Tag Archives: Head-in-pillow

Lead Free 2015

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It is hard to believe that in July we will celebrate the 9th anniversary of the advent of RoHS. So the timing seemed right when I was recently asked to speak at the Boston SMTA Chapter on The Status of Lead-Free 2015: A Perspective.

An overview of the entire 75-minute presentation would be a bit long, so I am going to discuss three of the “questions” that I covered.

  1. Q: We are now almost nine years into RoHS’s ban on lead in solder. How has lead-free assembly worked out?

A: Something over $7 trillion of electronics have been produced since RoHS came into force, with no major reliability problems. One senior person, whose company has sold hundreds of millions of lead-free devices since 2001, reports no change in field reliability. The challenge that implementing lead-free assembly placed on the industry should not be minimized, however. Tens of billions of dollars were spent in the conversion. In addition, failure modes have occurred that were not common in tin-lead assembly, such as the head-in-pillow and graping defects. But assemblers have worked hard with their suppliers to make lead-free assembly close to a non-issue. Some people ask how I can say that lead-free assembly is close to a non-issue. My office is across the hall from some folks that purchase millions of dollars of electronics a year for Dartmouth. Several years ago, I asked them how they feel that electronics perform since the switch to lead-free. They answered by saying “What is lead-free?” If people that buy millions of dollars of electronics have not even heard of lead-free it can’t be a big issue.

  1. Q: In light of sourcing difficulties, is there an industry consensus regarding lead-free conversion for military, medical, aerospace etc. assemblers that will continue to be exempt?

A: The main issue is getting components with tin-lead leads, especially BGA balls. Many assemblers are reballing BGAs, which has become a mature technology, although with an added cost. As years go by and there becomes more confidence in medium to long term lead-free reliability, some exemptees may switch to lead-free. However, I think mission critical applications with 40-year reliability requirements must be extremely cautious to make the switch. There may be subtle reliability issues that may show up in 40 years, that are not found in accelerated testing. One concern is aging. Even at room temperature, solders are at over 50% of their melting temperature on the absolute scale (300K/573K = 0.52). So aging can occur at room temperature. Some research suggests that lead-free alloys may be more affected by aging than tin-lead alloys.

  1. Q: It has been said that you claim that lead-free assembly has some advantages. Can this be true?

A: Guilty as charged. Lead-free solder does not flow and spread as well as tin-lead solder. This property can result in poor hole fill in wave soldering and some other assembly challenges. However, this poor wetting and spreading means that pads can be spaced closer on a PWB without the concern of shorting as seen in the image below. Your mobile phone would likely be bigger if assembled with tin-lead solder.

Lead-free solder does not flow as well as tin-lead solder. Hence, closer pad spacings are possible.

 

Cheers,

Dr. Ron

Photo courtesy of Vahid Goudarzi.

 

Reducing Conversion Costs

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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 or BGA warping during reflow, and, occasionally, 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 Mr. Madigan, I’ll do my best,” Patty responded.

“I already have an assignment for you,” Madigan continued. “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 three weeks,” Madigan finished.

“I’ll get right on it, Mr. Madigan, and will have an update in three 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 was why the folks at NEMI didn’t emphasize these types of cost performance metrics in newer roadmaps.

Best Wishes,

Dr. Ron

Patty and the Professor: Heading Off HIP

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Patty, Rob, and The Professor finished their tasks in Shenzen and were flying to Shanghai for their last set of challenges in electronics assembly. Then they would head back to the US, Rob and Patty being only a week away from their wedding day.

As usual Rob, conked out as soon as the plane lifted off. Surprisingly, The Professor also drifted off to sleep. Patty was too excited to sleep. Rob’s mother had given her and Rob their wedding presents early … an iPad for each. They decided to bring only one laptop and one iPad. Patty was a little nervous about using the iPad for presentations but it worked quite well. She was still surprised that the iPad did not have a USB port. The Professor also gave each of them an early wedding present, a Pickett slide rule for Rob and a K&E slide rule for her. She must be the only person in the world right now that was watching a movie on an iPad and solving a math problem with a slide rule!

True to form, The Professor was passionate about how learning to use a slide rule helped improve a person’s innate math ability. He showed Patty and Rob how to use them and gave them several assignments. Rob was better with his slide rule than Patty due to the amount of “one on one” time he had with The Professor. She had to admit that using the “slip stick” gave one more of a feel for calculations and it was consistent with one of The Professor’s adages: “Always know approximately what the answer to a calculation should be … it will help you to avoid errors.”

In addition to the iPad and slide rule, Patty was excited to be going to Shanghai at the time of the World Expo 2010. Our trio had scheduled some time at the expo into their busy schedule.

Their plan was for Rob and The Professor to work on some productivity issues and for Patty to take on some of the process materials related problems. The three of them again met with the site GM for ACME’s newly acquired plant in Shanghai, a Mr. Wong. Wong was relieved to find that they all spoke Mandarin, as his English was a little rough. When The Professor addressed him in excellent Shanghainese, everyone was speechless. Patty was determined to ask him about this later. No American spoke Mandarin, Cantonese, and Shanghainese!

They again agreed to stick to Mandarin. Patty headed out to the line, accompanied by a young Chinese engineer, Zhou Chang, who seemed to be taking more interest in her than expected. She tried to make her engagement ring visible, but she wasn’t sure he recognized its significance. When she got to the line that was experiencing yield problems, she was met by the engineering manager, Fei Ding. He showed her some of the fails and she quickly identified head-in-pillow defect as the likely culprit. After investigating more fails, looking at stencil printing, some of the BGA components, and component placement, she asked Zhou Chang what spec was used to thermal profile the line.

“I don’t understand what you mean,” Zhou said in Mandarin.

“How do you determine what the reflow profile should be?” Patty responded.

With more discussion, Patty determined that they had one profile for all products! Fortunately most of the products were of similar, small thermal mass.

“What solder paste do you use for this line?” Patty asked.

The embarrassed silence suggested that Zhou did not know. They grabbed a tube and Patty was relieved to see that it was one of her favor solder pastes. Since profiling was so rarely performed, Patty and Zhou had to go to another part of the complex almost a mile away to find a reflow profiling unit. After taking the profile, the likely solution appeared. The 11-zone oven was very long and the reflow profile had a long thermal “soak” before the temperature went above liquidus. This long soak probably exhausted the flux, so that when the PWB went above liquidus, there was little flux left, resulting in oxidation and poor reflow.

All during their time together, she had mentioned that her fiancée Rob was with her on the trip. This information seemed to do the trick.

“Zhou, why don’t you look up the solder paste spec on the web and then set up the right type reflow profile,” Patty suggested.

It was clear that Zhou was troubled. It became obvious Zhou did not know how to profile a reflow oven. Patty set about working with Zhou to accomplish this mission. Within an hour they had re-profiled the oven and, over the next two hours, 300 PCBs were manufactured with the yield improved to 95%.

Patty asked Fei if she could give a brief presentation on the head-in-pillow defect to his team and he cheerfully agreed.

Her major points were:

HIP is caused by the failure of the BGA sphere to reflow with the solder paste. There are three major reasons for HIP:

1. Supplier Issues
a. Solder BGA sphere oxidation
b. Silver segregation to the BGA sphere surface

2. Process Issues
a. Stencil
i. Registration accuracy
ii. Insufficient solder paste
b. Component Placement
i. Off pad
ii. Out of plane
iii. Non optimum pressure
c. Reflow
i. Inappropriate reflow profile
ii. Flux exhaustion
iii. PWB warpage

3. Material Issues
a. Poor solder paste transfer efficiency
b. Insufficient solder flux oxidation barrier
c. Solder paste slump
d. PWB or BGA warpage

Patty went on to say that she had investigated all these issues with Zhou, and that the reflow profile was not optimum as the very long soak time had exhausted the flux. The other possible issues in the list did not seem to be a concern.

At the end of the day Patty, Rob, and The Professor met at the GM’s office to leave together for dinner and the Expo. Patty had to ask, “Professor, how can you possible know Mandarin, Cantonese, and Shanghainese?”

“Actually, I speak Min reasonably well, too,” he replied.

“How can this be?” Rob inquired.

“Mother and father were missionaries with Wycliffe Bible Translators,” The Professor answered. “I grew about around many languages during my youth. Mother and father speak more than I do.”

Patty went on to tell about the interest that Zhou Chang seemed to have in her, and how she had to discourage him.

“The burdens of being a beautiful young woman,” Rob teased.

Patty elbowed him, but they all left the taxi laughing as they headed for a restaurant near the Expo.

Best Wishes,

Dr. Ron

The Patty Chronicles: Leaning on Suppliers

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Patty was checking her email. She noticed a note from someone who had attended last night’s SMTA meeting. She had just been elected chapter president, after giving a talk on the head-in-pillow defect.

In her talk, she also shared how important it was to work closely with your materials and equipment suppliers. To her, it was obvious that her suppliers were interested in her success. If they were competent, why shouldn’t she rely on them for technical information and help? If she didn’t think they were competent, she should get new suppliers. She was surprised at how much “push back” she got from the attendees. Several stated that they felt that suppliers where just out to make a sale and that a smart person just bought from the supplier with the cheapest price.

Patty found this perspective negative and self-destructive. She was sure that 60% of all process knowledge was learned from her suppliers, either in person or at the technical conferences. She felt the main reason to go to these shows was the technical program. And some of the best papers were presented by the better equipment and materials suppliers. One of their marketing VPs even told her, “We believe that the more technical help we give our customers, the more successful we will be.”

Well, wasn’t that a condensation of what good business should be like? He who helps his customer is the most successful, she thought.

As she was thinking these thoughts a new email popped up on her PC. It was from Hal Lindsay, a noted curmudgeon. Patty read on.

“I heard you telling some of the people at the meeting last night that lead-free assembly had some process advantages. Hogwash. Lead-free has no process advantages, and it’s not needed,” he started.

After a few more complaints, he finished, “It’s because of young tree-huggers like you that never stood up and fought lead-free that we are in this mess to begin with.”

In preparing her response, Patty’s mind went back to some conversations about this she had had with The Professor. He had made two strong points:

1. The first purpose of RoHS is to make recycling safer. So much recycling unsafe processes is performed in poor countries with unsafe practices. RoHS-compliant products will save the lives of the unfortunate people who have to perform this type of recycling to survive.

2.  Lead-free soldering is challenging because the solder does not wet as well. This situation forced us to develop assembly processes with tighter process windows. However, an initially unseen benefit is that tighter lead spacings are possible with lead-free soldering because of this poor wetting. Many portable products such as mobile phones could not be assembled with leaded solder. There would be too many shorts.

Patty was including this information in her response to grumpy Mr. Lindsay, when the phone rang. It was Rob.

He began, “?????????????ACME???????????????????????????”

(For our few readers that can’t read Mandarin: “It looks like I will be traveling to China to visit some of ACME’s new factories there. I think you will be going to work on some soldering issues too.”)

“Whoa!,” Patty exclaimed, “Why would you be going to visit ACME’s factories in China?”

Rob went on, “You know things haven’t been going well here at AJAX, we never adopted “Lean Sigma” techniques like ACME did. Today, we had a layoff and I got hit.”

“Yikes!” screamed Patty. Her mind went through many scenarios with Rob being unemployed five weeks before their wedding.

“Easy,” Rob implored. “My GM called me in and said that he was sorry to see me go, but being a friend with your GM, he got me a job at ACME. I am to be the liaison for the three factories that ACME has in China. My fleuncy in Mandarin made the difference,” he finished.

Patty and Rob were unusual for Americans in that they both spoke Spanish and Mandarin. Both had fathers who encouraged them to take Mandarin at Tech as they had both taken many years of Spanish in high school. Both did a language study abroad (LSA) term and an internship in China. As their dads said, “If you can speak English, Spanish, and Mandarin, you can speak to almost any professional in the world.” Both Patty and Rob found that their language skills gave them a ready bond when they were abroad. One German colleague even told Patty that she was the only American he knew that would not fit the European view of Americans when they ask, “Are you bilingual, trilingual or American?”

After Patty calmed down, she asked Rob why he thought she would be going.

He responded, “When your GM gave me the job offer on the phone, he alluded to a team visit to China, by me and this genius young woman that is a process expert. Apparently, they have some head-in-pillow, graping and productivity issues. I will be handling the business aspects, you the technical. He also mentioned he would like The Professor to go. I don’t think he knows we are engaged.”

Patty congratulated Rob and finished to conversation. She hoped that their being married wouldn’t create any issues in working together. She also was a little annoyed that she always seemed to be the last to know about trips that the executives were planning for her and her team. It was especially annoying that Pete seemed always know before her when they would need to go on one of their adventures. After all, she was Pete’s boss. Well, at least this time it was Rob, not Pete. There is now way Pete could know about this potential adventure.

She went back to finishing her note to cranky Hal Lindsay when she heard, “Pack your bags kiddo, it looks like China this time. Oh, and Rob is going.”

Cheers,
Dr. Ron

I saw Patty at a recent SMTA meeting.  I mentioned that many of her fans would like to see a photo of her.  Surprisingly, neither of us had a camera.  As you remember she is also a self taught artist,  I asked if she would mind sketching herself.   Here tis.

The reflow image of leaded and lead-free solder coutesy of Motorola.

All the best,

Dr. Ron