Category Archives: Dr. Ron

Materials expert Dr. Ron Lasky is a professor of engineering and senior lecturer at Dartmouth, and senior technologist at Indium Corp. He has a Ph.D. in materials science from Cornell University, and is a prolific author and lecturer, having published more than 40 papers. He received the SMTA Founders Award in 2003.

Density Calculation Still Raises Questions

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Folks,

It is hard to believe, but I have been blogging now for over 8 years. In all of that time, the most popular topic by far has been the calculation of alloy densities. Many people are troubled by the required equation. At first blush it doesn’t seem logical. I have derived it, but here is an effort to try and make it more intuitive.

A reader wrote the following, which inspired my explanation that follows.

Craig writes:

Why do we calculate the theoretical density of an alloy by using the formula of:
1/Da = x/D1 + y/D2 (binary) or
1/Da = x/D1 + y/D2 + z/D3 (ternary) as opposed to multiplying the individual metals’ densities by their percentages in the alloy and adding them together ? I thought the density of an alloy would be analogous to a weighted average of the densities of the metals in the alloy. Obviously, that is wrong, but I don’t understand why?

The reason you have to use the non-obvious formula is that density is given as mass/volume. So there are two quantities to be concerned with, and one is inverse (i.e. volume is 1/volume in the density formula). So you have to use the equations above, or you will be in error. I derived these equations in a previous post. However, many people do not find the result intuitive.

Here is, hopefully, a more intuitive example. Let’s say, for some strange reason, you were interested in inverse height. So let’s say John is 5 feet at his shoulders, or 1/5 inverse feet. His girlfriend Kathy is 5 feet tall, also 1/5 inverse feet. Kathy stands on John’s shoulders. How many inverse feet is their total height? The tendency would be to say they are 1/5 +1/5 = 2/5 inverse feet. But we know that when Kathy stands on John’s shoulders they span 10 feet, so they must be 1/10 inverse feet. So, to calculate their height in inverse feet, we need to use:

1/IFT = 1/John IF + 1/Kathy IF = 1/(1/5) +1/(1/5) = 10

IFT = 1/10

Note: (IFT = Inverse Feet Total)

The same is true for density, since density = mass/volume (inverse volume is like inverse feet).

Another engineering example is electrical resistivity and conductivity. If the resistance of one wire is 2 ohms, and another is 1 ohm, and we connect them in series, the total resistance is 3 ohms. However, if we consider conductivity, one wire has a conductivity of 0.5 mho and the other 1 mho. Again, to get the total conductivity we don’t add the conductivities, we must use:

1/Ctotal = 1/C1+1/C2 = 1/0.5 + 1/1 = 2+1 = 3. So Ctotal = 1/3 mho.

I hope this helps.

Cheers,

Dr. Ron

 

IPC Tin Whisker Conference Sheds New Light

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Folks,

I just returned from SMTA/INEMI’s Medical Conference in Milpitas (near San Jose/San Fransisco), where I spoke on tin whiskers. I then quickly traveled to Costa Mesa (400 miles south, near Los Angeles), to IPC’s Tin Whiskers/Reliability Conference, where I spoke on Weibull Analysis. Both shows where attended by 80-plus people.

Most noteworthy, at the IPC Tin Whiskers Meeting, was Raytheon’s Dave Pinsky’s presentation, titled: “Tin Whiskers at a Large Defense OEM: Past. Present, Future.” In addition to discussing claims that some vendors have of producing whiskerless tin coatings and other topics, most helpful was his mention of a report by the Government Electronics and Information Technology Association (GEIA) on Tin Whisker Risk Mitigation. This standard, GEiA-STD-0005-2 discusses mitigation details thoroughly. Not only has the knowledge of tin whiskers increased, there appears to be more confidence in coatings for mitigation. However, in mission-critical applications, a well thought out, multiple mitigation approach to tin whiskers is still needed. The image below, taken by NASA, shows a tin whisker next to a human hair. Tin whiskers are very thin indeed!

Cheers,

 

Dr. Ron

Is the PC Dead?

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Folks,

Let’s see how Patty is recovering from her conflict with Hal Lindsay.

Patty saw a link on one of the daily industry newsletters that piqued her interest. It was titled, “A New Alloy for Medical Electronics Applications.”

The paper talked about a new SAC (tin-silver-copper) lead-free solder alloy that contains a small amount of manganese. Apparently, the manganese modifies the metallurgical structure and enables the alloy to perform well in both drop shock and thermal cycle tests.

She finished the article and decided that she needed to look into this alloy more. It isn’t common for an alloy to perform well in both drop shock and thermal cycle. The title also reminded Patty how relieved she was that their St. Paul facility was getting ready for Medical RoHS on July 22, 2014.

She then checked her email and saw she had a note from ACME CEO Mike Madigan.

Coleman,

I just read an article about the death of the PC. PC sales are off by 10% per year. That means in 10 years they will be gone. PCs are 30% of our business. Develop a plan to modify our business so that we can replace this loss. Be ready in two weeks.

Madigan

Patty had to chuckle at Mike Madigan. He seemed to totally lack social skills. She wondered how someone could get so far in the company without them. Anyway, she had a new assignment. Also, she quickly determined that a business decreasing 10% per year would still be at about 35% (0.9^10= 0.349) of its original size in 10 years.

Right off the bat, her sense was that the “Death of the PC” was exaggerated and misunderstood. She performed a search and read some more articles, finding several that talked about the surge of tablets like the iPad and the Kindle Fire as being behind the PC’s decline. She and Rob owned two iPads and one Kindle Fire. Were they part of the trend? She suspected that there was more to the story and thought that discussing this topic with The Professor would be interesting. She was visiting him at Ivy University later in the week.

The week went by quickly and, before Patty knew it, she was in her car with her husband Rob, driving the two hours from Exeter, NH, to Ivy U. Rob was getting his Ph.D. there, part-time, and made the trip several times a month. The Professor was his advisor.

Rob needed an hour with The Professor. During that time, Patty checked her email. After he and Rob were finished, The Professor said, “Let’s go the lunch at Simon Pearce and chat about your latest adventures.”

“That’s great! Simon Pearce is my favorite restaurant, Professor,” Patty responded. Simon Pearce Restaurant in Quechee, VT.

They both looked at Rob, but he had so much work to do that a slice of pizza from the student union was his destiny for lunch today.

As Patty and the Professor arrived, Simon Pearce was at its most beautiful. The sky was blue and the leaves were just starting to turn. Patty had alerted The Professor that she wanted to talk about the “Death of the PC,” so he was ready as they sat down.

“Patty, I have read all of the articles that you sent. They emphasize the impact on the PC by tablets and mobile phones, but they miss an important point,” The Professor began.

“What’s that?” Patty asked. “The effect of the constancy of ‘Memory Metrics,’” The Professor replied.

“What are ‘Memory Metrics?’” Patty asked.

“Let me explain with a story,” The Professor answered.

“When you were a toddler, back in 1986, my family got our first computer, an IBM PC XT. It cost $6,000 and had 0.512MB of RAM and 20MB on the hard drive. We had it for 3 years and needed a replacement. Can you guess why? The Professor asked. The IBM PC XT circa 1986.

“You ran out of memory,” Patty answered.

“Yes, the Kids where playing, ‘Where in the World is Carmen Sandiego,’ and some other games,” The Professor said.

“Then we had to get another computer in 1989 with 4 MB of RAM and a 200MB hard drive. We tripled the hard drive memory and still needed a new computer in 1995. This trend continued until about 5 years ago, but it then slowed down,” The Professor continued.

“Why did the trend slow down?” Patty asked.

“Before I answer that, we need to discuss ‘Memory Metrics,’” The Professor said. “How much memory does a decent photo require?”

“About 1MB,” Patty answered.

“A song?” The Professor quickly shot back.

“About 5MB,” was Patty’s fast reply.

The banter continued.

“A book?”

“About 1MB.”

“A full length movie?”

“About 5,000MB.”

The Professor was impressed.

“Wow, Patty! It’s amazing that you know all of the critical ‘Memory Metrics.’ Where did you learn them?” The Professor said.

“Rob went to lunch with the professor who teaches a class called Everyday Technology. They discussed these metrics. It helps me to estimate how much memory I need on my smartphone to store all of my photos, songs, and books,” Patty answered.

“So how many songs could you store on the hard drive of my first computer?” The Professor asked.

“Only 4 or only 20 photos or books,” Patty answered.

“So, we weren’t putting songs, books or photos on early computers. Even the $10,000 laptop that I needed for my research in 1996 only had a 1000 MB hard drive … only 200 songs,” said The Professor.

“I get it,” Patty responded, “Let me see if I can fill in the blanks.”

“Memory Metrics, are close to constant, with the exception of perhaps photos with more megapixels. Anyway, the memories on new computers have gotten so large that we don’t need to replace them as often, we just don’t fill the memories up any more. Unless we store movies,” Patty continued.

“Add in the advent of smartphones and tablets and see if you can make an argument for why PC sales are down,” The Professor said, beaming at his favorite student.

“Well, before smartphones and tablets you might get a new PC even if you didn’t need it. But, now you have two or three devices to buy, so you may put off a new PC for awhile to buy a new smartphone or tablet,” Patty responded.

“So, what will happen to smartphones and tablets?” The Professor asked.

“A similar thing. They are developing so many features, memory, and computing power, that their sales will slow done in a few years,” Patty thoughtfully said.

“So, the PC is not dying!” Patty exclaimed.

“But, what about the tablet forcing out the PC as a replacement?” Patty asked.

“Let’s ask my statistics class after lunch,” The Professor suggested.

Although Patty had been around campus off and on, she was immediately struck by how young everyone in the class looked. Just last night, Rob was teasing her about her first gray hair. That, no doubt, added to this effect. As the class of 60 students settled down, The Professor began to speak.

“Before we start the lecture, my colleague, Patty Coleman, would like to ask you a few questions,” The Professor said.

“The Professor calls me a colleague! Wow!” Patty thought.

So, Patty stood up and started speaking. “If you could only have one device, a PC or a tablet, who would choose the PC? “ Patty asked.

Everyone raised their hand.

“Why?” Patty asked.

A boy, who looked, to her, to be about 12 years old, answered, “Well, Dr. Coleman, it is very difficult to write a 10-page paper on a tablet, or perform Excel calculations, or prepare a PowerPoint file on a tablet.”

“How many of you own a tablet?” Patty asked.

Only about 20% of the students raised their hands.

“How about a smartphone?”

Everyone raised their hands.

“Any thoughts on why many people think the PC is dead and the tablet is the future?” Patty asked.

After a little murmuring a female student raised her hand. Patty was relieved that she looked to be about seventeen. Patty acknowledged her.

“Well, Professor Coleman, my family has two tablets at home. My 7- and 9-year old brother and sister play games on them all the time. My mom and dad use one as an e-reader, and they use one to control our TV. But, for any serious work, even they prefer a PC. Only my kid brother and sister would prefer a tablet over a PC. But, the most recent devices we bought were tablets. Our PCs just haven’t needed replacing,” the young women said.

“Why do so few of you have tablets at school?” Patty asked the group.

Again more murmuring ensued and, finally, a graduate student raised his hand. Patty acknowledged him.

“Professor Coleman, I find that the combination of a PC and a smartphone fills all of my needs. I can listen to music or read a book on my smartphone. I can’t not have a smartphone and function at today’s university. A tablet would be a luxury, I don’t feel I need or can afford,” he said.

With that Patty sat down. This information on tablets and the college scene was consistent with what Patty had read. The Professor’s lecture was on Bayes Theorem and Patty decided to stay. She chuckled that the students thought she had a Ph.D. and was a professor. “Yikes, does this mean they think I am old?” she thought.

After the lecture Patty thanked The Professor and went to find Rob. She now felt she understood why PC sales were down. Tablets had some effect, but the near stability of Memory Metrics and the tremendous computing power and increased memory of a modern PC simply meant people didn’t need to upgrade as often. She expected similar trends for smartphones and tablets. As she organized her backpack, she put her 6 month old laptop, with its 16,000MB of RAM and 1,000,000MB hard drive away.

The PC was alive and well.

Best wishes,

Dr. Ron

Patty and the Professor: What Homogeneous Means

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Folks,

Let’s see how Patty and Pete are doing with their Medical Device RoHS Crisis ….

Patty and Pete sat in a plane on the runway of the Manchester, NH, airport. Patty was just calming down after Jeff Sparkel  told her that Hal Lindsay had performed an analysis to show that the flagship medical device that Jeff’s factory assembled was RoHS-compliant using tin-lead solder. Corporate RoHS compliance was under her responsibility and she was panicking that ACME’s St. Paul site would miss the July 22, 2014 compliance date for medical devices. She literally drove straight to the airport after chatting with Sparkel on the phone. Fortunately, she and Pete both had a three-day suitcase in their offices for such emergencies. Rob’s mom agreed to help with her twin boys. What a blessing to have a mother-in-law like Rob’s mom.

To add to the stress, she and Pete almost missed the plane. He insisted that he needed to stop at a drug store, though he was secretive about the reason.

As the plane lifted off, Patty had to find out about this drug store mystery.

“OK, Pete. Why the drug store?” Patty asked.

“I’m afraid that, if I tell you, you’ll lecture me,” Pete said sheepishly.

“Out with it! Out with it,” Patty commanded.

“I bought Vick’s VapoRub to put under my nose when we are with Mr. Lindsay.  Ain’t no way I’m gonna’ be with that stink bomb unprepared,”  Pete responded.

Patty was going to say something but she started chuckling uncontrollably.

“You are welcome to share with me,” Pete offered.

As Patty tried to catch her breath, she just shook her head no.

They arrived at their hotel room at 10PM, after a quick, late dinner.

Fortunately, the timing of events was favorable. Lindsay had planned to give his final presentation the next day. Sparkel was actually pleased that Patty asked to attend.

Patty met Pete for breakfast at 7AM. By then she had run 5 miles, worked out with weights at the hotel gym, and showered. They arrived at Sparkel’s office at 7:45 and headed directly to the conference room where Lindsay was preparing to present. Upon seeing Patty and Pete, Hal Lindsay seemed surprised and turned a little red in the face.  Pete checked the room for ventilation.

Patty and Pete agreed to listen to Lindsay’s complete presentation without interruption.

“I know everyone here except for that guy in the back. He looks like a lawyer,” Pete whispered into Patty’s ear.

“He looks like a lawyer because he is one,” Patty responded. “He is my special guest,” she said.

Lindsay began his presentation sharply at 8AM. Patty had to admit that she was impressed with Lindsay’s experimental procedure. He had taken three of ACME’s St. Paul site’s highest-volume products and carefully performed teardown analyses. He painstakingly extracted all of the solder from the PCBs. One product weighed 10.2 kg and contained 11.2 grams of tin-lead eutectic solder. Patty checked Lindsay’s calculations. The fraction of lead in the unit was 0.042%, less than 0.1% that RoHS requires. All three products were below 0.05% by weight lead.

Lindsay then discussed his plan to analyze enough units to give the data statistical confidence. His charge would be an additional $20,000. Jeff Sparkel then asked if there were questions.

Patty raised her hand.

“Mr. Lindsay, what about RoHS’s requirement that all concentrations of substances of concern by ‘per homogeneous material?’ ” Patty asked.

Lindsay looked confused. His face turned a little red. It appeared that he didn’t understand what she was asking.

“Patty, please explain what ‘per homogeneous material’ means?” Sparkel asked.

“It means that any part of the product that could be mechanically separated must be less than 0.1% lead. As an example, a soldered joint can be cut out of a medical device with an X-Acto knife. Accordingly, the small piece of solder must be RoHS-compliant, so the solder itself must have less than 0.1% lead,” Patty explained.

“Per hemorrhoidgenous material, don’t apply to no medical devices,” Lindsay grumbled.

Both Patty and Pete had trouble not chuckling at Lindsay’s mispronunciation of “homogenous.”

“I beg to differ. Dr. Coleman’s explanation of ‘per homogenous material’ is spot on,” said Patty’s special guest.

Patty chuckled to herself when she realized that her guest thought she had a Ph.D.

“Who are you?” asked Jeff Sparkel.

“I’m Aaron Toynbee, Esq, our company’s general counsel. My department has responsibility for interpreting corporate compliance with environmental laws like RoHS.  We have studied the RoHS law extensively and the requirement for medical device compliance. Almost all of the medical devices we manufacture must meet RoHS compliance by July 22, 2014. I was alarmed when Dr. Coleman pointed out that there was some lack of understanding here about this.” Toynbee said.

After Toynbee spoke, it was agreed that the St. Paul team would work with Patty and Pete to resurrect the RoHS initiative that had been developed some time ago. Patty let out a deep sigh of relief.

Just as it appeared that the meeting was over, one of the younger engineers asked, “Are we still going to have Mr. Lindsay perform the analysis he suggested. It seems to me that there may be some benefit in getting this type of data.”

There appeared to be some murmuring of agreement. Hal Lindsay brightened, as it appeared that his proposed work might still be accepted.

Patty sat by watching this with incredulity. She remembered the Professor telling her that sometimes people will be too polite and not say what needs to be said. This was not going to be one of those times.

“You have got to be kidding me!” she shouted.  “There is no way we are going to continue any of this useless work!” she said even louder.

At this, Hal Lindsay’s  face turned beet red and he charged over to where Patty and Pete were. Out of the corner of her eye, Patty could see the Vick’s VapoRub gleaming under Pete’s nose.

Patty was now standing up and Lindsay had advanced to within five feet of her.

All of the sudden Lindsay came up to within a foot of Patty.

“It’s tree-huggers like you that that allowed this RoHS crap to happen in the first place,” he screamed into her face.

Patty was not prepared for this olfactory assault. Worse yet, some of Lindsay’s spittle ended up on her face. A natural gag reflex took over and she started having trouble breathing. Those in the meeting were horrified as they watched Patty crumble and slump to the floor.

Pete jumped up and instinctively and firmly pushed Lindsay back away from Patty. His Vick’s VapoRub doing its job. Sparkel’s  second-in-command, Jennifer Halliday, gently escorted Lindsay from the building, before any fisticuffs ensued.

Sparkel  and one of the female engineers helped Patty as she tried to get up. Within a few moments Patty was herself again. Everyone knew what happened, but when Patty said she probably should have eaten more for breakfast, everyone murmured in agreement.  Sparkel asked if just he, Patty, and Pete could wrap things up. Patty agreed, but asked to go to the ladies room first.

When she returned, Patty again reiterated that medical devices have to obey the “per homogeneous material” requirement and that the only way this was possible was to change to a lead-free solder. Patty and Pete confirmed their agreement to stay on for a few days to work with Sparkel’s team, to resurrect the plan to be RoHS-compliant by June 2014, a month early.

With two days of hard work, the plan was redeveloped, and Patty and Pete were confident the St. Paul team was on the right track. Jeff Sparkel apologized to Patty about 10 times.

Within no time Patty and Pete were back on the plane, heading home.

“Hey kiddo! You should receive hazardous duty pay for this one,” Pete teased.

“No kidding,” Patty responded.

“When you said you needed to go to the ladies room, I was a little worried,”  Pete said. “I thought maybe some permanent damage was done,” he went on.

“It was worse than that. I had to wash Lindsay’s spit off my face,” Patty groaned.

“Definitely Purple Heart material,”  Pete teased.

They both chuckled.

 

Cheers,

Dr. Ron

 

‘Per Homogeneous Material’ Also Applies to Medical Devices Under RoHS

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Folks,

It’s been awhile, let’s see what Patty is up to….

Patty was in her office, finishing lunch and reading Golf Digest. She was happy to see Tiger Woods doing better, but a little disappointed he didn’t do well in the PGA Championship. Like others, she was touched to see him holding his young son after a recent tournament.

Lost in thought, she was startled as Pete knocked on her door.

“Hey kiddo! Did you hear the latest?” Pete teased.

“OK. Go ahead and tell me. You always have the scoop,” Patty replied with a friendly chuckle. By now Patty was used to the fact that Pete always seemed to know what was going on before she did.

“Our plant in St. Paul, the one that assembles medical devices, is not going to have to convert to lead-free solder. So, nobody there is working on the transition,” Pete replied.

“They are too! As you remember, we had a lead-free and RoHS kick off meeting there in March. You were with me,” Patty shot back, a little annoyed.

“’Tis true. ‘Tis true. But, that was before Hal Lindsay hit the scene,” Pete said.

“How is that blowhard involved? Patty asked, her face turning red. Lindsay was an anti-RoHS curmudgeon who used to attend Boston area SMTA meetings. He and Patty had several heated discussions about RoHS while at these meetings. Lindsay was a physically big, intimidating man, and one of their encounters left Patty shaken. She remembered him screaming at her, “Its tree-huggers like you that allowed lead-free laws to get passed in the first place.”

“Well, the GM of the St. Paul plant has been convinced by ‘Halitosis Hal’ that they don’t need to do anything to comply with RoHS,” Pete continued.

Patty repeatedly warned Pete about using derogatory nicknames, but she forgot herself and chuckled a little bit. At one SMTA meeting, Hal’s breath was so bad that he stunk up the corner of the room in which he was sitting.

Patty composed herself, “Jeff Sparkel, is a great GM. How did Lindsay convince him it was possible to comply with RoHS and not switch to lead-free solder?” Patty asked.

“I think it has to do with ‘per homogeneous material,’” Pete replied. “I’ll have to talk to Jeff and see what is going on,” Patty stated. “Better do it soon,” Pete suggested, “Medical equipment RoHS compliance is less than a year away.”

As Pete left her office, she admonished him, “No more calling him “Halitosis Hal’,” but then she cracked up herself.

Jeff Sparkel was one of Patty’s favorite people. He was warm, engaging, hardworking, and reasonable to work with. However, he was more a businessman than an engineer. He had his MBA from Ivy University and knew The Professor.

Patty reached for her phone to give him a call. He picked up on the first ring.

“Hey Patty! What’s up? it’s great to hear from you,” Jeff said. Patty explained why she was calling, and the fact that she was alarmed at what Pete told her.

“That Lindsay is a piece of work, I’ll grant you that. But, he told us he can prove that we don’t need to go lead-free for only $10K. So we hired him,” Jeff said.

“What did you get for that?” Patty asked.

“He carefully took apart one of our medical office units that was scrapped. He extracted all of the solder and weighed it. He showed us that the weight of the solder was less than 0.05% of the weight of the unit. RoHS requires less than 0.1%, so we are golden. He wrote a report. Best $10K I ever spent. It was going to cost us more than $300K to convert to lead-free,” Sparkel summed up.

Patty had the worst sinking felling she had since she joined ACME Corp. Jeff’s business had to be RoHS compliant by July 22, 2014, and he had lost almost 6 months of prep time.

“Jeff, Yikes! Apparently no one on your team understands RoHS’s ‘per homogeneous material’ requirement” Patty exclaimed.

The was only silence on the other end of the phone.

What is, “per homogeneous material?” Is it important? Will Patty and Pete confront Hal Lindsay?

Stay tuned.

Cheers,

Dr. Ron

First-Pass Yield, Continued

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Folks,

Let’s see how Patty is doing with her latest challenge …

Patty had decided to call The Professor and see what advice he had to offer in preparation for her visit to the facility in Sherbrooke, Quebec  that the senior management  of her company wanted to buy. She was having trouble understanding how it was possible to have 99.5% yield, great uptime, and balanced lines and still have poor profitability.  After a short discussion, The Professor seemed like he was ready to sum the situation up.

“Patty, I think you will find that the poor profitability is the result of high rework costs,” he said.

“But, Professor, how can that be when the first-pass yield is 99.5%? There is almost nothing to rework,” Patty replied.

The Professor chuckled, “Keep an open mind,” he advised.

Then he continued, “Don’t worry, you will figure it out in a heartbeat”.

Patty wished she could be so confident. As she was about to say good-bye, she mentioned to him her observations of so many teens being glued to their smartphones during her recent Williamsburg vacation. She also shared her concern for her two sons growing up in this over connected world.

“Patty, the main thing your sons have going for them is that they have you and Rob as parents. You will help steer them in the right direction, I’m sure. Remember to lighten up a little, after all they are only 5 years old,” The Professor chuckled.

As he was about to say good-bye, he thought of something else to share with Patty.

“Say Patty, you remember that, here at Ivy University, we have information sessions with high school students that are interesting in coming to our engineering school, right?” he asked.

Patty thought for a moment and remembered how impressive that was. It was the only university she knew of in which professors would meet with high school students and their families to discuss the benefits of an Ivy University engineering education.

“Sure, Professor, it’s a great thing Ivy U does,” Patty answered.

“Because of this program I have spoken to hundreds of high school students, I have also given presentations to high school students in larger groups. Give me a few moments with a high school student and I can tell if they are Ivy U material,” The Professor stated.

“How is that possible?” Patty asked.

“I look for two signs. The first is if their parents are much more interested than they are, that is a bad sign. The other is that if a high school student finds someone like me interesting, that’s a good sign,” The Professor chuckled and then continued.

“I know, to the typical 17 year old, I will seem like a boring nerd, however, to someone passionate about learning, I will likely be seen as a fecund resource, even if they are only 17,” he finished.

Patty chuckled a little herself, thinking that only The Professor, would use the term “fecund resource.”

Patty said farewell to her mentor and called Pete to make arrangements to leave for the Manchester, NH, airport, about an hour from their office in Exeter.

By the end of the day they were at their hotel in Sherbrooke. They had dinner at a French restaurant and both agreed to try and speak only French. Each of them slipped in a little Spanish inadvertently, a common problem among those who speak several Romance languages.

After a good night’s sleep, they met for breakfast. At breakfast they agreed on a few things:

  1. They would try and speak French at the meeting.
  2. They would discuss using preforms to solve the QFN voiding problem first as they expected this topic to be more controversial.
  3. The profitability problem, they would leave for last as they anticipated that this would take time, but were expecting less controversy.

After a short drive from the hotel, they were at the facility. Pete commented on the logical way that exits were numbered on Canadian highways, by the number of kilometers from a reference point.

As they approached the receptionist, Pete proclaimed, “Bonjour, comment ca va? Nous sommes là pour répondre à Jacques? (Hello, how are you? We are here to meet with Jacques.)

In a short time, Jacques appeared.

“Bonjour Jacques, mon nom est Patty et c’est Pete. Nous aimerions parler en français si c’est acceptable.” Patty cheerfully said. (Hello Jacques, my name is Patty and this is Pete.  We would like to speak in French if that is OK.)

“Ah, my friends, French probably won’t work for us. You speak with a Parisian accent, suggesting you learned European French. Our French has many different words, we almost always speak in English with our customers and partners from France,” Jacques responded.

Patty thought a minute and it made sense. Quebec has been separated from France for 250 years, but then it occurred to her that the US and Great Britain were separated for about the same amount of time. Maybe this is why some people say that the US and Britain are two cultures separated by a common language, she thought.

They went to a conference room and began discussing the QFN voiding issue.  Jacques presented his data and Patty and Pete gave a presentation on how solder preforms can minimize QFN voiding. Patty gave Jacques a copy of Seth Homer’s paper on the topic.  Both Pete and Patty were surprised at how receptive Jacques was to using preforms.  It seemed that this trip may be easier than they thought.

“Jacques, is it OK if Pete and I walk around and observe the manufacturing process for a while,” Patty asked.

“Sure, take a couple of hours and then we can go to lunch,” Jacques responded.

So Patty and Pete headed off to see the 3 SMT and through-hole assembly lines.  Upon entering the facility, they were stunned to see what appeared to be scores of rework operators.  Patty went over to observe more closely.  It appeared that right after the PCBs were assembled they were visually inspected.  Many of the boards went directly to a rework station.  The boards that appeared to pass the visual inspection, went to an in-circuit testing.  Most of these boards, also went to rework stations. The so-called first-pass yield was obviosuly measured after all of this repair work.

“Pete why don’t you check out the rest of the processes, I’ll stay here and see if I can get a true first-pass yield count,” Patty suggested.

So Pete went off to observe the other parts of the SMT and though hole processes and Patty stayed and counted boards to determine first-pass yield.  After a little more than an hour, they met  in the break room to sum up the situation.

“Well, for the hour I was there, 150 boards were assembled on the one line I was watching. The first-pass yield was only 24%,” Patty groaned.

“I can top that!” Pete replied.  “They have a pencil pusher,” he chuckled.

Patty choked on her ice tea.  As she recovered, she was able to say, “Just like in Mexico?”

“Yep! Same scenario,” Pete responded.

Several years ago, Patty and Pete were at a shop in Mexico, and observed an operator pushing a component, on a board that had exited a component placement machine, with a pencil.  The component was out of alignment and the operator was straightening it.  No one knew how to program the placement machines to correct for this error.

“Any other interesting phenomena?” Patty asked.

“They use the same paste and print parameters, no matter what the stencil. It’s no wonder their first pass yields are low,” Pete finished.

As they summed things up, they were a little down, as they recalled past adventures when they had to deliver bad news.  Patty, then had an idea.

“Pete, why don’t we offer to have you come here for a week or two to help them?” Patty asked.

“Sounds like fun,” Pete replied.

“But we have to get them to agree that first pass yield is measured as the boards come off the assembly line.  Without this metric they can’t assess where their processes need improvement,” Patty added thoughtfully.

“And we need to plot the defects on a Pareto Chart to develop a continuous improvement plan,” Pete commented.

Figure 1. A typical SMT Board assembly Pareto chart.

“It is amazing that their line balancing and uptime are so good,” Pete added.

They were both apprehensive as they met with Jacques.  They remembered some of the times that folks became hostile when bad news was delivered.

Patty did the best she could to keep it positive. She started with their strengths (uptime and line balancing) and complimented them on how strong these important metrics were.  She then shared their “opportunities for improvement” and offered Pete’s help.

“My friends, thank you. What a gracious offer.  I accept,” Jacques said gratefully.  “I guess the workshops I attended on uptime and line balancing paid off. They were presented by this interesting chap everyone calls The Professor,” he finished.

Patty and Pete were stunned by how well this trip went. They enjoyed a delicious French lunch at a café near the plant, with Jacques. On the trip home they chatted about how important it is to the measure first-pass yield before any rework is done, and to plot the defects in a Pareto Chart to lay the foundation for improving yields. Patty now understood what The Professor meant when he said, “look at the rework costs,” they were reworking before they measure their yields.

Epilogue:  Two months later true first pass yield was at 94%.  Costs plummeted with less rework and business soared. As a result of the increased business, full employment was maintained. Patty’s company did end up purchasing this facility. In addition, Patty and Pete became fast friends with Jacques.

Cheers,

Dr. Ron

Note:  As always, this story is based on a true incident.

 

Patty and the Professor: Filling the Void

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Folks,

Let’s see what is up with Patty….

Patty sat at her computer, admittedly a little tired. She had just gotten back after a week’s vacation in Colonial Williamsburg with Rob and their two sons. Even though the boys were only five years old, she had insisted that they go to the historical triangle and get the two young lads started on American history. She and Rob had been speaking Mandarin and Spanish at home and the boys were both trilingual, so visiting Williamsburg was among other things Patty had planned to prepare them for a rewarding and productive life.

OK, maybe she was an overachiever for her sons, but she remembered the profound impact that visiting this historic treasure had on her when she was a young girl. During this visit, the young family alternated days at Colonial Williamsburg, Busch Gardens and Water Country USA. They also ate dinner at two of the historic eateries. Of course, at their young age, her boys enjoyed Busch Gardens and Water Country the most.

She had to admit that the trip left her a little shaken. She saw scores of youngsters mesmerized with their smartphones or tablets while standing in line for a ride at Busch Gardens. More troubling was watching teens texting in Colonial Williamsburg while a character interpreter explained the making of a flintlock rifle or the impact of the Royal Marines taking the gunpowder from the Williamsburg magazine, early in the Revolutionary War.

Patty clearly recognized the profound benefit of electronics, after all, it was her career! However, she was troubled by its overuse, replacing personal human interaction and intellectual pursuits and its luring many children away from playing. She was stunned to go to the park where she grew up, a few weeks ago, and finding no children on the swing sets, slides or monkey bars.

More troubling, was a recent chat she had with the Professor. He told her he was convinced that the likelihood of a high school student getting into an elite university was inversely proportional to the number of text messages they send each day. He pointed out that according to Sherry Turkle in her seminal book, Alone Together, the typical US teen sends 200 texts a day. He went on to explain that if a teen sends that many texts a day, how can they have time to be studying Milton or the rise and fall of Rome, learning calculus, or becoming proficient in any topic needed to get into a competitive college or university? To make the point that better students don’t send many texts a day, The Professor even surveyed his statistics class at Ivy University and found that on average the students there sent only about 20 texts a day.

With all of these conflicting thoughts swirling in her mind, she was startled by Pete coming to the door.

“Nous allons à Québec!” Pete shouted. Patty had to shake her head a little bit to get the cobwebs out.

“Hey kiddo, you look a little tired. Too much vacation?” Pete teased.

“Yeah, we didn’t get home ’til 11:30 pm last night. Anyway, what’s up?” Patty responded.

“Well, while you were away, our beloved senior management decided they might want to buy a company in Quebec, near Sherbrooke,” Pete answered.

“Why will we be going to Quebec if we haven’t bought the company yet?” Patty asked.

“The company has 99.5% first-pass yield, but their financials are not that great, especially return on assets,” Pete replied.

“Looks like maybe their uptime or line balancing may be bad,” Patty commented.

“Their throughput would suggest otherwise, for the three lines they have,” Pete said.

“Hmmm, interesting,” Patty murmured.

“Oh, one more thing. They probably need to be using solder preforms on QFNs in some smartphones. They have a voiding warranty issue.” Pete added.

How can a company have outstanding yield and good throughput and still not be profitable? What about solder preforms? Stay tuned to find out.

Cheers,

Dr. Ron

The Limits of Mixing: A Chocolate Chip Example

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Folks,

We tend to think of mixing as something that can completely even out those things being mixed. As an example, let’s assume you are making chocolate chip cookies and would like to have 10 chocolate chips in each large cookie. You make enough batter for 100 cookies and then mix in 1,000 chocolate chips. After mixing for a long time you put 100 dollops of the batter on the baking pan and bake up the cookies. Upon inspecting the cookies, to your dismay, you find that you have only 13 cookies with 10 chocolate chips. More than 40 cookies have 30 percent more or 30 percent less than 10 chips. Worse yet, 3 cookies have 4 or less chocolate chips and 7 have 16 or more. See the graph below. You decide that you did not mix them enough, so you make another batch and mix for 4 hours.  The results are the same.

Statistics tells us why the above scenario is so.  In a case like this one, the number of chips in a cookie is described by the Poisson distribution. The mean will be 10 chips, since we are using the Poisson distribution, the standard deviation will be the square root of the mean or 100.5=3.16, or about 3 chips. One way to ensure a more even distribution of chocolate would be to divide each chip into 10, so we would have 10,000 smaller chips in a batch. On average each cookie would now have 100 chips and the standard deviation would be 10. Plus and minus one standard deviation is about two thirds of the data, so two thirds of the cookies would have +/- 10% of the desired amount of chocolate, a much better result. If we divided the chips into even smaller sizes, we would further tighten the distribution.

How does any of this relate to solder preforms or solder paste? In the new world of lead-free solder pastes, where it is common to have 3 or 4 alloying elements, some in very small concentrations, it can be difficult to control the concentration of the alloying elements throughout a sample of the alloy. The limits of mixing are just part of several processes that are required to assure that a modern lead-free solder has a consistent formulation. These are some of the topics you should discuss with your solder supplier to ensure consistency in any solder alloy you purchase. Asking to see assay analysis of a solder alloy is often a good idea, too.

Cheers,

Dr. Ron

 

Best Wishes,

Dr. Ron

Measuring Void Content

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A reader writes: Dear Dr. Ron, I need to measure the void content of an alloy. Is there an easy way to do it?

After a little thought, it occurred to me that the densities of the voided and unvoided material will likely hold the answer. I derived the result below. Assuming we know the density of the unvoided material, we can measure the density of the voided material with the Wet Gold Technique, discussed in recent posts, if the voids are not connected (closed cell.)  If the voids are connected (open cell), you could machine the foam to the shape of a rectangular parallelepiped and determine the density of the foam as the mass divided by the volume.

As an example, let’s say you have a closed cell aluminum foam. We use the wet gold technique to measure its density at 1.5g/cc. The density of solid Al is 2.7g/cc.

So the volume fraction of voids is:

Sadly, this technique could not be used to find void content in solder joints, or in BTC (e.g., QFN) thermal pad connections (which are so handily mitigated by using solder preforms.)  The derivation for the above equation follows:

 

Best Wishes,

Dr. Ron

Cool on Global Warming Idea

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Folks,

I am a global warming skeptic. This term, however, requires some explanation. I believe in climate change. The climate is always changing. However, I don’t think it is clear that the world has been getting warmer in the last decade. I also am not convinced that humans are the main drivers of whatever  climate change has occurred. The following explains why.

Point 1: For the Last 12 years the World Not Getting Warmer

The global warming scenario that exists today is that human emissions of carbon dioxide are the main reason that the climate is warming.  So, it is natural then to ask, is the climate really warming?  One look at USA Today’s cover story “Why You Should Sweat Climate Change” on March 1 would appear to settle the story.  Just look at  Figure 1 below.

Figure 1. Graph from USA Today March 1, 2013.

A quick scan of the graph shows 55.34°F last year and 50.56°F in 1895, a 5° increase.  Wow! A little closer analysis reveals that these temperatures are individual data points. If you look at the years 1900 and 2010, you get 53°F for both years, essentially no change. The thick red line is the long term trend and admittedly it increases from about 51.3°F to about 53°F in the 117-year period.

Note the icon in the upper right corner. It shows the globe with a dramatic upward trendline. However, this causes you to now note that this graph is for US temperatures, not world temperatures. What was the world temperature like? As this thought crosses your mind, you remember that 2012 brought Europe its coldest winter in recent memory. So you go on the internet and find out that 2012, for the world,  was the ninth hottest year on record.  Scary.  But then you think, “Wait a minute, that means that eight years were hotter.” So you wonder, what do the last 10 or so years look like for world temperatures.  The graph is below in Figure 2:

Figure 2. World Temperature 2001-2012. Graphed by Dr. Ron

 

Note that for the past 12 years, the trend is flat (actually a little down). Where are all of the headlines sharing this important information? So it is not clear that the world is continuing to get warmer.

Am I the only one that finds it troubling that the media seem to universally tout the scary stories about global warming, but don’t seem to mention obvious counterpoints such as the graph above?  This information is profoundly important.

Point 2: In the Past, Nature Along has Delivered Stunning Climate Change by Itself

I am writing this post from my home Woodstock, VT. I look out my window and view two beautiful, large rocks, each about the size of a house. These monoliths were likely left as the glaciers in the last ice age retreated, these rocks probably originated in Quebec.  Woodstock was under thousands of feet of ice during the last ice age, Canada was completely under ice. New York State’s Long Island is a glacial terminal moraine. The extent of the ice coverage is shown in Figure 3. However, the forces of nature alone, raised the temperature of the earth by 12°C(with no help from mankind), melting the glaciers and allowing me to live in the Green Mountain State (Vermont = Ver (green) mont = mountain, in French.)

 

Figure 3. The Extent of the Ice Coverage in the Last Ice Age http://www.iceagenow.com/

The natural processes that caused the warming are many.  They include the precession of the earth on its axis, variation in the output of the sun, changes in the ocean and atmosphere, and others. These processes  have resulted in the past temperature changes as shown in Figure 4.

Figure 4. Temperature of the earth in the past 800,000 years

This figure shows as much as a 20°C (36°F!) temperature swing produced by nature alone.  The change in world temperature between 1900 and 2010 would be about as thick as the line in this figure.

I find the proposition that the main driving force in global warming (if it is occurring)  being human produced CO2 alone is hard to accept, when we see what mother nature has given us in the past.  It would be similar to someone taking the position that the only thing that affects stencil printing quality is the stencil.  When others point out that it might be the solder paste, or the print head, or separation speed, etc., they are shouted down as being unscientific.

Point 3: It was Warmer in the Middle Ages than Today

The United Nations commissioned a panel to study climate change in 1988.  The Intergovernmental Panel on Climate Change (IPCC)  was established.  In 1990, the panel came out with an assessment of past world temperatures as shown below in Figure 5.  The estimating of temperatures before the mid 1800s is difficult due to lack of records and thermometers before this time.

Figure 5. The First IPCC assessment of world temperatures, 800AD to present

There is some argument that the Medieval Warm period and Little Ice Age were local events, however they clearly existed and profoundly affected much of the Northern Hemisphere. But more recent temperature IPCC plots lose them, as seen in Figure 6. The Medieval Warm Period enable the Vikings to settle in Greenland and red wine to be grown in England. When the Little Ice Age came, the Vikings had to leave and England has not been as warm since.

 

Figure 6. Third IPCC temperature assessment. Note the Medieval Warm period and Little Ice Age disappear. Because of the abrupt change in temperature after 1900, this graph has earned the moniker, The Hockey Stick Graph.

The controversy over the Hockey Stick graph  is interesting reading and is the source for Figures 4-6.

In 2003, MacIntyre and McKitrick presented a detailed criticism of the IPCC 3rd Assessment’s Hockey Stick Graph in Figure 6 . I find their criticism compelling.

I could go on and on,  but to summarize why I am a global warming skeptic:

  • For the  past decade the world has not gotten warmer
  • Natural forces overwhelm CO2 as a driving force for climate change
  • Sloppy science is behind the hockey stick graph

Please share your science- and fact-based comments.

Cheers,

Dr. Ron