Indium Corporation Blogs

Folks,

I have often pointed out that SAC solder's poor wetting is both a curse and Godsend.  It is a curse when trying to fill a through-hole in wave soldering, and a Godsend when assembling close lead spacings as shown in the image (below). Indium Corporation colleague and friend, Mike Fenner (image below), pointed out that, when I say that, "SAC solder doesn't wet well", I should be saying, "it doesn't spread well". His explanation follows:

SAC is different from SN63, and I think it is helpful to explain the difference by making a subtle differentiation between wetting and spreading.

The way that solders spread and wet to a surface is a balance of competing forces. We have surface tension acting to make the molten solder shrink into a ball, and wetting forces trying to make it spread across the surface. Wetting is also the action of the solder dissolving into the surface to form an intermetallic. This intermetallic is essence of the solder joint. The balance changes with different alloys, surfaces, and processes.

Most people are very familiar with the way that tin lead solders behave - and that governs their expectations. The different balance in SAC means the solder tends to spread less for the same wetting and, therefore, can give the impression of a lower quality joint. This lack of spread is usually expressed as 'poor wetting'.

I would explain this by saying the “active ingredient” in both solder families is tin. SAC alloys have a ~50% higher concentration of tin than the Sn63 solder alloy. This gives them a higher surface tension which increases the balling (coalescing) force. At the same time, the less dilute tin, in SAC solders, dissolves into a surface faster. So the final SAC joint can have a well formed intermetallic, but not high spread. These relationships will vary with surface finish and, of course, flux chemistry and process conditions come into play, but that’s for another day. Meanwhile I hope this simplified explanation helps.

Thanks Mike!

Cheers,

Dr Ron

The solder image is courtesy of Vahid Goudarzi of Motorola.

There seems to be a growing trend to use a low-Ag or Ag-free solder alloy for Surface Mount Technology (SMT) electronics assembly, similar to what is commonly offered for bar solder, used in wave and selective soldering.

For through-hole performance, the strength and stability come from the entire barrel of solder, whereas it is usually the foot and heel fillets that give SMT solder joints their strength.

Lets talk about the other issue with using a eutectic solder alloy in SMT: tombstoning.  One of the benefits of using the SAC (tin-silver-copper) alloy for SMT and solder paste, is that it has a built-in plastic range, similar to that of Sn62 (62Sn 36Pb 2Ag).  It is this plastic range that prevents tombstoning, and takes into account the inconsistent heating of the solder across the part (which is the sole cause of tombstoning).  Switching to a eutectic alloy eliminates the plastic range and opens the door for tombstoning.

Any powder manufacturing issues, such as the inconsistent distribution of dopants throughout the alloy and powder matrix, takes a back seat to the surface mount reliability concerns. 

There are other alternatives, such as SAC0307 (99Sn 0.3Ag 0.7Cu)… But, with the price of Ag finally coming down, and a long history of SAC usage, we don’t think it’s going to be a major player.

Next time, we'll talk about the manufacturing and costs associated with low-Ag and Ag-free alloys. 

I hope this helps. Contact me with any questions.

最近越来越多的客户提到了选择性焊接Selective Soldering. 我之前对此了解比较少，所以特意问了同事们学习了一下，发现选择性焊接有以下几点：

---和波峰焊焊接(wave soldering)比较相似，通常在SMT贴片回流后。

---和波峰焊焊接的不同点在于，selective soldering不需要整个板子都经过solder wave; 而是有一个固定的nozzle，对需要焊接的那一小部分进行”wave” soldering

---选择性焊接(Selective soldering)是整个板子不用经过第二次温度剧增(thermal excursion)，不单单保护了板子 (reduce CTE mismatch)，而且保护了已经焊接在板子上的对温度变化敏感的原件。

---选择性焊接(Selective soldering) 和波峰焊焊接相比，一般使用较少量的波峰焊助焊剂(wave flux)和锡棒(solder bar)；但是有些选择性焊接的设备需要往pot里放实心锡线(solid solder wires)而不是锡棒。

Cheers!

 

Pic & Video:Youtube

 

PS： 谢谢同事Eric Bastow的分享。虽然用wave flux and solder bar少了点，影响了revenue; 但是实心锡线是比廉价的solder bar利润高出很多的产品，所以还好啦：-）

Folks,

It was Wednesday evening and I had just finished a brief pitch on applications of SPC  to a group of twenty. I was followed by Jim Hall,  he spoke of process mapping using SIPOC.  So did these folks have solder paste under their fingernails, or wave solder flux stains on their shirts, or, perhaps, a solder preform or two stuck in their pant leg cuff? None of these souls would have had any of this type of trace evidence of electronic assembly on their person. You see, they were all medical doctors and students at Harvard’s  famed medical school.   (I hope it is OK that the proud dad shares that my daughter Jessica is a colleague of these folks.)

Jim and I were presenting to the doctors, because they are interested in process optimization in the healthcare industry. The event was hosted by Dr. Andy Ellner.  He is a professor and doctor at the medical school and is a focal point for these process improvement efforts. I was introduced to him in the summer of 2009 by Dartmouth’s  new President Jim Kim. 

In November of 2009, Jim Hall, our colleague Larry Parah, and I facilitated Andy’s team in dramatically improving the prescription refill process in Brigham and Women’s Hospital Clinic.  Jim and I plan on working with Andy in similar efforts over the next year or two.

The most striking thing that Jim and I left with on Wednesday evening was how profoundly interested these doctors and students were in healthcare process optimization. The Q&A session lasted nearly an hour.

Ah, yes, would that our many colleagues in electronic assembly were as interested in optimizing their processes!

Cheers,

Dr. Ron

The image is the front of Harvard Medical School

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

OK - your turn. Please comment.

The "wave soldering flux deactivation temperature question" arises every few weeks, and the easy answer is that wave solder fluxes are designed to see the temperature of the wave.

Now, in order to pass SIR testing, the test boards with the wave fluxes are sent through the wave pattern up, not in direct contact with the molten alloy. They still see the majority of the heat from the wave.

The “deactivation” temperature varies from process to process because of the differences in board complexity, flux application, and preheat, as it is really a matter of total energy input, rather than a specific temperature.

The potential for reduced SIR is the main issue, not necessarily ECM or corrosion.  With a rosin-free flux, there may be some visual clues, as well. If you see that the flux has dried to a white, powdery residue that may be a sign that it had not seen temperatures.

We get this question mostly from corporations that believe they can use the same flux formulation for wave soldering and hand assembly / rework. Wave fluxes are not designed for hand soldering, and will more than likely cause some sort of downstream issue if used as such.

Feel free to ask me any questions about your process!  From One Engineer To Another!

I just received a customer inquiry regarding a phenomenon that is little studied and even less quantified; “How many times can I reflow a solder alloy before damaging the solder joint?”

As you may already know, each time you bring a solder alloy above its liquidus temperature, it continues to dissolve the metallizations on the substrate to which you are soldering, as well as the metallizations on the leads of the component being attached. With modern processes, a 3-time “excursion” is common, especially with double-sided reflow and rework. Typically, the solder applied with paste is not reflowed again during the wave, because, through the use of pallets or selective soldering, it doesn't get quite hot enough to melt. That said, in such a case, the solder joint may become hot enough to receive some damage. To me, the most interesting thing with crystalline intermetallic layers, is that they don’t need to reach liquidus to form larger crystals. So a temperature excursion close to the liquidus may also increase the crystal structure size.

Another factor is surface metallizations, especially easy-to-solder surfaces such as gold or HASL. With gold, molten Sn/Pb solder at 200°C will dissolve at 35u-inch/s. So, a fine flash layer, such as 3-5u-inch, is gone within the first second, and the actual intermetallic is formed to the underlayment; most commonly nickel (Ni). This is similar with HASL, as the HASL layer is consumed into the solder joint at liquidus, and the intermetallic layer is formed with what is beneath the HASL.

The intermetallic layer will increase with time above liquidus (TAL) and also with temperature, with hotter dissolving more of the surface. This is why there are operating temperature limitations on the final solder joint, such as no more than 90% of the solidus of the alloy, in degrees Kelvin.

Another factor that affects grain structure, besides TAL and peak temperature, is cool-down rate. A faster cool-down rate will form a smaller crystalline grain structure, but keep in mind that a too-fast cool down rate may result in stresses being trapped in the grain structure from the CTE mismatch between the component and the substrate.

It has been our experience that 3 temperature excursions is the accepted limit (by most companies that I work). But, the only recommendation that we can offer is that you try “worst-case” scenarios, and have ALT testing and SEM cross-sections performed on real-world products in which 3, 4, and 5 excursions have taken place. Your particular case may be unique - it is well-worth determining your particular situation.

Folks,

Answers to the quiz of a few weeks back......

Phil and Rob had agreed to ask the GM if it was OK to ask the tech and engineers at some of their subcontractors to take the test anonymously. Over a period of two months Phil and Rob got 52 people to agree, almost all of them after Phil or Rob agreed to take them to lunch. They asked Patty to grade the “exams.” Today Patty would reveal the results.

“Phil, this is one of the best bets I have ever made,” teased Rob.

Everyone at the lunch table chuckled, but the look on Phil’s face said he expected to lose. Rob has said that he thought the average score would be less than 70%, Phil insisted that it would be greater than 85%. In asking the different folks to take the test, invariably Phil started asking questions not on the test. He was surprised that no one knew what tin pest was. He even asked how to time balance a chip shooter and flexible placer, only one in twenty knew.

As Patty approached the lunch table, the ensemble held their breath.

“OK, Patty, tell us the bad news,” Phil said in a resigned tone.

“Rob wins, the average score was 58%,” Patty said getting to the point. “Here are the answers and percentages on each problem,” she went on:

1.    What is the composition of SAC305?
96.5% tin, 3.0% silver, 0.5% copper. 60% got this right.

2.     What are tin whiskers?
Tin whiskers are metal whiskers that can “grow” from tin plating on component leads. They are mitigated by 2% bismuth in the tin, a nickel overplate of the lead copper, a matte tin finish, and a few other mitigation approaches. 40%.

3.     In a stencil aperture, what is the area ratio?
The ratio of the area of the aperture opening divided by the area of the side walls. This ratio is typically used for circular and square apertures. It is equal to D/4t, where D is the diameter of square side and t is the stencil thickness. 40%

4.    What is an approximate peak temperature for a reflow oven in lead-free assembly?
Any answer 235 to 250C accepted. 90%

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.
b 70%

6.     What are local fiducials on a PWB for?
Local fiducials are located near the pads of a component with fine lead spacings to assure accurate placement. 70%

7.     What does "thixotropic" mean in regard to solder pastes?
The viscosity decreases with increasing shear stress. Hence, during printing the viscosity drops as the paste is forced through the aperture, aiding good aperture fill. It increases as the printed deposit rests, minimizing slump. 20%

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?
300/36000 = 1/120 hr = 30 seconds. 90%

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?
The amount of time that the belt needs to cover 40 cm is 40/100 = 0.4 minutes = 24 seconds. This is the minimum cycle time the oven can support. 40%

10.   What is "tombstoning"?
Tombstoning is observed when a passive component's terminations experience unequal wetting forces which are strong enough to lift one end of the passive so that it looks like a tombstone. 60%

Overall average score 58%.

“Wait a minute Patty, your answers are too demanding,” Phil shouted.

“Calm down Phil, I gave full credit for anything close,” Patty responded.

In unison, almost everyone at the table sighed “Yikes.”

Patty interjected, “One person who received a 70% commented after completing problem 9, ‘I didn’t think I would need a PhD in math to do this quiz.’ “

All agreed that organizations like the SMTA and IPC were more needed than ever.

Cheers,

Dr. Ron

Welcome! I am a chemical engineer experienced in an R&D setting and jumping into a new position in marketing here at Indium Corporation. Initially, in this blog, I will focus on my journey getting started, learning all the new facets of the business here, and transitioning from my former R&D mindset into something more outward facing and communications-based. I am relatively new to this world of social networking too, so I’m sure there will be plenty of growth in that direction as well. Hopefully, you will enjoy taking this journey with me, learning vicariously. I would certainly appreciate any pointers from you. 

Officially my job title is “Product Support Specialist”.  I’m learning that it means a lot of things, for example, being an expert in PCB assembly, the different products that are used for PCB assembly, and being able to convey that useful information to everyone that is interested. “Everyone” really could be anyone in this case: existing customers, potential customers, customers that haven’t even thought about how solder paste or another product might make their process easier, people who just have an interest in electronic materials… and people here at Indium, R&D, production, our sales team, and the list goes on. In time this blog (with any luck) will be a good resource for a lot of helpful information to all of these people.

As I am completing my first week here at Indium, I am feeling very optimistic about my new position and my capacity to contribute. Overall, this week has been like riding a wave of information, and just trying to scoop up as much as I can. I have been surprised by how much my previous experience in electronics materials is helping me. Even though the materials here are significantly different, I have been exposed to a lot of the same processes before (screen printing, mixing, metal powders, etc.), so I just have to make the mental links and note the differences. For instance, I was fascinated, while touring one of our manufacturing facilities yesterday, that we are using the same mixer I used in my former company’s pilot lab, just about 20 times larger. Also, we are packaging some of the material in the same cartridges and syringes I had previously filled by hand on so many occasions.

 

On a more personal note: Before starting Monday, I had mostly been filled with a sense of gratitude for having found a job that I really love, and a little bit with some apprehension about fitting into a new role, living up to all of the expectations (from myself, my co-workers, my new boss…). I suppose a long period of searching for employment, with all of the probing and feelings of rejection and such, really does change one’s perspective of their competencies. It has been difficult in the past months listening to the news and hearing reports of unemployment numbers staying the same or getting worse, and in addition having benefits for unemployment on shaky ground. In some ways it felt like people who were still employed might not understand how difficult it can be to find a job, even a job that doesn’t live up to the expectations one might have had 5 years ago. I just thought that I should note that there is still very much reason to hold on to hope: it is possible to find a wonderful job that fits your qualifications, and continue on after all of this economic turmoil. What was most important during my time searching was to keep searching for that job that would further my career the way I wanted it to, to keep applying to positions that might seem out of reach at the time, and to not get discouraged, because despite all of the unanswered emails and resumes, only ONE needs to come through… and that one could be awesome. Since Monday, of course, my doubts have been fading quickly, and I am still filled with that sense of gratitude, which I don’t think I would have appreciated without having gone through these tumultuous times.

 

前段時間和Indium公司研究波峰焊助焊劑的Jim Hevel一起出差，進一步了解了波峰焊助焊劑這種產品。 雖然電子產品組裝的焊接技術從波峰焊技術(wave soldering)到表面裝貼(SMT)轉變以來，波峰焊助焊劑從使用比率來講是少了；但是因爲整體的市場在增大，通孔焊接技術還是具有一定成本的優勢，某些特殊元件的焊接需要，還有部分簡易產品和不需要微型化的產品等因素，通孔焊接技術還是存在並佔有一定市場的。那麽波峰焊助焊劑也一直在業界被廣爲使用。

在波峰焊技術的焊接過程中，大家最關注可焊性(solderability)兩方面的問題：Hole Fill & Bridge.  良好的爬錫/填充孔，還有不要出現橋接現象。Jim說他在設計公司系列波峰焊產品的過程中，除了根據客戶要求和行業IPC規定外，solderability就排第一位了。請看以下表格。

適應市場無滷化的需求，Indium公司有酒精基(Alcohol based)和水基(VOC-Free)的無滷波峰焊助焊劑。

Cheers!

Picture: Jim Hevel with Indium Corporation

PS: Jim來自Indium公司的芝加哥工廠。剛好Jim在西雅圖那兩天，棒球賽是西雅圖水手隊對決芝加哥白襪隊(Baseball, Seattle Mariners VS Chicago White Sox)，西雅圖主場。Jim第二天問我有沒有看球賽…不熱愛棒球的我當然什麽都不知道。 經過Jim給我的棒球知識補充，讓我豁然開朗！怪不得某一個客戶曾經問我支持哪個隊，當時我心裏還嘀咕要不要請他一起看棒球呢…現在回想，人家只不過以爲你是“當地人”，肯定知道當地的球隊，找你侃侃對球隊的看法而已，哈哈。

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

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

So, I figured while I'm at 30,000 feet in an airplane on free wi-fi (how long have we waited for this? Thank you AirTran®!), it would be a perfect time to make a few comments about bonding with NanoFoil® and the role that pressure plays in the NanoBond® process.  Get it? Pressurized cabin?  Bonding pressure?

If you remember the basics for a second, NanoFoil, whether it is standard or plated with tin solder on both sides, needs to be in intimate contact with the surfaces to be soldered.  Once the NanoFoil is activated (at a thickness of 40 microns) it only stays at 1,500 degrees Celsius for less than a millisecond.  So, if the NanoFoil is not in "intimate contact" with the interfaces that need to be soldered (or "wet"), it will not create a great bond.  By applying pressure, you, the engineer, can maximize contact with the foil. The best way to do that is to use constant pressure and some foam or compliant material.

Constant Pressure: If you were to personally witness the NanoBond process (imagine you are shrunk down to nano-size and can actually see the NanoFoil reaction begin), you would see a wave of molten solder propagating across the bond area as the reaction occurs.  Now, if you were using two static plates to press the assembly together, there would be minimal constant downward pressure while the solder is molten. However, if you were using a spring-loaded, air-driven, or piston-driven pressing device, you would ensure that downward pressure was pressing the assembly together, enabling the molten solder to produce a high quality, low void bond.

Foam (Compliant Material): If you remember nothing else about this flight-induced blog post remember this:

A COMPLIANT LAYER SPREADS THE LOAD EVENLY AND 
HELPS TO MAKE THE MOST SUCCESSFUL NANOBOND. 

It shouldn't be too much of a surprise to learn that, if you use some foam above your component as you are applying pressure, the load will be spread much more evenly.

Well that is all for now. Preparing for a landing. Not me, the pilot. All I have is this wi fi compatible laptop!

Image source.

Folks,

After my recent post on the fact that there was no data linking tin whiskers to the Toyota sudden acceleration issues, there continue to be more posts saying things like “Tin Whiskers Implicated in Unintended Acceleration Problems.”  Many of these posts link back to the earlier TechEye post.   The basis for all of the posts, is a paper written by EurIng Keith Armstrong .   Armstrong’s paper is titled: “Toyota ‘sticking pedals’ recall is a smokescreen, Their sudden unintended acceleration problem is caused by electronics either due to EMI, lead-free soldering or software ‘bugs.’” It does not appear that Armstrong’s paper was sponsored or refereed. 

Since it appears that this entire wave of reporting implicating tin whiskers, in this important issue, emanates from Armstrong's paper, it is helpful to quote his entire comments on Tin Whiskers:

            "9.0 Lead-free soldering:

In recent years, various countries and trade blocs (including the European Union) have banned the use of lead on electrical solder, on the basis that lead going into landfill when electrical and electronic products are disposed of is bad for the environment, and hence for people.

But many accuse them of being shortsighted – lead has been added to solder in quite large amounts for many decades because it made the other main constituent, tin, behave much better, considerably improving reliability.

Now that lead has been removed from solder, which is now mainly tin (with a little silver and copper added) all sorts of new possibilities arise for short-circuits and open-circuits, and intermittent shorts and opens, mainly on printed circuit boards (PCBs) and mainly associated with small-footprint integrated circuits (ICs), especially ball-grid arrays (BGAs).

Its really just another cause of intermittent or fixed short-or-open circuits in electronic PCBs and modules - but one that would not have been any problem until a few years ago, and so could have caught Toyota by surprise.

John R Barnes has created a monumentally huge library of references to the problems of lead-free soldering, especially tin whiskering, see www.dbicorporation.com/rohsbib.htm. Prepare to be totally overwhelmed!

Removing lead from solder has the following effects:

9.1 Tin whiskers

These will grow out of soldered joints and can contact other conductors, causing short-circuits between PCB copper traces and the pins of connectors. They are often no longer than 0.5mm (about 1/50th of an inch) but can grow to 1mm (about 1/24th of an inch) or longer, especially in damp conditions.

Even at 1/50th of an inch they can short between the pins on a modern integrated circuit (IC). And the process of removing the PCB for inspection can brush them off, so you never find them.

And if you didn't accidentally brush them off, they are so thin they are very hard to see - you need a powerful microscope. They are as fine as the finest spider-web threads, yet can carry sufficient current to short-out the electronics. You won’t see them unless you are looking for them.

Being so thin, they can wave around in the breeze and/or due to shocks, vibration and acceleration, causing intermittent short-circuits.

The iNEMI organisation has published guidelines (www.inemi.org) on how to ensure that tin whiskers don’t grow too long, but I don’t know to what extent these are followed by suppliers of electronics to the car industry in general, or Toyota in particular."

Note that, in this paper,  there is no data or any evidence re: tin whiskers discussed from investigating any of the vehicles in question. All of this paper is an opinion.   In addition, the title of Armstrong’s paper leaves no room for any other cause, it has to be electronics or software. This position is very strong indeed for having no supporting data.

More recently Bob Landman added these comments to the tin whisker discussion:

“the increased use of electronics in automobiles when mixed with RoHS can make for a deadly cocktail. We don’t know what the causative agent [in regard to the Toyota recalls] was, but I have heard recently of new autos showing up at dealers that will not start. That cause has been linked to tin whiskers.”

Bob heard this. There is no report and no data. Until Bob gives us a reference for some analysis and data, his comments are little more than hearsay.  I searched the web in vain to find information related to Bob’s quote. In addition this comment is a little surprising, tin whiskers are usually associated with a certain amount of aging, hence not usually found in new products.   

That tin whiskers exist and cause failures is irrefutable. NASA  has an excellent website related to tin whiskers and failures caused by them. However, the total number of tin whisker fails reported is less than 100. Many other types of electronic failure modes would appear to be much more common.

My purpose of writing this post is not to suggest that tin whiskers are not a concern in lead-free electronics. However, it is a fundamental principle in engineering and science to only make pronouncements on how something failed, when they can be supported with data. No data supports implicating tin whiskers in the Toyota incidents. It is also troubling how readily many people referenced the work of Armstrong without apparently reading what he said and checking his sources and lack of data.

Cheers,

Dr. Ron

The image is from: http://nepp.nasa.gov/WHISKER/photos/ziff/ZIFF-whisker-3.JPG

I work for a company that manufactures solder, so I have a pretty keen eye for it. Even so, it’s still hard to tell a Sn/Pb ingot of bar solder from a Pb-free bar at a glance. The best way to keep these solder alloys separate at your facility is to have a good storage/tracking system and to have them made in different shapes. These pictures depict 2 lots of solder ingot, one is Sn/Pb and the other is Pb Free. Notice the physical difference of the two. This is a fail-safe, in case the ingots are misplaced or left untracked at your facility. Of course, this isn’t anything revolutionary – but perhaps an way to easily add an extra measure of safety into your wave solder process.

In my last post, NanoFoil Basics: Activation Part I, I talked about NanoFoil(r) activation properties (remember, I'm not using the term " ignition" because it implies burning, NanoFoil activation is more of a localized flash of heat), and some various ways to ignite the NanoFoil.  To review a bit, the two easiest ways to ignite the NanoFoil are by thermal (a heat source) and electrical energy (a spark).  Mechanical will work, but it requires a very concentrated impact which is very difficult to use or reproduce.

Don't Play Laser Tag with NanoFoil
The last way to activate the NanoFoil is through the use of a laser.  Now this makes sense right?  A form of high energy, very localized can ignite the NanoFoil.  Where it gets tricky is that a laser can also be used to cut NanoFoil as well!  I won't go into the gory details here, but with tweaking of the pulse width and power, a laser can either cut through the NanoFoil to make intricate shapes OR it can ignite the NanoFoil.  There are great processing implications for being able to ignite foil with a laser.  In automation, for example, a laser could be built into a head fixture that simultaneously deposits the NanoFoil, appiles pressure and ignites.  Additionally, having a through hole on the backside of a board where the component sits can give a sightline for activation with a laser.

Activation Tools
The easiest and cheapest way to ignite foil is with a 9 volt battery.  By hooking up wires to the leads and touching both leads to the foil (essentially shorting the battery and generating heat) you can activate the NanoFoil.  In demonstrations we have also forgone the leads and simply touched the leads of the 9 Volt to the foil.

American Beauty - The most common small production level tool used by customers and here at Indium is the American Beauty resistance soldering tool.  With this tool one lead can be grounded to a press or the part, and a secondary probe can be used to complete the circuit by touching the NanoFoil. Simple, easy, reliable and fits onto a table top, perfect for small scale manufacturing needs.



MPIS (Multi Point Ignition System) - Primarily used for sputtering target bonding with NanoFoil.  For sputtering targets larger than 6 inches, the NanoFoil needs to be activated in multiple locations to reduce voiding.  This needs a full blog post to explain the in-depth details, but the basics are as follows: when the NanoFoil is activated under pressure between two layers of solder, at the wave front of the NanoFoil is molten solder.  If the NanoFoil is activated at one location for a large part, the wavefront of molten solder will spray out the opposite side of the activation causing voiding.  If instead the NanoFoil is activated at opposite points around the part, the wavefront of molten solder meets in the middle and causes minimal to no voiding. 

ESD Sensitivity
A lot of times we get asked: is the NanoFoil ESD sensitive? It is a logical question, with a reactive material that last thing you want is an operator shocking the NanoFoil and activating it.  We have had the NanoFoil sent through standard ESD question, and the company responded in true engineering fashion: "The operator would have to have enough electrostatic energy running through him to kill him 10 times over before the NanoFoil would go off"  And so the short answer is no, the NanoFoil is not susceptible to ESD!

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

Note:  The golf photo is from: http://www.flickr.com/photos/gusilu/2785690627/sizes/l/#cc_license.

The "mudas" image is from: http://www.vision-lean.com/wp-content/uploads/2008/06/muda.png

Many consumer electronics transitioned to Pb-Free 4-5 years ago.  However, there are still a substantial number of electronics being built with Sn/Pb solder.  As some of these products begin to transition to Pb-Free, the decision on a bar solder alloy for the wave soldering process is a challenging one.  There are two widely recognized options to choose from:

• use SAC305 and keep the alloy the same as the SMT process
• choose a low silver (Ag)/Ag-free alloy which is substantially lower in cost

From a cost perspective the Ag-Free alloys are 40-50% cheaper than SAC305.  This is a substantial savings when you consider that solder pots hold around 1,000 lbs of solder.  In this arena, Indium offers our Sn995 which is a cobalt doped Sn/Cu alloy.  In addition to being lower in cost, Sn995 produces shinier solder joints than SAC305.

It would be great if that were the whole story, but there are cases when SAC305 should still be considered as a bar solder for wave soldering processes.  One advantage of SAC305 is that it has a faster wetting speed than any of the Ag-Free alternatives.  This can help when you have a board or process that is challenged with poor hole fill.  The chart below shows the difference between popular Pb-Free alloys for wave.

Another potential advantage of SAC305 is in thermal cycling reliability.  Because the typical wave solder joint is large and very robust, reliability may not be a concern for many consumer products.  However, as the reliability requirements increase for industries such as automotive, aerospace, and military, the stronger SAC305 solder joint may be what is needed to meet more stringent reliability requirements.

Both SAC305 and Ag-Free alloys, such as Sn995, have their place within the electronics manufacturing arena, but it is essential that the correct decision is made based on the product being assembled.