牌的电子和电子加工行业，也日渐强大。或许，某一天中国也会出自己的标准(China RoHS就是一个很好的例子)？如果有这个需要和必要（经济利益的驱动）？ 翘首以待。   

Pic: http://www.sgmmgroup.com/web_images/ipc_logo.jpg  

PS: 当我上课的时候还在想工作的事情而开小差的时候，火眼金睛的老师总会冷不丁的叫我回答问题(cold call) “Anny, please answer this question!” …真是无语了。如果这里也流行“举手回答问题”，多好啊。  

Shelf life of solder is a concern that is raised by customers on a somewhat regular basis.  Solder pastes typically have a well defined shelf life, however the useable life of a solid form of solder may be much longer and harder to define.  This was the topic of one of my first blog entries, although I think Eric Bastow has a better explaination than I did. Here is Eric's explanation:

“One of the issues surrounding solid forms of solder (no incorporated flux) is determining the usable (or “shelf”) life of the solder. Solder manufacturers have to draw a “line in the sand” somewhere to establish a time limit on the duration of their “warrantee” period. For better of for worse, in our document driven world, many electronics manufacturers live and die by the solder manufacturers stated shelf life, and will even petition the solder manufacturer to recertify the solder after the shelf life has expired so that it can continue to be used. Otherwise, it is excluded from further use and discarded.

There are many solder alloys in existence and each alloy “ages” in a unique way. However, the most common issue with aged solder is oxidation. Is there a level of oxidation at which a solder is no longer usable? With normal storage and handling and use of a flux, the author believes that the answer may be “no” based upon the results of an experiment.

60In/40Pb spheres, 300 microns in diameter, were reflowed in air or nitrogen onto ENIG coupons with two different activity level no-clean fluxes; reduced activity ROL0 (passes J-STD-004A SIR un-activated) and ROL1. The spheres were oxidized to four different levels; fresh, 4 days at room conditions, 5 hours at 85C & 85%RH and 3 minutes of violent shaking. The appearance of the “fresh” was shiny; the “4 days at room conditions” and “5 hours at 85C & 85%RH” were very similar in their slightly dull appearance, and the “3 minutes of violent shaking” were noticeably darkened.

The experiment was performed with a reflow profile that had a peak temperature of 231C. After reflow, the diameter of the wetted spot was measured.

Interestingly, the determining factors were the flux type and reflow environment (air or nitrogen). For a given flux and reflow environment, there was no statistical difference in the size of the wetted spot among the different levels of oxidation.“

-Eric

Today I made my rounds in the office, collecting ideas for you from our tech guys  - ideas to help you speed the alloy and flux selection process.  The team gave me ideas from the start of the design process all the way up to speeding the order process, and all the steps in between.  These are solder basics, but they can help you get your process up on its feet quicker - if you put together a little information up-front:

1) Call a tech guy early, but be prepared by knowing the specifics of your material needs, like powder size, flux type, and any design requirements.

2) If you’re an engineer specializing in component attachment, get yourself involved with the component or board design team. It may mean extra meetings, but it will save many headaches in the long run after you help the team remember the meaning of “design for manufacture”.

3) Define the details of your application, equipment, and process before selecting a material. For instance, knowing the needle size that you will be utilizing in a dispense machine will speed the powder size selection for die-attach solder paste.

4) Be aware of cleaning requirements and your current in-house cleaning equipment and chemicals before choosing a flux or flux vehicle.

5) Understand the operational temperature of your assembly and the maximum processing temperatures of the components. This will make alloy selection much faster.

6) Don’t get hung up at the ordering process – know what size packaging you need. Do you have equipment that only fits a certain size syringe or cartridge?  Knowing this ahead of time will save you a second call to verify while talking with an Account Specialist.

7) For alloy compatibility and metallurgical considerations, be prepared to lets us know the composition and thickness of your surface finish. This will also save a second call, because it is required information in order for us to get you the right alloy and the perfect flux for your application.

8) For solder paste printing recommendations, know the specifications of the stencil you will be using. Aperture size, stencil thickness, and any other dimensions you can provide will help guide which flux vehicle and powder size we will recommend to you.

9) For preform selection, try using thinner preforms. For prototype situations you can stack the thinner preforms to build solder volume, and it is much quicker to order preforms in 1 thickness as opposed to many thicknesses.

10) Understand your process bottlenecks. By letting us know your material needs we can usually suggest a few materials, but perhaps one of those materials can help eliminate a problem that is slowing your process down.

11) Consider your company’s roadmap for the next 5 years. It doesn’t make sense to select a material and need to select a new one only a year later. Save yourself the time involved in a second solder evaluation and know what the future holds regarding safety/environmental concerns. Likewise, understand the roadmap of your supplier, their future materials, and how their current materials will fit your company’s future plans.

Conductive epoxy is a common material choice for bonding components, especially if the assembly process is temperature-sensitive. Tin-based solder paste or preforms with flux are preferred Pb-free bonding materials; however, conductive epoxies arguably provide advantages over these traditional solder assembly materials. 

It has been my experience that these advantages are perceived in the absence of an awareness of the full solder assembly materials product offering. Specialty solders can provide the same advantages as conductive epoxies and then some.   

Some claimed advantages to conductive epoxies include:

·         RoHS-compliance

·         Ease of assembly

·         No-clean

·         Low cure temperatures

Low-temperature solders such as 58Bi42Sn and 52In48Sn are specialty low-temperature solders which have these same properties including processing temperatures below 150ºC. Both of the referenced alloys are Pb-free, can-be used with no-clean fluxes and are assembled using the traditional solder assembly techniques.

It would seem a toss-up between whether to use a conductive epoxy or specialty solder to assemble temperature-sensitive components except that there are additional advantages to a soldered assembly as compared with an epoxy-assembly. These include:

·         Thermal cycling reliability

·         Solder material consistency

·         Reworkability

·         Thermal Conductivity

After a quick survey of a few of the technical service personnel in the office today, I put together a little snapshot of what is happening right now:

Amanda Hartnett and Ed Briggs are conferencing with an engineer that Amanda met at a local SMTA meeting.  This potential customer asked for product recommendations to improve their assembly process after they heard about Indium 8.9HF (a halogen free solder paste).

 


Brandon Judd is working on reducing voiding via profile modification with our flux coated preforms.

Mario Scalzo is tracking and organizing our technical team’s submissions to the Silver Quill program, where authors at Indium Corporation are recognized for technical papers and presentations.

Eric Bastow is helping a customer determine the best soldering materials for a medical application which involves soldering nitinol to nitinol. Common choices are using flux #2 or flux #3 with Indalloy 121 or Indalloy 182 – depending on the application.

And you’re reading what I’m doing right now. One interesting thing that I realized today is how we are working on very different things at the same time, both reactively and proactively. While some of us are fixing customer issues, others are helping to plan future processes to eliminate the need for a fix. 

Something that may not be apparent from this daily description is how this technical team works together. One of the nice things about being in the same office is that we can share ideas and learn from the experiences of our peers.  Even an office mate's tech call or brainstorm session can be a learning exercise. Working together gets us ready for your next call, so we can have the answer for you before it is even asked.

All the best
~Jim H

Click here for a description and video that shows a nozzle design from FINETECH  which clamps down onto PoP components during rework. 

“The PoP soldering head is an easy-to-use tool for reworking stacked devices as a whole in a single reflow process. It uses vacuum-actuated mechanical clamping tweezers which avoid separating the single layers of a PoP during component removal. The PoP soldering head can be easily adapted to different component thicknesses. Furthermore it is possible to adjust the width of the clamping tweezers prior to the process when the rework arm is swiveled down to avoid affecting other components on the PCB (e.g. accidental shifting of neighboring small passives).”

Sounds like this would be great for combating “PoP Quicksand”. That nasty problem that large components have when the vacuum provided by the nozzle isn’t strong enough to lift the package-on-package component back out of the PoP solder paste or dipping flux. Okay, I just made up that term – but it’s pretty descriptive, right?

Conceptually it seems to make a lot of sense, please comment if you have any experience with it!