Dr. Lasky's Blog

Folks,

A reader writes:

My company makes an electronic product that requires a 40 year shelf life. We assemble with tin-lead solder on FR-4 PWBs. The product is to replace older technology (i.e. 1960-70s), but has some newer components such as BGAs, SOICs, and PQFPs. The product will be stored in dry nitrogen at 70F.  We take great care in manufacturing, by cleaning, inspecting, and testing the end product.

My question is, do you know of any studies that would discuss the reliability of products stored or in use for 40 years?

My sense is that our reader will be successful, but his question is profound and hard to answer with confidence. The military would like their electronics to perform for that long, but realistically much of it is replaced every ten years or so. If you look at something like the B-52 bomber, which debuted in 1952, the electronics have been upgraded regularly. So there isn’t as much 40 year electronics experience as one might think. An exception being the IBM AP-101 computer. This computer was kept in service for over 30 years, because it served its function and had survived the rigorous and expensive military qualification testing.

However, anecdotal data might support optimism for 40 year shelf life. In a class I teach at Dartmouth, The Technology of Everyday Things, I have sought out some old transistor radios from the late 1960s and early 70s to show the class how this old technology works. Anytime I have every found an old device like this, they always work, unless the batteries have leaked inside the radio.

This question raises an interesting thought. Although those of us in electronic assembly are concerned with tin-lead and lead-free solder joint life, what about the modern devices inside the components? Forty years is a long time. How will the 3D-22 nanometer copper circuit lines in a modern microprocessor hold up over this amount of time? These circuit lines lines are so fine that the 22 nanometer width is only about 70 atoms.  In addition, copper integrated circuits are still a relatively new technology. I’m sure much accelerated life testing has been done on such circuits, but would such testing confirm 40 years of shelf or service life?

I would appreciate any thoughts that readers have on these questions.

Cheers,

Dr. Ron

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

Folks,

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

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

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

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

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

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

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

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

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

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

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

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

Cheers,

Dr. Ron

Folks,

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

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

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

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

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

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

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

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

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

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

Cheers,

Dr. Ron

Folks,

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

“What a treasure of information,” Patty thought.

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

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

“What a simple concept,” she thought.

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

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

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

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

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,

The Guadalajara (GDL), MX Chapter of the SMTA held their first meeting on November 9 and 10 at CETI in GDL.
Approximately 70 engineers from local companies attended. It was a great success. 

The agenda was:

November 9^th, 2011

0830-0900am    Registration and Exhibits Open

0900-0915am    Welcoming Remarks and Exhibition starts

0915-1045am    Inventec: “Reliability Assessment regarding Flux residues"

1045-1215pm    Sanmina-SCI: “Capabilities of a Failure Analysis Lab”

1215-1315pm    LUNCH

1315-1445pm    DEK: "Optimizing the Print Process for Mixed Technology"

1445 -1615pm   Vitronics Soltec: “How to Choose a Robust Configuration for Equipment
                          for Defect Free Soldering - Reflow, Wave and Selective”

1615-1745pm    KIC: “Fixing Reflow and Wave Related Defects as Well as How to Avoid 
                          Them in the First Place”

 November 10^th, 2011

0900-1030am    Sanmina-SCI: “Process development of 01005 components”

1030-1200pm    Indium: "Lead-Free Assembly for High Yields and Reliability."

1200-1300pm    LUNCH

1300-1430pm    Universal Instruments: "Tutorial on Failure Analysis"

1430-1600pm    Zestron: “PCB cleaning before conformal coating”

1600-1730pm    Kester: “Understanding Soldering Chemistries - Reducing Costly
                          Defects, Increasing Yields and Reliability.

I spoke on “Lead-Free Assembly for High Yields and Reliability." We had several raffles and gave away autographed copies of my book “The Adventures of Patty and the Professor,” which has just recently been formally published. 

As usual, I had dinner at Santo Coyote, one of my favorite restaurants, however my Mexican friends also took me to Sacromonte, claiming it had better food. They were correct. I was convinced to try chicken mole which I liked. It is tough to beat Santo Coyote’s ambiance, however.

I can’t cite data for this, but I am quite sure that GDL has the largest number of workers in electronics assembly outside of Asia. It is great news that they now have an SMTA chapter to help the local engineers network and continue to grow in their skills.  It was great to play a small part in this success, but most of the credit must go to Indium Corporation’s Ivan Castellanos who is chapter president and Kester’s Miguel Vazquez, chapter vice president.

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.

Folks,

Some time ago, I mentioned that I was working on a consensus of the status of lead-free/RoHS compliant assembly. My hope is to find data and facts that will support the consensus. I am making progress, but at this time I would like to share the subtopics in the consensus. Look them over and see what you think:

1.       Was/Is lead-free electronics/RoHS needed to protect the environment?

2.      Is lead-free solder easier and safer to recycle than lead-containing solder?

3.      How has the increased use of tin and silver affected their supply and price?

4.      How much did it cost to implement lead-free/RoHS compliant electronics?

a.      What is the cost adder to a typical lead-free product?

5.      What are the process challenges of lead-free assembly?

a.      Are these challenges being addressed?

b.      If so, how?

6.        What is the reliability of lead-free vs leaded electronics for commercial applications?

a.      E.g. 0C to 100C thermal cycle, drop shock

7.        What is the reliability of lead-free vs leaded electronics for harsh environment/military applications?

a.      E.g. -55C to 125C thermal cycle, other Mil stress tests

8.      What is the threat of tin whiskers, tin pest and other similar lead-free related reliability phenomena?

9.      What is the status and need for halogen-free assembly?

Help me by suggesting topics that I have left out.     
Contact info here.
Cheers,
Dr. Ron

Folks,

In a recent posting we discussed that the higher melting temperatures of lead-free solder require reflow soldering temperatures to be higher, thus more electricity is used in lead-free assembly. However, as we calculated, this increased use of electricity is very small compared to all electricity used in the world.

An additional concern that some have voiced is the claim that RoHS, with its lead-free requirement, actually makes the environment worse because more tin and silver is used in lead-free solders.   They argue that the increased use of these metals, creates mining pollution and has driven the price of these metals sky high. Let’s examine these claims.

Prismark has estimated that approximately 90,000 tons of solder are used in electronics, with about 80,000 used in wave soldering and 10,000 tons for SMT soldering. It is important to remember that electronics solder is a subset of all solder. All solder (alloys for brazing pipes etc) uses about 190,000 tons of tin. Solder is the single largest user of tin. See Figure 1. 

Figure 1. Solder is the largest end use of tin. Tin is the base material for almost all solders. 

If tin-lead solder were still used predominantly, approximately 57,000 tons of tin (90,000 x 63% tin) would be used annually. With lead-free solder, about 88,000 tons (90,000 x 98% tin) of tin are used per year. This is an apparent increase of about 30,000 MT of tin used each year. However, an interesting thing to consider is that lead-free solder is about 14% lighter than tin-lead solder. Knowing that, and knowing that solder used in wave soldering (remember wave soldering accounts for almost 90% of all solder used in electronics assembly) is consumed by volume not weight (i.e. assuming approximately the same fillet size), about half of this increase is canceled out. 

This is all a bit confusing however, so it may be best to just to look at tin use. According to the United States Geological Survey (USGS), about 300,000 tons of tin are mined each year. Figure 2 is a graph of world tin production at mines per year (this graph does not show recycled tin.)  The amount of refined tin used each year in the US is depicted in Figure 3. Figure 3 includes about 15,000 tons a year of recycled tin. Recycling solder is very cost effective. Scott Mazur just pointed out (Printed Circuit Design and Fab and Circuits Assembly, p 36, August 2011), that recycling solder dross is 10 times as cost effective as recycling aluminum cans.

Looking at these graphs, it is hard to say that the amount of tin used has gone up since RoHS. It would appear that tin use is likely more affected by the economy and that it is really difficult to see an effect from RoHS’s July 2006 enactment.

Figure 2. World Tin Production at Mines. 

Most wave soldering solders have low or no silver. So, about 3% of the 10,000 tons of SMT solder, or 300 MTs of silver, are used in electronics. This is about 1.5% of the 22,000 MTs of silver produced each year. Silver use in electronics does not make anyone’s list of top silver usage.

Figure 3. US consumption of tin has decreased since RoHS was enacted.

So electronics solder use since RoHS has not caused tin use to increase, nor is it a significant factor in silver use. Therefore it is highly unlikely that electronics' use of tin or silver has been a prime driver in their stunning price increases in 2011.

 Folks,

In gathering information on the status of lead-free soldering, some helpful friends pointed out two great sources of information: NASA and The Navy. NASA sponsored an impressive lead-free reliability investigation: "Lead-Free Solder Testing for High Reliability Project 1." This project is finished and the reports are online. There is a follow-on project: NASA DOD Lead-Free Electronics Project 2 which is currently underway. The Navy sponsored a project with ACI and the summary is here. I am currently studying these documents to help develop the consensus.  Some preliminary info follows:

Regarding -20^°C to +80^°C thermal cycling, NASA concluded:

“Under the conditions of this test, Sn3.9Ag0.6Cu (SAC) and Sn3.4Ag1.0Cu3.3Bi (SACB) were always more reliable than eutectic SnPb regardless of component type (CLCC, TSOP, BGA or TQFP).

It has been shown that conditions that highly stress the solder joints by maximizing the CTE difference between the PWB and the component will favor SnPb over SAC6. Conversely, conditions that minimize the stress put on the solder joints (e.g., compliant components such as BGA’s and/or a thermal cycle with a small delta T) will favor SAC over SnPb. The current test falls into the latter category and we can say with some confidence that the lead-free alloys tested will outperform eutectic SnPb under field conditions that are even less stressful than the -20 to +80^°C thermal cycle test conditions.”

For -55^°C to +125^°C thermal cycling, the conclusions were more cautious, likely because the data were mixed:

“The feasibility of using Pbfree solder alloys in place of SnPb solder alloys for new product designs was demonstrated under thermal cycle test conditions. Additional investigation and characterization of Pbfree solder alloys will be required as a segment of a Pbfree solder alloy implementation plan. The application/introduction of Pb-free soldering processes for legacy product designs is not recommended without extensive materials characterization and product design review.”

These results seem to be consistent with what others report, lead-free assembly produces good thermal cycle results for commercial-type thermal cycling, but the results are mixed for harsh environment thermal cycling.

Folks,

You may remember that more than a year ago there was much speculation that tin whiskers may be behind the Toyota unintended acceleration problem. At the time I spoke out because there was no data to support the speculation. Now there is data, Mike Pecht and his CALCE Team at the University of Maryland, found numerous tin whiskers in the Toyota brake assemblies of concern.

Although the tin whiskers were not implicated in any failure, their presence is cause for alarm, and action should be taken to address this issue. Tin whiskers should not be found in mission critical devices. Pecht’s team has an algorithm that calculates the risk from tin whiskers that are discovered. The risk is 140 per 1 million not high, but with a million or so Toyotas on the road, clearly this is cause for alarm.

As you may know, I live in Woodstock, Vermont.  Many friends have asked how we are doing after hurricane Irene. Personally, my wife and I escaped with no damage to our house and only a bit of inconvenience (no water for 5 days). The town of Woodstock suffered considerable damage, but was, on the whole, fortunate. Some of the neighboring towns had all roads in and out washed away. Route 4 between Woodstock and Rutland has numerous sections destroyed. The flooding was declared by the governor to be the worst disaster in Vermont history. The photo is from the Valley News. It shows a wooden pedestrian bridge built to carry supplies into Bethel, VT by foot. There is no passable road, even for ATVs.

Best,

Dr. Ron

Folks,

Recently I posted a note about a flurry of Technet posts in which I was misquoted regarding the status of lead-free electronics assembly.  Harvey Miller then weighed in.  I responded. And this in turn raised more comments.

All of this caused me to wonder, is it possible to achieve a consensus on the state of Pb-free assembly?  I think it might be and am going to try.  The main thing that I think is important in this quest is that any points for the consensus, or lack thereof, be supported by data and analysis, not emotion.

If you have a point to add, that is backed by data and analysis, please share it with me.  One of the things I hope to accomplish is to develop a list of references, that can be referred to to support the consensus.

Stay tuned for more info on this effort.

Cheers,

Dr. Ron

Folks,

An obvious disadvantage of lead-free electronics soldering assembly is that the oven must be hotter and therefore will use more electricity (versus 63Sn37Pb soldering). But is the extra amount of electricity significant? Bill O’’Leary claims that a typical SMT oven uses $7K of electricity a year at $0.072/Kilowatt hour (Kwh) or about 100,000 Kwh. That number strikes me as about right, as a household uses about 5-20,000 Kwh per year.

In the late 1990s there were 35,000 SMT lines in the world, at a 3% growth rate that would be about 50,000 lines now. So worldwide SMT reflow oven use would be about 5E9 KWhr (50,000 ovens x 100,000 Kwh/per year) world wide.  

With most heat loss be due to convection, the increase in energy use will be approximately proportional to the difference between the oven temperature and the room temperature (25C). An oven processing tin-lead solder would run at about 210C versus lead-free’s 250C. So the added energy for a lead-free oven would be about (250-25)/(210-25) or about 22% more. So if all assembly lines in the world are SMT the added energy use would be about 0.22x 5E9 Kwh = 1E9 Kwh. The cost of this extra electricity would be about $100 million (US) at $0.10/ Kwh. The electronics industry generates about $1.5 trillion in sales. So this added cost would be about 0.0067% of sales. Since world electrical use is about 150,000 E9 Kwhr per year, this increase is about 1/150,000 of all of the electrical use or 0.00067%.

So although more electricity is used, the increase is not significant to the value of the electronics sold or the total world use of electricity.

Thinking about higher temperatures reminds me that my Indium Corporation colleague Dr. Ning-Cheng Lee is presenting a paper this week on a high melting temperature lead-free solder based on a BiAgX alloy system. Higher melting temperature solders are often needed in what is referred to as a solder hierarchy. Solder hierarchies have solders that melt at decreasing temperatures in multiple soldering steps, starting with the highest melting solder.

Cheers,

Dr. Ron

Folks,

It was five years ago today that RoHS was launched, amid concerns that the world of electronics would collapse due to the many challenges of lead-free (Pb-free) soldering. Well, we have five years of field data with no “the sky is falling” lead-free reliability events. But, has it been just five years?

No. As I mentioned in a recent post, Motorola implemented lead-free soldering around 2001 to take advantage of lead-free solder’s poorer spreading.  Hmmmm,  so it has been ten years! Not too bad!

Well it is actually better than that. SnAg3.5 solder has been used for decades in both:

1.     Step soldering:  with a eutectic temperature of 221C, SnAg3.5 can be used as the step previous to soldering with Sn63 or similar Pb-Free solder. The principle is to solder first with the SnAg3.5 and then with a lower melting temperature solder. The second soldering step is performed at a lower temperature, therefore not disturbing the SnAg3.5 solder joint or bond. 

2.      Mid-Temp Pb-Free alloy:  when a solder that melts somewhat above the melting point of a “standard” solder alloy is needed, and it must be Pb-free, SnAg3.5 is often the choice.  The automotive industry has used SnAg3.5 in these applications for decades.

While I still agree that lead-free solders need some time and experience, especially in harsh environments, to establish acceptable reliability for mission critical applications, the experience with SnAg3.5 is adding to lead-free solder’s reliability portfolio.

This information came to light with the recent announcement by a major solder materials supplier that they would no longer supply SnAg3.5. But take heart, Indium Corporation still supplies SnAg3.5.  

Folks,

Here is an interesting turn of events related to the reliability of lead-free (Pb-free) soldering reliability. 

I was reminded recently by something Carl Sagan said, or, actually, did not say: Billions and Billions Although this term is strongly associated with him, he never said it. Sagan believed that this term was connected to him because Johnny Carson mimicked him and used the term.

 
Although not even close to being in Sagan's league, I find that I am now equally unfairly associated with the term,  "lead-free solder is a grand success." This came about in an interview by Rob Speigel, which he summarized in a blog post.

In reading Speigel's post, you will see that,  "lead-free solder is a grand success," is Rob’s term, not mine. Well, Rob's post resulted in a string of postings on IPC’s Technet .

One person opined:

Irresponsible statements like "lead-free solder is a grand success" should NOT be ignored. Those who make such statements in the face of all of the contrary evidence should be noted, and treated as motivated only by greed. Lead-free soldering certainly has been known for many "thousand$" of successes.

I have learned that it is not even worth the bother to refute such statements with those who make them. It may be a "grand success" for PhDs who contract to solder paste companies, but it certainly has not been a "grand success" to literally thousands of companies dealing with the reliability elephant sitting in the room getting larger by the day, and the associated fallout as a result.

Ouch!

Another shared:

I disagree with the stated and implied affect of RoHS, on PWBs expressed in this article. Lead free assembly reduces reliability by 50%. There can be no doubt about that. There are too many studies that confirm lead free assembly significantly degrades reliability. There are so many studies that demonstrate a reduction in reliability that Rod's contention is almost laughable. We are now faced with increased failures of copper interconnections and dielectric material due to high assembly temperatures. There is an increase in crazing that can support CAF, significant copper dissolution, and cratering in assembly, Switching to lead free in most HDI applications is a significant challenge. Lead free assembly has a profound affect by degrading PWB's organic component (epoxy) due the temperature required and copper interconnection and also the exaggeration of the z-axis expansion of the dielectric.

I have asked for copies of the many reliability studies referred to. No response yet.

Finally someone hit the heart of the matter:

I'm curious if "grand success" were Dr.Lasky's words or Rob Spiegel's editorializing. Lasky does mention the lack of long term results, and Speigel, in the comments,  enumerates a number of reliability problems. ISTM that neither truly believes  those words.

Correct!, Thanks. 

Here was my response that I posted on Technet:

Folks,

Pete is correct. I never said lead-free implementation was a grand success. These were Rob's words in his blog post. 

I have said repeatedly that adequate lead-free reliability has been demonstrated for consumer products like mobile phones, PCs, portable electronics with service lives less than 5 years. This level of reliability has been demonstrated in numerous studies and more importantly with field data. Vahid Goudarzi, of Motorola, stated that field reliability of lead-free assembled mobile phones has been equal or better than leaded assembly units. His data go back to 2001 (not 2006. Motorola started early for reasons discussed below).

 The reason Motorola shipped early with lead-free products is due to the fact that lead-free solder does not spread as well. Because of this poorer spreading, Motorola was able to decrease lead spacings without getting shorts, thus increasing the amount of electrical function in a smaller space. Since increased function in a smaller space is the defining attribute of portable electronics, the importance of this lead-free advantage cannot be overstated. Admittedly, lead-free's poorer wetting is a challenge in other regards, especially hole fill in wave soldering, but the Motorola Droid X2 could not be assembled with leaded solder, there would be too many shorts. Since the packaging density of the iPhone and similar devices is on a par with the Droid X2, I suspect this statement is true for most mobile products.

I have also repeatedly stated that lead-free reliability for long term service, mission critical devices has not been demonstrated. As a result, these types of devices should not consider lead-free solder at this date.

I regularly discuss these topics in my blog (http://blogs.indium.com/blog/an-interview-with-the-professor). The most recent post shows a striking photo of leaded solders spreading -which is too "good" for portable electronics.

Cheers,

Dr, Ron

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.