In Electronics Manufacturing, Does Cpk =1 Yield 66,800 DPM?

As Patty was walking past the Professor’s office on her way to see Pete and Rob, she decided to drop in.

“Professor, I got the strangest phone call. A man claimed he had invented a machine that could create energy,” Patty began.

“Tell me about it,” the Professor chuckled.

“Well, he correctly noted that, when he took his kids to the beach, a submerged beach ball pushed up with a lot of force. So, he developed a technique to extract the energy produced when the ball is released,” Patty explained.

“Let me guess,” the Professor offered. “He then developed a technique to continuously extract energy; an energy producer of sorts.”

“Exactly! How did you know?” Patty responded.

“Well, I have been here about 40 years, and I have had forty such calls,” the Professor said.

“Tell me the details of your call,” he continued.

“There would be a box of small mass with a generator and pump inside; the generator and pump occupying little of the volume of the box. The box would be filled with water at the top of a lake and would then would sink to the bottom. Once the box was at the bottom, the water would be pumped out and the buoyancy would cause the box to rise. A rope would guide the box on its up and down journey and the generator would spin as it travels up the rope, hence generating electricity. The cycle would be repeated over and over and, in a sense, become a power plant,” Patty explained.

“And the problems are?” the Professor asked.

“I told him that it violates the laws of thermodynamics, and that I could make some calculations that would show that it would not work. Basically, the amount of energy required to pump the water out is greater than what the buoyancy would generate, considering friction, etc.,” Patty replied.

“His response?” the Professor led.

“My sense is that he thought he could make it work, in spite of the physics,” Patty answered.

“In my experience, that is always the response. Probably my most troubling experience was a chap who convinced a small venture capital firm to advance him about $3 million. He had a machine that, he claimed, continuously extracted energy out of the earth’s magnetic field. The biggest shock to me was that the leader of the venture capital firm was a graduate engineer who had retired as COO of a Fortune 50 company. I still haven’t figured out how such an accomplished person could not see that an energy-producing machine is not possible,” the Professor expounded.

“What was the upshot of all of this?” Patty asked.

“Well, they didn’t pay my consulting fee when I explained how it couldn’t work,” he chuckled. I checked a few months ago and the company’s website is down,” the Professor replied.

“The people that are into this folly don’t even realize that, if an energy-creating machine could be made, it would be the greatest discovery in history,” the Professor went on.

After a few more minutes of this discussion, Patty resumed her short walk to Pete’s office. Rob was already there.

“Looks like Mike Madigan needs us again. Did you see the email he sent us?” Pete asked.

“No, what’s up?” Patty and Rob said in unison.

“Something about Cpk,” Pete answered.

Patty reached for the phone to set up a conference call to Mike.

As she dialed, Patty admonished, “Now remember you two, good manners. No laughing at any of Mike’s questions.”

“Yes, ma’am,” Pete and Rob said in unison.

Mike’s secretary answered and said she would put them right through.

After a few pleasantries, Mike got to the point.

“Remember the tolerance analysis and specification that you did for passive resistor and capacitor length?”  Mike began.

“Yes. We were all involved in that project,” Patty answered.

“So, it is a Cpk = 1, or a Three Sigma spec, right?” Mike asked.

“Sure,” Patty, Rob, and Pete answered in unison.

“So, what percent of parts should be out of spec?” Mike asked.

“Let’s see … Three Sigma is 99.73% of parts in spec … so that would be 0.27% out of spec,” Pete calculated.

“Well, they are shipping us 5% out of spec parts and claiming they are better than Three Sigma, or a Cpk of 1, because they used a recently published graph, that said a Three Sigma, or Cpk = 1, process was 6.68% of parts out ot spec. I just sent it to all of you,” Mike said.

Pete opened the email and showed it to Patty and Rob.

“I’ll be darned! It does say that a Cpk = 1, or Three Sigma, has a defect rate of 66,800 defects per million or 6.68%,” Rob groaned.

“I’ll bet it has to do with the definition of ‘Six Sigma,’” Patty opined.

A look of recognition came over Pete and Robs eyes.

“What do you mean by the definition of ‘Six Sigma?’” Mike asked.

“We have all heard people claim that ‘Six Sigma’ is 3.4 ppm out of spec. Actually that’s a 4.5 sigma process. This definition allows a drift in the average of 1.5 Sigma that knocks the Cpk down to 1.5.  True Six Sigma is a Cpk = 2 and is 0.002 ppm parts out of spec,” Patty replied.

“I’m a bit confused. But, let me show you some of the length data for 0402 passives,” Mike said.

“We measured them metrically so the length should be 1mm +/-0.1, Three Sigma.  Instead, it is more like 1mm +/-0.1, Two Sigma. That’s a little more than 5% outside of the spec,” Mike continued.

A Minitab Analysis of the 0402 Length Data.

“Give us some time to sort it out,” Patty suggested.

Is a Cpk of 1, or a Three Sigma, process really 66,800 ppm (6.68%) out of spec?  Will Patty and the crew figure out what’s going on?

Stay tuned…


Dr. Ron

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In Memory of Steve Chidester

Steve Chidester was a class act.

EDA software can be a cutthroat place, but good luck finding someone who would even think of saying something unkind about Steve.

Known inside Cadence as “Mr. Allegro,” Steve could as well have been called Boomerang for the way over three decades he always returned to the software company. Steve did three stints in all at Cadence, totaling 17 years. He had only recently returned to the company when he passed away from cancer last week at age 55.

While I had met Steve years ago, I didn’t really get to know him until he joined Zuken as head of product marketing in 2010. He was instrumental in getting the IPC-2581 data transfer format off the ground after 40-plus years in the mire.  At Steve’s invitation, I spoke on the topic at Zuken Innovation World that year, although I resisted his repeated urging to present at the company’s user conference in Tokyo. Something about not being fluent in Japanese always held me back.

Little details like that could never stop Steve, however. He was an eternal optimist, never one to get down either on a situation, himself or others. Colleagues tell me that even after learning, in late November, that he had a particularly aggressive form of cancer, he downplayed it, saying it was treatable.

He spoke often of his family — he had nine children plus several grandchildren. That always appealed to me as well, as I like going beyond the regular job-speak and getting to know the folks I work with around the industry.

In an industry filled with generous people, Steve was a particularly kind soul. I will miss him dearly.

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Is This the Future of AOI?

Engineers at MIT have designed an atomic force microscope that scans images 2,000 times faster than existing commercial models. With this new high-speed instrument, the team produced images of chemical processes taking place at the nano-scale at the rate close to real-time video.

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Wicked Wicking

This PCB assembly challenge involved attaching a solar panel to one side of a pad using solder paste with a pass through an SMT reflow soldering oven.

Figure 1.

Solder wicking through the unmasked vias to the back side forms unacceptable “bumps” on top of the vias.

The attachment or bond itself wasn’t the issue; but after the first trial runs, it was clear that solder wicking through the unmasked vias was going to be. Solder would wick through the unmasked vias to the back side and form “bumps” on top of the vias.

These bumps made the surface nonplanar and of course were unacceptable. It wasn’t an issue of using excess solder paste. But the “wicked wicking” had to be stopped, or at least prevented.

Figure 2.

Kapton tape is applied to cover the unmasked vias; it will block the molten solder from leaking through.

But how? Clearly, to keep the solder where we wanted it to remain during reflow, we had to find a way to prevent it from wicking up, collecting at the opposite ends of the vias and forming bumps. We had to find a solution that was simple, temporary, and tolerant of reflow soldering temperatures. The answer was Kapton polyimide tape, a familiar product to PCB assemblers for many years, and a material that does not degrade at reflow temperatures.

Kapton tape was applied to cover the unmasked vias in order to block the molten solder from leaking through the vias to the back side during reflow. After reflow and cooling, it was a simple matter to peel off the tape. This temporary masking solution worked; there were no more solder bumps on the back side of the assembly, and the cost of the fix in terms of time and material was very low.

Figure 3.

Figure 3. This temporary masking solution worked; there are no more solder bumps on the back side of the assembly.

Roy Akber


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Users Could Find New CES ‘Wearables’ Painfully Restrictive

The early reports from CES indicate wearable devices continue to be the hot item. Among the early headliners:

  • Samsung’s WELT wellness belt, which is really a backpack that charges phones via solar panels, among other things;
  • Samsung’s Smart Suit, which to my view does fairly mundane tasks like like unlocking your phone when you take it out of your pocket;
  • Samsung’s lab also made a golf shirt that can sense the weather and UV ratings;


    Samsung’s Smart Suit

  • Under Armour’s Healthbox, which features an activity tracker, chest strap and smart scale; and Samsung’s Body Compass 2.0, a sensor-laden workout suit that performs similar tasks;
  • MadRat’s Supersuit, which is designed to play laser tag and other such games in a closed space;
  • MadRat's SuperSuit

    MadRat’s SuperSuit

    Also coming from UA, a smart running shoe that tracks movement and lets users know when the shoe should be replaced.

What these devices have in common is the ability for users to track their activity — and by extension, their wellness — in real-time and on multiple platforms including their smartphones. What they can also do is amass a terrific amount of data that may or may not be used for their original intended purposes. In short, if you can collect and review the data, so can someone else.

Consider: What if health insurers were to require policyholders to wear devices that tracked such details? And what if your insurance rates were to climb simply on the basis of a weekend ice-cream binge? What if auto insurers could tell that you had activated your cellphone while in a driving, and could cancel your policy on the basis of that information? What if it was learned that you habitually played 18 holes during high ozone days?

While the ability to monitor one’s health using actual real-time data is eye-opening, are we opening a door to such data being misused, or at least, applied in a fashion that could have very real and life-changing implications for the user?


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Using the Coffin-Manson Equation to Calculate Thermal Cycles


Let’s look in on Patty and friends ….

Patty, Rob and Pete were headed to their regular monthly meeting where they, along with the Professor, discussed a book they were all reading.  This month’s book was about General Leslie R. GrovesRacing for the Bomb

“This was one of the most interesting books we have read,” Pete said starting the meeting.  “I think most people are aware of the technical genius of the scientists involved in the Manhattan Project, such as J. Robert Oppenhiemer and Richard Feynman, but few appreciate the contributions of Gen. Groves,” Pete continued.

“I agree,” Rob said.  “Without Grove’s orchestrating of the overwhelming number of small and large details of the program, it would have taken three times as long,” he went on.

“Right!” the Professor chimed in. “He set up a $20 billion enterprise to produce the components of the bomb in less than three years.  Who else could have done that?”

“One of the things that I found almost comical was that he was so good at the secrecy of the project that his family had no idea he was working on the bomb until it came out in the newspapers,” Patty exclaimed.

The four book club members chatted about the book for about 20 more minutes.  Patty felt her cellphone vibrate.  It was a text from Mike Madigan.

“Rob, Pete, it looks like we may have another assignment from Mike. He wants us to call, so let’s go to my office,” Patty suggested.

Even though the three of them were all at the engineering school at Ivy U, Mike Madigan, the CEO of ACME, established a blank contract with them to do part-time consulting.  Part-time consulting is quite a common thing in the academic world as it helps the profs and technical staff keep current and also earn a little money.

Patty called Mike’s number and activated the speakerphone.

“We have a customer who we assemble TVs for.  Each TV goes through 10,000 on/off cycles in its field life.  The temperature change from these on/off cycles is from 20°C to 50°C.  We are performing thermal cycle testing of the PCBs from 0°C to 100°C.  How many thermal cycles will we need to perform to equal the 10,000 field cycles?” Madigan asked.

Patty chuckled to herself as she had just solved a problem like this for a reliability workshop that she was developing. So, the technique was fresh in her mind.

“You need to use the Coffin-Manson equation,” Patty explained.

“Whoa!” Mike chuckled, “Is the problem so serious that we need to worry about coffins?”

“Coffin-Manson is used to relate strain to temperature changes. It will help us to calculate the right number of cycles,” Rob chimed in.

Rob, Patty, and Pete all got calculators out to see who could get the answer first.  Pete won the contest.

“I get an acceleration factor (AF) of 25,” Pete announced victoriously.

“Agreed,” Patty and Rob sighed in unison.

“The equation is quite simple,” Patty shared.  See the figure below.




“The Coffin-Manson acceleration factor for lead-free solder, m, is about 2.7,” Patty finished.

“So, you need to perform about 400 (10,000/25) cycles in the test chamber,” Pete said.

“Wow! I’m really relieved,” Mike said, “I thought it might take 2,500 thermal cycles or more.”

“There is no way we had enough time for that number of cycles, but 400 is easily doable,” Mike concluded as he sighed a breath of relief.

The four of them chatted for a while more and then went their ways after having mastered another electronics assembly problem.


Dr. Ron

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Too Close for Comfort

This is a little bit like the old college prank of trying to see how many kids can squeeze into a telephone booth. Pretty soon everyone’s too close for comfort!

In this PCB assembly challenge, someone made a mistake and created a layout for rows of dual-flat no-leads (DFN) SMT packages without taking into account the size of the component bodies. The footprints are too close together, and the bodies of the components are touching.

Because they don’t all fit, as the packages are lined up there isn’t enough room, and alignment issues develop for some of the IC locations. They’re forced off their footprints, while others appear to be acceptable.

Figure 1

Figure 1. With DFN footprints too close to one another, component bodies are actually touching and causing alignment issues, literally forcing others off their footprints.

Figure 2

Figure 2.

As can be seen from the photos (Figures 1 and 2), the crowding causes alignment issues for locations IC1, IC5, IC7, IC9, IC13, and IC15. Locations IC3 and IC11 seem fine.

What can be done? It’s too late to redesign and order new PCBs, and there is no possibility of shrinking the dimensions of the components.

Figure 3

Figure 3. Removal of components in locations IC5 and IC1 have allowed the rest to fit properly.

Luckily, the customer had a solution that worked: removal of the components in locations IC5 and IC1 (Figure 3). This permitted the remaining parts to fit correctly; it made “breathing room” for the rest, and best of all, was accomplished without compromising the functionality of the circuit.

Roy Akber


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Predictions for the End of the Decade

Half a decade ago, back in January 2010, I wrote up a list of predictions for the end of the decade. You can read that list here. It’s still 2015, so I can plausibly say that we’re halfway there, which is a good time for a status update.

0000: In 2010, I said: By the end of the decade, 50% of all passives will be embedded passives and 20% of all PCBs will have 90% or more of their passives embedded.

In 2015, I say: This doesn’t look to be coming true, but it still might. As mobile devices and wearables get smaller, or more powerful, more electronics will need to be stuffed in progressively smaller areas. Those passives need to go somewhere. That somewhere could be into the PCB, or into the chips. I think the PCB is more likely.

0001: In 2010, I said: By the end of the decade, quad stack PoP (package-on -package) will be commonplace.

In 2015, I say: Quite likely. Double layer POP is showing up on low cost devices, like the $5 Raspberry Pi Zero. If it can go there, it can go pretty much anywhere. It won’t be long before double stacking won’t be enough. Although, the layers may end up being inside the chip package, rather than individual chips as layers.

0010: In 2010, I said: By the end of the decade, Each individual human will have their own IP address. Several of us will have more than one. That way, we can jury rig accelerometers into our hands and feet so we can wirelessly know where each of our extremities are at all times. Cats will have them too.

In 2015, I say: Yep, and then some. I already carry one in my pocket. In five years, we’ll likely see personally assigned IP addresses that won’t be device-dependent. We’ll be able to buy IP-enabled clothes, like gloves, which will do a lot more than just know where each finger is. The pet ID chips that today use NFC will be available in wireless Internet connected versions.

0011: In 2010, I said: By the end of the decade, solder paste will be used less often than not when assembling components on to PCBs.

In 2015, I say: We will be seeing welded copper, additive embedded 3D printing processes, conductive glue, and other non-solder methods of assembly, but nowhere near to the degree I was thinking back in 2010.

0100: In 2010, I said: By the end of the decade, nearly all hydraulics and pneumatics in new motor vehicles will have been replaced by electrics.

In 2015, I say: This is already well on the way. With electric and hybrid electric cars growing in numbers, and with weight and fuel mileage being such a concern, this has to happen.

0101: In 2010, I said: By the end of the decade,the first semi-autonomous passenger vehicle will be on display on the auto-show circuit. Hobbyist built semi-autonomous cars will already be on the road.

In 2015, I say: I may have missed the boat on this prediction, in the pessimistic direction. Part of it has already happened. I haven’t yet seen hobby kits, but most of the major car manufacturers have shown models. Tesla has a really good driver assist “auto pilot,” and is promising fully autonomous vehicles for sale within two years of this writing.

0110: I said: By the end of the decade, “airline pilot” will generally be a really, really, really boring job. That’s a bit of a problem.

In 2015, I say: The necessary level of automation required for this prediction to come true is already installed in most airliners. The only real question remaining, is how long before it changes from “Pilot primary, systems secondary” to “Systems primary, pilot secondary.”

0111: In 2010, I said: By the end of the decade, most military “foot action” will consist of two soldiers in command of a squad of robots and those two soldiers will as likely be in Fort Lewis, Washington as in the combat zone.

In 2015, I say: Sadly, I still think this will happen. Not sad that fewer humans will be shooting and getting shot, but sad that we as a species will still consider war important enough to be throwing large quantities of money and resources at.

1000: In 2010, I said: By the end of the decade, the president of the US will be promising health care reform as the highest priority.

In 2015, I say: Yep. The president, presidential hopefuls, senators and representatives will still see this as a hot issue. One side will be trying to make quality healthcare more accessible, the other side less. One side, more publicly funded, the other side, less. I’m not really sure which side will be doing which, but I’m certain that each side will say they want to fix it and the other side wants to destroy it. Ugh.

1001: In 2010, I said: By the end of the decade, routine bioengineering will be, well, routine. Very scary.

In 2015, I say: I’m not so sure about this one. When I wrote it, I was thinking that home bioengineering would be happening and a class of bio-hackers would be emerging. That may still happen, but it won’t be common. Governments, agriculture, and medicine will be doing a lot more of this, but I’m not sure the term “routine” will be accurate.

1010: In 2010, I said: By the end of the decade, the 2019 recession will be looming large and all the people who have forgotten about the 2009 recession and the 2001 recession and the 1985 recession and the 1975 recession … will be freaking out again.

In 2015, I say: Is there any doubt? Does this ever not happen?

1011: In 2010, I said: By the end of the decade, lead will be gone from 98% of new electronics. Bummer.

In 2015, I say: Exemptions are going away. This will happen.

1100: In 2010, I said: By the end of the decade, four of the substances that replaced the substances removed from electronics due to RoHS and similar regulations will have been found to be significantly more harmful to the environment and the people recycling the materials than are the substances that they replaced.

In 2015, I say: I was being tongue-in-cheek, but it still might happen. The only caveat is that if it does happen, the data will be so obscured by politics that it likely won’t be possible for anyone to come to an informed opinion.

1101: In 2010, I said: By the end of the decade, the world of intellectual property will be in even more of a mess than it is today. Virtually everything will be accessibly for easy theft and cheap replication. (This is pretty much a big “duh.”)

In 2015, I say: This is still well on the way. Any industry that designs things will need to adapt to keep competitive. The patent world will still be a mess. Copyrights will be more of a litigation attack weapon than a protection tool. The best defense against pirates will be faster innovation. On the positive side, a lot of IP sharing will be intentional (by the inventor) and many businesses will be built based on collaborative innovation.

1110: In 2010, I said: By the end of the decade,building your own multipurpose robot will be as easy as building your own PC was in 1988. Hardware components and operating systems will be off the shelf, but standards will be pretty loosely defined, interoperability will be more theory than reality and applications will be sketchy and buggy.

In 2015, I say: This will happen, but it may be a little later than the end of the decade. The technology will very much exist for this to happen, but the capability of the hardware will probably be advancing so fast that even the limited amount of standardization needed for this won’t be possible.

1111: In 2010, I said: By the end of the decade, still no flying cars and personal jet packs, dadgummit!

In 2015, I say: And, still no real hover boards.

Duane Benson

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The Top 10 in PCD&F

Yesterday, we reported the top 10 best-read articles published by CIRCUITS ASSEMBLY in 2015. Today we list the best-read articles from PCD&F.

The list includes features that were published for the first time in calendar 2015. Rankings are based on web site hits, and do not include — for obvious reasons — the number of reads in the print version of the magazine.

1. “Embedded Passive Technology Materials, Design and Process,” by Hikmat Chammas
2. “Beyond the Vault: The Evolution of PCB Design Archiving,” by John McMillan.
3. “01005: Size Does Matter,” by Arbel Nissan.
4. “Trace Current/Temperature Relationships,” by Douglas G. Brooks, Ph.D. and Johannes Adam, Ph.D.
5. “Microsectioning of Laminates,” by Karin Rudman Prieto, Ph.D., Peg Conn, Lizabeth Lagos and Charles Lehmann.
6. “The Changing Face of the Hardware Design Engineer,” by Steve Hughes.
7. “Refining Lean NPI at Optimum Design Associates,” by Randy Holt.
8. “The 3 Challenges Facing the Future of PCB Design,” by David Wiens.
9. “How Hot Is My Via? (Cooler Than You Think!),” by Douglas G. Brooks, Ph.D. and Johannes Adam, Ph.D.
10. “In Search of Greater Tolerance,” by Peter Bigelow.

There was a definite advantage for articles that were published near the beginning of the year. If we adjust for timing, a feature on field solvers authored by Dr. Eric Bogatin and published just last month more than likely would have made the top 10. And although not reflected here, there was tremendous and perhaps disproportionate interest in flex circuits, given the smaller audience involved to-date in flex, with pieces by Mark Finstad (“Designing Flex Circuits For Wearable Electronics“) and Ben Jordan (“Designing a Successful High-Speed Rigid-Flex PCB“) just missing the top 10.

As always, we are grateful for our loyal readers and the many authors who contribute their expertise each month.

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For the past several years, we have taken a few moments at year-end to look back at the best-read articles of 2015.

The list includes features that were published for the first time in calendar 2015. Rankings are based on web site hits, and do not include — for obvious reasons — the number of reads in the print version of the magazine.

We’ll start today with the top 10 from CIRCUITS ASSEMBLY. Tomorrow we will list the best-read articles from PCD&F.

1. “How Clean is Clean Enough?” by Terry Munson, Paco Solis, Nick Munson, Steve Ring and Evan Briscoe

2. “01005: Size Does Matter,” by Arbel Nissan.

3. “Designing Flex Circuits For Wearable Electronics,” by Mark Finstad.

4. “Depaneling of Circuit Boards,” by Ahne Oosterhof and Thomas Nether.

5. “What You Cannot See Can Be Hand Soldered,” by Paul Wood and Bob Wettermann.

6. “A New SPI Tool for Defect Prevention,” by Chrys Shea.

7. “Zooming in on Digital Microscopes,” by Chrys Shea and Kristoffer Tømmergaard.

8. “China in Charge, by Dr. Hayao Nakahara.

9. “US or Mexico: Which Option Makes Most Sense for Your Project?” by Joe Villanueva.

10. “Cost/Benefit Tradeoffs of Capacitor Part Size vs. Manufacturing Efficiency,” by Chris Reynolds.

As you can see, a mix of technical and business-related pieces made up the top 10 this year. Interest was high in cutting-edge technology (multiple pieces on 01005s, wearable flex circuitry), but tutorial-type pieces on conventional technology held its own as well (cleaning, circuit board depaneling).

As always, we are grateful for our loyal readers and the many authors who contribute their expertise each month.

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