Indicating Polarity on Diodes

Everyone knows which way current flows through a diode. Right? Of course they do. Diodes only permit current to flow in one direction.

Well, sort of.

In the case of your garden variety rectifier, barrier diode, or LED, that’s true. That line of thinking leads a lot of people to assume that you can indicate diode polarity by putting a plus sign “+” next to the anode.

Here’s why you can’t.

Zener and TVS diodes have a breakdown voltage. They are put in the circuit with their cathode on the positive side. In that configuration, they don’t conduct unless the voltage rises above their breakdown point. Zeners and TVSs are used for regulation, transient suppression, and things of that sort.

But wait! There’s more!

Regular diodes can be pointed backwards too. Anytime an inductive load is switched, like a solenoid or motor, you need a flyback diode to protect the switching logic. A MOSFET switching a solenoid on and off is a good case to look at.

When the MOSFET turns off, the current in the solenoid coil starts to drop. As it starts to drop, the magnetic field generated by the current flow starts to collapse. The collapsing magnetic field generates an opposite current, referred to as flyback, or back EMF.

To save your silicon switching device, you put a flyback diode across the coil, or motor, terminals, pointing backwards from normal current flow – with the cathode pointed toward +V. Doind so shorts the flyback current back into the coil, preventing damage to the MOSFET. These are typically Schottky diodes, but can be ordinary rectifier diodes.

A “+” plus sign alone, doesn’t tell anyone anything. For more information on what to do, read this post. Just for fun, read this post too.

Duane Benson
Diodes. Not just for breakfast anymore

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Using the Newest Gen Arm, Part III

The continuing saga of the 0.4 mm pitch KL03 ARM microcontroller. If you haven’t yet done so, read part I and part II.

Today, I have a look at the good, the bad, and the ugly – or more accurately, the good, and the bad and ugly. As I expected, I was quite pleased with the job done here in house. The board is nice and clean, the parts are well centered, and the solder joints are solid. No surprise here.

Here’s a top view of one we did here in Screaming Circuits:

Next, I’ve got one that I did at home. It actually surprised me and came out better than I had expected. Here’s a top-down view of the one I did at home with home-grade tools (No, I didn’t intentionally make it look bad. The board surface is just a bit shinier than the one above.):

Of course, “better” is a relative term. I didn’t say good. I could call this both bad and ugly. I did manage to center the parts quite well — that took a lot of careful nudging with sharp tweezers and and an X-Acto knife blade.

All of those little round shiny spots are solder balls. That’s what happens when you get too much solder on the board, get solder off the pads, or have the wrong reflow profile. They might look harmless, but if there are too many under the chip, the connections could be shorted.

The fillets on the 0201 capacitor are a little lean on solder in the one I did, and there’s a solder ball on the right side, but, again, it looks better than I expected.

Next time, I’ll post the x-rays and show what’s under the hood.

Duane Benson
Carburetors, man.
That’s what life is all about

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Using the Newest Gen Arm, Part II

I’m a bit behind in my blog work — well, way behind, actually. I started this series back in January with the intro post.

Here’s where I am right now:

  1. I have three different sets of PCBs.
  2. One set, I took home to see if it’s possible to solder a micro-BGA at home. (As someone working at a car manufacturer might want to see if they could balance a crankshaft at home, for fun)
  3. Two sets, from our partner, Sunstone Circuits, are here in my desk with parts, ready to go through our machines.

After I’ve got all three sets built, I’ll have them x-rayed to see how they look under the hood. Finally, I’ll solder through-hole headers on and fire up the chips to see if the shared escape system works.

Here’s one of the boards without access to the inner pads:

And, here’s the shared escape:

The main concern I have is that Reset is on one of the inside pins (B4). I’m not sure if I can get the chip to a state where it will operate properly without unobstructed access to reset.

The routing I’ve chosen is probably the only possible option for reset. Pin A4, right above, is used for the single-wire debug (SWD) clock. I’m assuming that can’t be shared. B5 is Vdd, so that’s out. It might be possible to go down. C4 defaults to one of the crystal pins, and D4 defaults to a disabled state.

In the route I’ve chosen, B3 is an ADC input, so it should start out high-impedance, and therefore not interfere. A3 defaults disabled, so it won’t get in the way.

Next step: solder time!

One other thing – The images above show non-solder mask defined (NSMD) pads. Those are standard for BGAs 0.5mm pitch and higher. This part is 0.4mm pitch. Some manufacturers recommend solder mask defined pads (SMD) for 0.4mm and smaller. I’m actually testing several pad styles: SMD, NSMD and solder mask opening = copper.

Duane Benson

Run it up the flag pole and see who solders

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API’s Changing of the Guard

API Technologies named a new president and CEO today, and, like his predecessor Robert Taveres comes from the component side.

That makes sense because API derives much of its revenue — and profit — from making RF/microwave components. The firm has made headlines of late, however, because its lead shareholder is also the largest owner of IEC Electronics, an API competitor on the EMS side. And that shareholder, the equity group known as Vintage Capital, has been engaged in what turned out to be a victorious proxy battle for the leadership mantle of IEC.

With a new board in place at IEC, and an EMS veteran in charge, will this mean a sale of API’s EMS business to IEC is in the offing?


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Component Footprint Rotation, Part II

I’ve noticed that a lot of CAD library footprints for two-pin polarized parts have pin one pointed up as zero degree rotation. According to IPC, pin 1 pointed to the left is zero degree rotation.

Why is this such a common error? I can’t be certain, but I have a pretty good idea.

Surface mount parts, as everyone knows, generally come in reels of tape. It stands to reason, that the parts would be placed into the tape at a standard zero-degree rotation. They generally do. Before putting a perplexed look on your face, take a look at the image below.

When looking at the tape, it’s a pretty natural thing to pull it out and hold it horizontally – with pin 1 up – perpendicular to our angle of vision. Makes sense. It’s not a stretch to look at this strip of tape and end up assuming that pin one is up at zero rotation.

However – the machines are the ones being spoken to. Not humans. The machines get the parts in line with their line of vision. That puts pin one on the left.

Makes more sense when you look at it this way. Running into the machine, pin one, at zero rotation, is on your left.

For more to the part rotation story, tune your browser dial to here. Or just scroll down a little bit. It’s right below.

Duane Benson
The long and winding reel leads to your PC board. Not your door.

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Component Footprint Rotation

Before we (or any old assembly house) go about putting surface mount parts on a board, we need to program our assembly robots. I’m oversimplifying, but essentially, the machine program needs to know the X / Y coordinates, relative to the board origin (which is the lower left-hand corner), the part rotation, and the side of the board.

In years past, we needed a centroid file (AKA pick-and-place file) containing all of that information. In some cases, we still need the centroid, but not always. Today, we can get the same information from ASCII CAD files, ODB++ CAD files or Eagle .brd files. You only need a centroid if you send us your board files in Gerber format.

If you do send us a centroid file, you no longer need to worry about rotation. The IPC has defined the zero degree orientation, as well as proper rotation direction, but too many part footprints set the zero degree at different angles. We can’t rely on the data.

While we have to ignore rotation and figure it out with other means, we still do strongly recommend that you follow IPC standards when you make your own footprints. The illustrations below show how footprints are supposed to be oriented.

Duane Benson
There’s no earthly way of knowing
which direction we are going
There’s no knowing where we’re rowing

Package origins

Passives orientation r2

Chip rotation

Quad and BGA

Three-pin parts

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Hats Off to Gary

Congratulations to Gary Ferrari, who last month became the 33d person to gain induction to the IPC Hall of Fame. For printed circuit board designers, this is something of a symbolic victory, as Ferrari is just the third designer (after Dieter Bergman and Vern Solberg) to make it in the IPC Hall.

Ferrari, who has been an occasional contributor to PCD&F over the years, needs little in the way of introduction to the current generation of designers, in the US and abroad. He has his name on all the major industry design and fabrication standards, having led the development of IPC-D-275 and IPC-RB-276 (now IPC-2221/2222 and IPC-6011/6012, respectively). He, along with Bergman, helped found the IPC Designers Council and drove the certification program. Along the way, he has trained or taught several thousand engineers and designers on a variety of topics from layout to heat management to standards to fabrication and assembly. While not the person whose name you will see on a book, Ferrari is still one of the first phone calls anyone with an engineering problem is likely to make.

The timing is bittersweet in that it occurred just months after the death of Bergman, Ferrari’s longtime friend and colleague. Still, it is a long time coming for one of the true iron men of the industry. I am thrilled for my friend.

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Electronics Assembly Process Optimization

Mike Madigan was not used to feeling intimidated.  After all, as the CEO of ACME, a multi-billion US dollar EMS company, he was used to doing the intimidating.  However, he had just finished a meeting with the CEOs of his two biggest customers and it was a disaster.  They asked to “do lunch” with Mike and, after this event, Mike’s stomach was churning.  If Mike was honest with himself, if he was them he would have been tougher.  But, it was their teasing demeanor, punctuated with laughs and jokes, that made it all the worse.

That these gentlemen had some points to make was inarguable.  First-pass assembly yields were down 4%, and Mike’s answer, that it was because the technology was more challenging to assemble, did not fly.  They told him to get that 4% back or they will find a company that can.

Both of these gents had been process engineers when they were younger, so they “knew the ropes.”  In a recent audit of one of ACME’s facilities, they found one process engineer, responsible for the stencil printing process, that didn’t know how to run the stencil printer. And this lad also could not locate the solder paste spec.  Additionally, he could not explain what “response to pause” was.  Another process engineer did not know how to match the reflow profile to the solder paste spec (after they finally located the spec). Mike’s answer, that ACME’s recent growth made it hard to keep the training of the engineers up to snuff, only made things worse.

When asked what percent of his engineers hired in the last two years were SMTA certified, Mike didn’t know.  He expected it was 0.

Then, one of the CEOs said, “Things seemed to be much better when you had that Advanced Processes VP. What was her name? Patty something or other?”  That was a big part of the problem. Patty Coleman was gone and, with her departure, things had gone to h#!!.

Mike thought of asking Patty to fix things, but that would be unfair.  She had only been at Ivy U for a year or so and was still getting established.  Maybe the Professor could help.  Mike hoped so. The CEOs wanted a plan in two weeks.

Ten days later…

Patty had just finished getting ready for a meeting with her husband Rob, Pete, and the Professor.  Ten days ago, the Professor asked if they could help him develop a software tool that would be used by ACME as a self-audit of their practices related to electronics assembly.  The Professor said it was a request from Mike Madigan himself.

Patty had a little time before the meeting, so she decided to check her email.  Suddenly, she was disturbed by a knock at the door.

“Professor, we wanted to ask you a question about probability. Is now a good time?”, a young lad who looked 11 years old asked.

“Sure.” said Patty.  “But tell me your names first.”

“Oh!, Sorry! I’m Henry Finn. But everyone calls me ‘Huck’. And this is Chris Jenkins.  We’re both sophomores.  You spoke about statistics at our Introduction to Engineering Class a few days ago. We’re hoping you can settle an argument,” Finn began.

“What is it?” Patty asked,

“Well, Huck says that since the Patriots are one of 32 teams in the NFL, the chances of them winning 4 Super Bowls is (1/32)^4 = 9.5×10-7, or about one in a million – if they had only an average skill level.  I think it is more than that.  Huck says the rarity of them winning four Super Bowls shows how much above average they are,”  Jenkins jumped in.

“Your analysis is not quite right. You calculated the likelihood of 4 wins in a row. They have won 4 out of the last 14 Super Bowls,” Patty said. Patty was on top of the Patriots stats as she was a big fan.

“To perform the analysis, you have to use the Binomial Distribution.  Let me see if I can calculate it using Minitab 17,” Patty said.

She went to her laptop and, in no time, had a graph that explained the problem.

“So, the chances of a team possessing only average skill winning 4 out of 14 Super bowls is less than 1 in a thousand.  I’ll leave it to you two to decide what that means,” Patty summed up.

Patty chuckled to herself as she saw the two sophomores arguing as they walked away.

She looked at her watch and saw it was time to head to the Professor’s office.

Patty was the last to arrive as Rob and Pete were already there. As she sat down, the Professor began.

“Thank you for coming.  I have incorporated all of your input and am pleased with the results.  I’m hoping that we can review the resulting web application that was developed,” the Professor began.

“Is it in English or one of the 17 other languages you speak?” Pete joked.

“English, Pete. English,” the Professor chuckled.

In reality, Patty, Pete, and Rob were thrilled to help the Professor develop this self-auditing software.  They all knew that it isn’t that often that one can help someone like him.

The Professor was only able to come up with 20 questions for the software.  Patty, Pete, and Rob increased it to 40. Pete was proud that he contributed 8 of the additional twenty questions.

The Professor flicked on his projector and displayed the first page of the self-auditing software.

“This is the first of the four sheets for the software tool.  I think Rob’s suggestion to name it ‘AuditCoach’  is a great idea.  Let’s take a look and see what we think,” The Professor said.

“I think it’s good that you have the questions about the process engineers knowing how to run and optimize the equipment.  It is surprising how many times that is not the case,” Patty commented.

“That was Pete’s idea,” the Professor replied. Pete beamed from the recognition of the Professor.

“I like the idea of making the first question count 3 times as much since it is so critical,” Rob chimed in.

“Agreed,” Patty and Pete murmured.

The Professor pressed on, “I thought it might be best to break the questions in to four categories:

  1. DfM, Processes
  2. Equipment, Materials Supply and Validation
  3. DOE, SPC and CIP, and
  4. Training and Failure Analysis.

Over the next hour the group reviewed all 40 questions on the four sheets of AuditCoach. Some minor improvements were made.

As they were wrapping up, the Professor had one last comment, “I asked Mike Madigan if he would make AuditCoach available to others.  We both thought that doing so was a good idea.”


Dr. Ron



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What Apple’s Latest Supplier Audit Says About Apple

Apple’s annual supplier audit was released today and sure enough critics on both sides are already picking through the core and going at it over whether the company is doing enough to ensure the safety and compensation of the hundreds of thousands of workers who plug away in anonymity daily making Apple the wealthiest company ever.

Apple’s latest stats show a 92% compliance rate with its 60-hour workweek, and says the average workweek was less than 49 hours. Of course, that’s as it should be: Most of Apple’s supply chain is in China, whose laws cap the work week at 40 hours and monthly overtime at 36 hours. Adding nine hours per week over four weeks per month comes to 36, which means Apple suppliers are likely often breaking the local laws.

Indeed, that’s consistent with a separate study of nearly 100 Pegatron workers undertaken by labor rights group China Labor Watch, a constant thorn in Apple’s side, which found that more than half of the its workforce performs more than 90 hours of overtime per month, with some peaking at 132 hours.

Apple essentially ignores this by trying to turn a lemon into lemonade. It now touts its ban — as of October — on its suppliers’ charging workers to obtain jobs. As Apple senior vice president of operations Jeff Williams writes in the report, “You’ll see that we consistently report suppliers’ violations of our standards. … Because of these audits, over $3.96 million was repaid to foreign contract workers for excessive recruitment fees charged by labor brokers. And nearly $900,000 was paid to workers for unpaid overtime.” Williams says that this is proof that the system is working.

I don’t agree, but not because there are violations. I suspect any multibillion dollar company with operations (or contractors) in as many places that Apple has will encounter similar, if underreported, problems.

No, the reason I don’t agree is because the same subcontractors keep getting caught for the same violations. That shows a decided lack of regard for their major customer’s brand and mandates.

I think Apple is taking the problems seriously, but its supply chain is not. And the chain has no real incentive to change. As such, until Apple starts firing suppliers, the problems of what amounts to indentured servitude at its contractors’ factories will continue unabated.

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Should Flextronics Be Broken Up?

The findings of a new study by Boston Consulting Group suggest that, over time, many tech companies are guilty of mission-creep, especially large ones.  And when that happens, those companies do not provide the shareholder value they could if they were leaner and more focused.

As part of its study, BCG analyzed total shareholder return, defined as the bottom-line return from capital gains and cash flow contribution. When it did so, it found little distinction between large-cap and small-cap companies:

“The clear takeaway is that regardless of company size, the more diverse the portfolio, the more difficult it is to generate high TSR—and the greater the set of management skills a company needs in order to handle that diversity. Companies must therefore be more deliberate and more explicit in rationalizing each element of their portfolio.”

BCG likens the strategy to the 3 R’s, in this case, Resize, Reform and Rejuvenate.  Marc Andreessen, the founder of Mosaic (later Netscape), put it this way: “If they’re more than 20 years old, then [companies will] probably benefit from being broken up, and many of them will probably be forced to break up if they don’t do it voluntarily.”

So for the EMS pseudo-conglomerates (Foxconn, Flextronics, Sanmina, etc.), what this means is there are arguments to be made — indeed, being made — that having bare boards, assemblies, design services, box build, ODM products, and a host of other products and services under a single umbrella is not an optimal  strategy.

There’s always been some debate over whether publicly traded EMS firms should be compared to other tech firms like Cisco and Microsoft or to traditional manufacturing companies (say, Caterpillar). It’s tough for a mid-size or larger contract manufacturer to attain repeated organic double-digit topline growth, and their margins are never going to be Wall Street pretty. Dumbing down the peer group makes sense.

But the bigger question being asked is whether their size is actually a hindrance. There must be a point at which that happens. Can the data analysis pinpoint that yet? And will market impatience make all of this moot?


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