Solder Preform

• Five Solder Families and How They Work (Eric Bastow)
• Solder Preform Basics (Paul Socha)
• A Quick Guide to Solder Preforms (Jim Slattery and Paul Socha)
• The Basics of Soldering (Chris Nash)

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

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

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

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

~Jim

Folks,

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

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

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

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

“I’ll see you there,” Patty said.

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

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

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

“Rob, what happened?” Patty cried.

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

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

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

Just then an MRI tech came.

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

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

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

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

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

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

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

“Sure,” Sarah said, “go ahead.”

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

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

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

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

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

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

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

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

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

At 4:30 PM another email arrived from Emily.

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

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

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

Folks,

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

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

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

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

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

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

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

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

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

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

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

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

“Precisely,” Patty responded.

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

Patty’s cell phone vibrated again.

“Exactly,” Patty commented.

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

“It is nearly perfect,” Patty said.

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

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

Patty thought this was something to discuss with the Professor.

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

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

Cheers,
Dr. Ron

上周是感恩节。根据美国的习惯，我们拷了一只火鸡Turkey来庆祝。

平时向客户们介绍我们公司的preform预成型焊片这一大产品系列时，我们经常会用这个有趣的故事：你们知道这个细条小圆柱形的焊片用在哪里吗？ 感恩节的火鸡里！其实是pop-up turkey timer。 在全美销售火鸡和火鸡测温器的厂家，都可以大量地使用我们这种低温合金的焊片。每年感恩节烤火鸡，大家会把timer插在火鸡里面，等火鸡里面也达到一定温度（熟了），在timer里面的低熔点合金(含有铋金属Bi/Bismuth)就会融化膨胀，使其里面的弹簧自动跳起来。

Bi58Sn42是一种很常用的无铅低温合金。它可以用在散热器heat sink/heat pipe的焊接上，也可以用在电路板的印刷焊接上。有些客户板子上的某些元部件有不能承受超过180⁰c 或是190⁰c(Sn63Pb37的熔点是183C,SAC305是217C)，所以就常会用到BiSn锡铋合金。或是分温度层(step soldering)焊接，也会用到这种低温合金。 锡铋这两种金属的价格虽然随着市场大宗商品价格的变动有些变动，但是和贵金属金银等相比，价格还算可以。

铋是一种很脆的金属，所以锡铋BiSn的韧性不够。但是如果加上1%的银，Bi57Sn42Ag1，就可以大大提高合金的柔软性和韧性了。

Cheers!



Pic: Google Image

PS: 上周我给加拿大的客户发邮件，不小心顺手写了祝感恩节快乐的语句。后来一点击发出后，就马上后悔了，因为我突然想起加拿大人感恩节不是在11月，而是在10月份。因为加拿大更加靠北边，他们的粮食收成季节早过美国，所以也提早庆祝感恩节…好在其中一个加拿大客户还挺幽默的，马上回复了我的邮件，祝我们这里感恩节快乐

Folks,

In addition to electronics assembly productivity, solder paste and solder preform applications, and other electronics assembly concerns, many of you know that I teach statistics and have been a life-long math nerd. So, I was intrigued when good friend Rick Short, alerted me to the New Orleans Saints football team being 0-11 for coin tosses this season. One naturally asks, how unusual is this result?

Assuming a fair coin, there is a 50% chance of winning or losing on each flip. The chances of losing two times in a row is 0.5 x 0.5 = 0.25. The chances of losing 11 times in a row, in the first 11 tosses, is 0.5^11= 0.00048828125. Or about 2000 to 1 ( 1/0.00048828125 = 2048) as the article points out. Wow!, seems unusual. However, there are 32 teams, and it has only happened to one team. So what is the likelihood of this happening to one team this year? This calculation is a little more tricky. The easiest way to calculate it is to ask the question, what is the likelihood of this event not happening to any team?

The chances of not losing 11 in a row, in the first 11 tosses, for any team is 1-0.00048828125 =0.99951171875. So the chances that none of the 32 teams would lose 11 coin tosses in a row is 0.99951171875^32=0.98449268023. The chances that at least one team might lose 11 in a row is 1 minus this number or 1-0.98449268023= 0.015507319766 or about 1.55%. This number is still quite low. But what if we looked a 50 seasons?

The chances that 50 seasons would go by and no team would lose the first 11 coin tosses in a row is 0.98449268023^50 = 0.45774601688. So in 50 seasons, with a 32 team league, the chances are 45.77% no team would lose the first 11 coin tosses in a row, or 54.23% that at least one team would. Since these odds are close to 50/50, in fifty years, the Saint coin toss loss string is a 50 year event.

The article goes on to state:

               “And while the Saints are 7-3 and lead the NFC South despite coming up short every single time on what should be a 50-50 proposition, coin-toss statistics — yes, they do exist — show that the NFL team that won the pregame flip wound up winning 52.1 percent of the time through Week 10 this season, according to STATS LLC.

That’s about the same as the 52.6 percent that STATS shows for coin-toss “victories” matching up with game victories since the start of the 2008 season, when the NFL changed the rules to allow the team that wins the toss to defer its choice until the second half.”

If there is interest, I will see I can calculate the statistical significance of this apparent coin toss win 2.6% advantage. My guesstimate is that the difference is quite statistically significant.

Note: Some readers may ask why I have used so many decimal places in my answers. Experience has taught me that when you are taking numbers to very high powers (the 32^nd and then the 50^th) that rounding errors can be great.  In addition, noticed that I often said the "first 11 coin tosses." The odds would be higher to get eleven in a row out of a larger number of tosses, say 16.

Cheers,

Dr. Ron

Folks,

Rob heads to Guadalajara to solve the QFN voiding problem......

As Rob sat on the airplane, he was excited to go to GDL (Guadalajara, Mexico) to help solve the voiding problem. He knew Patty would be a little peeved that he asked for Pete to come along, but she was gracious, recognizing that Rob would benefit from a success in this effort.

As the plane circled for a landing, Rob was preparing for the somewhat comical trip through customs. He always thought that the red light/green light method of determining if they were going to search you bags was unusual. Oh well, go with the flow.

The ride from the airport was about 40 kilometers to the factory through GDL’s bustling traffic. After arriving at the plant Rob was relieved to see that Miguel Mendoza was there to meet him and Pete. Rob had worked with Miguel in the past and respected him as a process engineer. Miguel told them that a kick-off meeting was scheduled with the site GM, a fellow from the US named Grant Wilson.

As the meeting started, Rob introduced himself to Wilson in Spanish.

“Wow,” Wilson chuckled, “when asked if I am bilingual, trilingual or American, I have to say I am American.” “But, I am taking Spanish lessons,” he continued.

Rob looked at Miguel and saw him roll his eyes. But Rob thought it was at least a nice gesture that Wilson was taking Spanish lessons.

“Perhaps someone could share what actions have been taken and what the status is,” Rob suggested.

“Miguel, could you give Rob an overview of where we are” Wilson asked.

Miguel began, “The warranty send back rate is 5% on Druid phones. Almost all of these failures have been traced to high powered QFNs that have significant voiding under the thermal pad. The voiding percentage is about 50-70%. About a week ago we obtained Derrick Herron, Dr Yan Liu and Dr Ning-Cheng Lee’s recent paper, Voiding Control at QFN Assembly, at SMTAI 2011.  We changed our stencil design, as suggested in the paper, to allow for venting of the solder paste volatiles and voiding went down to 30 to 50%.”

“What level of voiding would be acceptable?” Rob asked.

“We’re not sure,” Miguel answered.

“So it seems we have two issues, one is to determine if 30 to 50% voiding is OK and the other is to see if we can reduce it further,” Grant Wilson reasonably commented.

“My sense is that we need to be in the less than 30% range,” Rob added. “This may require that we use solder preforms. Voiding is caused by outgassing but also by insufficient solder,” Rob finished.

“OK, you two go and solve the problem and get back to me. You have 3 days,” Wilson commanded.

Rob, Pete, and Miguel headed off to get started on their assignment. Rob was really glad Pete was there.  He was an expert in setting up and optimizing the component placement machines that were at this site.  Fortunately, Rob had also brought some solder preforms with him, expecting that they would be required. A call to the QFN vendor confirmed that less than 30% voiding should be the target. Rob looked at the data and x-ray images of the work that Miguel and his team did to reduce the voiding by improving the venting of the flux volatiles. He was impressed. But he didn’t think it would be enough.

(Dialogue translated from Spanish)

“Miguel, I’m almost certain that we will need to use solder preforms on the two most critical QFNs,” Rob began. “There are two major reasons for voiding, the first is flux volatiles forming voids, the second is solder starvation. Most people don’t realize that solder paste is only 50% by volume metal. In cases like this, where we really need low voiding, often the only path to success is to use solder preforms to add solder metal,” he finished.

Rob then showed Miguel Seth Homer’s SMTAI 2011 paper Minimizing Voiding in QFN Packages Using Solder Preforms. This paper describes the process steps needed to achieve a successful QFN solder preform process. Rob and Miguel spent the better part of a day setting up one assembly line to assemble with the solder preforms using this paper as a guide. They assembled 100 phones and the voiding level was 10.5%.

Early the next morning, they met with Grant Wilson.

“By the smiles on both of your faces, I gather you were successful?” Wilson asked.

Rob went on to explain how they determined that solder preforms were needed. He explained the process and waited for questions.

“What do solder preforms cost?” Grant asked.

“They are about $0.02 (US) in quantity, but understand that your warranty cost per $200 phone is at least $10 right now (0.05x200),” Rob answered.

“Did you have to slow the process done?” Wilson asked. “I have been a fan of the work that you and Patty Coleman have done with The Professor, you have convinced me of the importance of throughput,” he finished.

“The Professor has pointed out that almost never is a line completely balanced. Your flexible placers were waiting four seconds for the chip shooters. We put the preforms on the flexible placer and tuned up both machines by optimizing the feeder placement. The cycle time is now 1.25 seconds faster for the 3 phone per PCB card,” Rob answered.

“I’m curious, what was the greatest challenge?” Grant asked.

“Rob pointed out that the correct placement of the preform on the solder paste deposit for the heat sink part of the QFN is critical. We needed to assure that the preform was pushed into the paste far enough to leave a ring of paste around the preform to assure good mating with the QFN.  We couldn't have done this without Pete, he really knows the placement machines,” Miguel answered.

Miguel then showed Wilson an image from Seth Homer’s paper that displays this situation .

“Guys thanks for the great work. I have to admit that I didn’t really know anything about solder preforms, before today. In certain cases it is obvious that they can be lifesavers!” Grant summed up the situation.

“To celebrate your success, I’m treating for dinner tonight at the Santo Coyote, let’s meet there at 7PM,” Wilson suggested.

“Thanks,” Rob, Pete, and Miguel said in unison.

Santo Coyote was Rob’s favorite restaurant in Guadalajara, but it was Patty’s too. Rob was a little sad she couldn’t join them.

 Epilogue: Three months later it was confirmed that warranty send back rate was approaching zero.  Miguel was promoted to senior engineer for his part in the solution to this costly problem.

Cheers,

Dr. Ron

Folks,

Let's look in on Rob:

Rob looked at the new photo of Patty and their twin sons Peter and Michael. What a handful those two 18 month-olds were. Just like their mother! Rob was still pinching himself that he was lucky enough to have Patty as his wife. Rumors were that she would make VP soon, and a few of his buddies asked him if her success bothered him. 

He would always respond, “Let’s see: beautiful, successful, athletic, fun to be with, great mother, and most of all she loves me. What’s not to like?”

Rob really meant it. He felt Patty deserved her success. One of her great assets was her high energy level. She went to bed at 11:30PM and was up at 5AM to run two miles, lift weights, shower, and then take care of the kids. Rob just couldn’t keep up on less than seven and a half hours of sleep. So he got up at 7AM. Rob had to insist that they have some quiet time each night after the boys were in bed, to talk and maybe even watch some mindless TV. But Patty would often sneak her laptop out to work while NCIS was on. Patty, the workaholic!

Rob and Patty spoke Mandarin at home one day each week and Spanish another night. The boys were picking up all three languages. It was amazing to both Patty and Rob as they watched this miracle.

Well anyway, Rob did have one thing up on Patty: math. Rob was close to a math genius and also good at writing software. He was the “go to” guy for math modeling and writing software for the math models. He even helped the Professor improve ProfitPro. Rob also wrote a program that could be used to design an SMT line for maximum throughput. The software could do what Arena did in hours of simulation, in seconds.

Rob was startled from his daydreaming by the phone ringing. It was Sam the site GM.

“Hey Rob, we need your help in our plant in Guadalajara. Can you come right down to discuss it?” Sam asked.

“I’ll be right there,” Rob replied.

Rob walked to Sam’s office with a feeling of exhilaration. It was always fun and exciting to be sent on a trouble shooting mission.

“Rob, thanks for coming right down. This issue is QFN reliability. About 5% of the Druid mobiles phones in our Guadalajara plant are coming back with some of the QFNs burned out,” Sam began.

“Sounds like a voiding issue under the QFN thermal pad,” Rob interrupted.

“Wow, you seem to know quite a bit about this type of problem,” Sam remarked.

“Remember how I pleaded with you to go to SMTAI,” Rob teased.

“Yep,” Sam replied.

“Seth Homer gave a talk on this issue at the show last week. It was a terrific overview of the problem. From what you described the connection may need more solder. We may have to use solder fortification preforms to solve this. Optimizing the solder paste printing process may not be enough,” Rob summarized.

“Well, go there and solve the problem. The warranty issues are costing us a fortune,” Sam commanded.

After a moment of contemplative silence, Sam asked, “Do you need anything?”

“It would be nice to have Pete come. He knows the people there and is well connected. His Spanish is also terrific,” Rob said.

“OK, no problem. Since you sleep with Pete’s boss, you can work out the details with her. I need you to go this week,” Sam said.

“No problem,” Rob said.

As Rob left the office, he was elated with his new assignment. He had to admit though, he thought it was unprofessional and a little annoying of Sam to say, “since you sleep with Pete’s boss, you can work out the details with her,” but it wasn’t the first time someone said this. Truth be told, Patty might be a little annoyed. She really depended on Pete.

Will Patty be angry at Rob for taking Pete to Guadalajara? 
Will Rob solve the QFN problem?
How does Patty get by on only 5.5 hrs of sleep each night?
Stay tuned for the exciting conclusion.

• High thermal conductivity (33W/mK)
• Higher melting point than SAC alloys (221C)
• Low tensile stress, so suitable for large die (5800psi)
• Excellent thermal cycling properties (-55 to 125C)

1.  Preform (a specially-shaped solder piece) with TACflux® used to hold the preform and die in place
2.  Solder paste, which holds the die in place with no extra materials added 
3.  Soft solder die-attach wire, a fluxless type of solder wire, which is melted onto the substrate metallization under an inert cover gas, and the die directly mounted onto the molten solder pool, then allowed to cool.

上来扫尘了！前段时间生了个大胖小子，所以从怀孕到破腹产，见识了很多美国先进的医疗器械，联系到平时销售工作中了解到的客户成品，有些感慨“原来成品长这个摸样, 是这样使用的”！幸运也好，或是有些“不幸”吧，成品用在了我身上。

在电子制造加工行业(Electronic Assembling Industry)，亚洲很多工厂都是在做high volume, low mix 的产品，特别是computers, consumer devices & communication发面。 美国和西欧的工厂，更多是做high mix, low volume, 比如说医疗器械。

医疗器械的产品，直接涉及到生命安全，而且大部分都是long life span的，所以对可靠性(reliability)的要求十分高。 这也使很多加工医疗器械产品的工厂对焊接材料的选择和测试要求很严格，特别是对焊锡膏(solder paste)。

大件的没有和人体直接接触的医疗器械板子，很多都还是在用有铅SnPb焊接材料，比如说我这次生产前使用的超声波测试仪，监视宝宝心跳和我宫缩的测试仪，都应该还是有铅板子。不过很多医疗器械的客户们都在密切关注着2014年RoHS2对这方面的要求；客户们也在密切做准备，评估无铅材料，来应对届时的变化需求。

和人体有直接接触的医疗器械，很多都已经是无铅了。 前段时间有个客户生产一种一次性心跳读数器heart rate reading device，板子的形状像一个很小的婴儿鞋子，只有成人手掌的1/4大小左右，而且十分薄。当时就使用了我们的SAC305 焊锡膏和solder preforms (预成型焊片)。据说这种携带型小仪器可以扣在衣服上读病人的心跳，读出的数据直接通过wi-fi传送到医院的数据中心进入系统；医生和医院就可以随时随地远程收集病人的数据……

世界人口在不断地增多，也在不断地老龄化(aging population)，这使对医疗器械的需要在增加。这应该是一个有前景的大行业，也希望大家都能享受到这些科技进步带来的便利，益寿连年。

Cheers!



Pic: Google Image

PS: 还是那句我喜欢的话“生命在于运动（一下）”。和身边很多孕妇朋友相比，我才发现原来自己从小坚持和热爱运动在怀孕和生产过程中帮了那么大忙，生之前那一天我妈妈还在感慨说我走路一小时都还是健步如飞的，哈哈：-）

Recent test results show that solder fluxes handle high reflow temperatures (>450°C), providing better-than-expected visual results of flux residue!  

Solder fluxes have not traditionally been used with AuSn, AuGe, or AuSi eutectic solder, because their peak reflow temperatures were very close to or above the flux activation range. An average flux activates at approximately 125°C and is not recommended for temperatures in excess of 350°C. Although AuSn solder melts at 280°C, peak reflow temperatures are recommended to be >300°C, nearing the maximum suggested temperature of flux. AuGe and AuSi alloys melt at 356°C and 363°C respectively, which exceed the documented flux activation range.

Since these alloys contain ≥80% gold and are resistant to oxidation, flux is not always necessary. Other methods have conventionally replaced the flux function, such as mechanical scrubbing, or forming gas purging. If these technologies are not available, or assembly speed is priority though, a flux may be required.

So I, along with my fellow engineer, Brandon Judd, sought out to test some of our best fluxes with Au alloys at these high temperatures. The result: Not all, but a few of these fluxes work extremely well up to temperatures as high as 450°C!!!

The reflow profiles used tested the extreme abilities of our fluxes:

·         Peak temperature 410°C

·         Nitrogen Purge

·         Time above liquidus: 137 seconds

·         80AuSn solder preforms 0.249” square x 0.002”

Some fluxes did what we expected- they charred and burned. They simply were not designed for this environment. 

Others, such as our TacFlux010® were very resilient at these temperatures. 

For more information about these test results, please contact myself or Brandon.

Happy Testing!!

Amanda

Solder starvation

• weak solder joint strength
• open solder joints
• intermittent short circuits
• reduced first-pass yields
• increased inspection
• increased rework
• field failures
• damage to your company's brand & image
• reduced sales and profits

• The single-thickness stencil is designed for the majority of smaller components, starving the few larger components of solder volume.
• High-use interfaces, such as connectors and USB ports, require extra solder - to assure their solder joints survive the constant use in the field.
• Smaller, more tightly compacted circuit boards don't allow for deposition of enough solder paste.

• You can add solder just where you need it without overprinting solder paste or working with step stencils.
• Preforms deliver precise, repeatable volumes of solder.
• Preforms can be added during your existing SMT process with existing pick & place equipment.
• Preforms eliminate the need for rework or hand soldering at the end of the process.

Power amplifiers and transistors come in many shapes and sizes. The performance requirements vary as well. Attaching them can be a critical aspect of your design.

Both Pb and Pb-free alloys can be manufactured as a solder preform with a flux coating.(Learn more)  Selecting the right alloy and flux coating can be crucial to meeting your void criteria.  

A high-tech SOLDERING solution might include NanoFoil®, which effects a solder joint while minimizing heat exposure to your components.

There are also thermal interface materials such as the HEAT-SPRING® which utilize the unique properties of indium to create a superior thermal connection, similar to a solder joint.

There are many different attachment methods available, contact me with your design parameters and we can find your solution.  

Folks,

Many people have been infatuated by the price of gold in recent months, but the price of silver has also skyrocketed. In 2000 silver was about $3.00 per troy oz. In the eight years that followed, its price grew to $15/oz. Today it is trading at over $41/oz! This price is almost an all time high, except for the time when the Hunt brothers tried to corner the silver market in 1980. The aberration of their efforts jolted the silver price to just short of $50/oz, but it settled down to $11 or so after the Hunts came under margin call and other pressures.

Unfortunately, the dramatic price increase today, does not appear to be an aberration. Although we may hope that it will soon drop to more historic levels, we may not have reason to expect that it will.

Although not as dramatic, tin and copper have experienced significant prices increases as well. The price of tin has doubled in the last year to $15/pound and copper has increased from about $3/lb to $4.50.  These metals are obviously key ingredients in critical electronic materials such as solder pastes, solder bar, and solder preforms.

In addition, oil, which is used for most organic electronic materials such as PWB resins, flip chip underfill, and epoxy fluxes, has increased to $110/bbl - approaching its all time high of $145/bbl.

All of these price increases have a significant impact on the electronic materials supply chain. Although we are used to price decreases in the cost of our mobile phones and PCs, at this point in time, the price of the materials that go into these devices will be increasing.

As one materials supply chain executive commented at APEX, “It’s not like we can be clever and somehow work around the price increase of silver and these other materials, we have to pass it on to our customer, or go out of business.”

At the time of writing, the price of silver (Ag) was approaching the USD$50/tr.oz. (Troy ounce) level, and threatening to go higher. With 1 Troy ounce being 31.1grams, this makes the cost of pure silver ingot close to USD$1.60/gram.

Image from goldsilveroz.com

Materials costs are therefore a major consideration for anyone using silver in any form. Naturally, we are now seeing a few Power Semiconductor packaging houses evaluating the possibility of moving away from silver-filled epoxies for die-attach. The alternatives they are considering include the adoption of solder paste (or solder in some other form: wire / ribbon / preforms) versus a silver-filled epoxy.

Here are some thoughts on the Power Semiconductor assembly pros and cons, based on using solder paste as an alternative to silver-filled epoxies.

Good news (+)

+   Reduced materials costs
+   Improved pot-life / shelf-life *
+   Improved high temperature thermal-cycling
+   Strong, metallurgical joint formed between leadframe (substrate) / joining material / die
+   Improved thermal conductivity
+   Faster throughput (more units per hour, UPH)**
+   Easy clean-up ***
+   Does not wick onto NiPd surface to cause poor wire bondability

 * Although it is true that solder pastes are stored under refrigerated conditions, they do not require the -40C storage that is typical of silver-filled epoxies. 

 ** The dispense of solder paste is very rapid and can be done using multi-dot dispense heads. It undergoes rapid temperature reflow, versus the slow cure needed for metal-filled epoxies, which can be up to typically 1-3 hours, depending on the volume of silver epoxy.

 *** Because the solder paste flux does not cure like a polymeric material,  tubing and other conduits for the solder paste are easily cleaned out using common solvents, or can be simply purged with flux.


  ==================

Bad news (-)

-   Capital costs #
-   Adoption time / new process learning ##
-   Needs a solderable die surface
-   Voiding increase ####

 # The main cost-drivers here are:

- Reflow: Specialty reflow equipment is required for high temperature solders, such as
Heller or BTU reflow ovens

- Cleaning: If wirebonding is required after the reflow process, standard cleaning equipment and cleaning chemistry (aqueous or solvent-based) will be needed to remove flux residues

- Gas: Forming gas (H2/N2) or simple nitrogen may be needed to assist reflow.

Note that increasingly, for clip-bonding (non-wirebonding) applications using the new ultralow residue solder paste Indium9.32, even cleaning may not be needed, as the residue has been found to be compatible with compatible with a number of molding compounds in the industry.

 ## By partnering with a company like Indium Corporation with many years of experience in die-attach soldering, the ramp-up time can be significantly reduced.

 ### A solderable surface is usually a sequence of Ti / Ni / (Ag or Au) plated layers. The thickness of the silver (Ag) or gold (Au) precious metal layer is usually limited to 100nm (0.1microns). Compare this to a standard silver-epoxy bond line thickness (BLT) of 0.5-2mils (12-50microns).

 #### Acceptable voiding of less than 5% of the total die area is fairly easily achieved with good quality substrates and die-finishes.

  ==================

In closing, I am indebted to my friend and colleague Sehar Samiappan (Indium Corporation Area Technical Manager - South East Asia) for his insights.

Contact me to discuss this further.

Cheers!   Andy

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!