Mysteries of Engineering

I (and many, many of us, presumably) have been reading more about all of the Toyota woes and the to-date unanswerable questions. Still, so much of the material written about the issues seems to be coming from the untrained. Certainly, human behavior suggests that some of these problems could be the result of operator error. But, I'm not an expert in human behavior, so I can't really say. And, certainly, problems do crop up in complex machinery, like cars. I don't know if that supposition falls within my area of expertise, but a few decades of operating motor vehicles gives me some personal empirical data on that one.

The area that does bother me the most is probably those that speculate that since the problem hasn't been found, it doesn't exist. This is an area where I can claim some level of expertise as well as plenty of personal empirical data.

It is possible to spend uncountable hours testing various possible conditions and still never uncover the one scenario that will cause a systems failure in the hands of the general public. Many years ago, I worked for a company that designed, built and sold projectors. In that day, these were big things with short-life, very hot, incandescent lamps. We thought that we had done a very through job of testing under various conditions and had been selling the product for a little while when reports started filing in of bulbs exploding. It wasn't just a simple break. The bulbs were exploding with such force that the bulb area was filled with a fine grained, razor sharp glass dust. Nasty.

ExplosionDuring a weekend burn in session with a couple dozen projectors, including some returned from the field, the engineer monitoring the process thought he heard a gunshot and dove to the floor. It wasn't a gunshot, but it was the first clue in a long investigative process that did end up finding the problem. It seemed that if a bulb was too deeply seated in the socket by a couple of millimeters, the reflection of the filament in the mirror would exactly line up with the actual filament, causing it to melt and arc. The arc would run in one direction, down the filament leg to the base and stop.

One filament leg had a few coils of small diameter tungsten wire wrapped around it. The other leg did not. Depending on the orientation of the supposedly non-polar bulb, the arc would either run down the leg with no coil or the leg with the coil.

If the arc ran down the leg without the coil, nothing happened other then the bulb needed to be replaced. If it ran down the leg with the coil, that small amount of additional vaporized tungsten increased the internal pressure sufficiently to explode the quartz bulb in a very catastrophic manner. Okay, now that's weird and obscure. Technically, you could call it operator error. If the customer had just inserted the replacement bulb the exact same way we inserted the bulbs during production, the problem would never have happened. But, realistically, it was a design flaw that set the customers up for a failure.

Duane Benson
Duck and cover

Thermal Mass Follow Up

RoHS has been with the electronics manufacturing world for quite a while now but there is still a lot of issues and uncertainty associated with it. As I wrote not long ago, even parts that are supposedly compliant can in some cases not cut it.

Taylor asked in the comments section of that post: "Have you noticed any pattern in capacitor manufacturersClose caps 3 exhibiting this problem? How can make sure to spec a capacitor that is more robust?"

Close caps 1 I can't say that I've seen a real consistent pattern with components from different manufacturers here. It's a case where the design engineer may have to compare the exact thermal specs from different components' data sheets and throw in a good measure of intuition and judgment as well.

In some cases, you might be able to replace a couple of capacitors with a single of a larger value, but in general, if you need multiples, combining them won't do. There are certainly good reasons to parallel up capacitors. You may need a few of different values to cover different frequencies. You may have a clearance issue and not have enough height for a taller cap. Or you may need to keep the ESR (Effective Series Resistance) down. Whatever the reason, if you need a number of caps close together, and they are big SMT electrolytics, you could be setting yourself up for this problem.

Close caps 2 Image A illustrates the issue found in that earlier post. The thermal mass of all of those big metal can caps can slow the solder melt. The most vulnerable pads are the two inside pads for C3 and C4. Keep the heat up long enough to fully melt the solder on all pads and you may destroy the caps, or other components.

You could just spread the two rows apart a bit like in illustration B. This might be enough to allow all pads to solder well or, if nothing else, it would give you enough room to touch up with a soldering iron.

Probably the most common solution though is to take the approach used in illustration C. Just put all the caps in a row so none of the pads are vulnerable.

If you need a compact layout like A, you'll just need to spend some extra time with datasheets to find a specific cap with a bit of extra RoHS temperature margin. Look at the maximum solder temp, the maximum dwell time and the profile curve if available. Don't forget to check your other components too to make sure that the extra reflow time wont harm them either.

Duane Benson

Toyota is as Toyota does

Everyone else seems to be writing about Toyota sudden acceleration problems, so I should probably do that too.

Or should I? Personally, I have absolutely no solid information about what's going on with Toyota cars. There's an awful lot written, much of if by people that also don't have any real information on the subject. Here's what I do know though:

  • Some people (some with actual knowledge and some without) are speculating that electronics might have something to do with the problems.

That's about all I know relative to the specific concerns. On the soft side, I do know that people tend to pick on the big guy. Funny how none of this was big news until Toyota became the #1 car maker in the world. Coincidence? Maybe. Maybe not. I also know that in any system there are gobs of places where LED via-in-padissues can lead to failures. Of course, to counter that, I know that good, well thought out design - both in the hardware and the software, can produce a quality product that will keep working. In summary, I really don'tSilk on pad know anything about the Toyota issues.

However, any time some sort of actual or potential technical problem makes big news, it's not a bad idea for those that design and build things to take a step back and evaluate our design practices. I've got software in my past, so I'd have to suggest a good solid code review, if you don't already do one, but today, I'm talking about hardware so I'll sample just a few things to double check.

  • Those pesky land patterns: Does the land pattern fit the part? Will the copper area and stencil opening allow for a good solid IPC-passing solder joint? It's so common (as you well know if you read here regularly) to re use or create new CAD part foot prints. Make sure the foot print, stencil, mask and silk layers fit properly.
  • Vias in pads: Plug them and plate over them when using small parts. If the solder surface is big enough, like with a power component, you might be able to just cap them, but don't leave the vias open. In some cases, you may be able to leave very tiny vias open on thermal pads, but it's best never to.
  • Thermal mass: This is important both for operation and for assembly. If you've got components that sink and/or generate lots of heat, make sure there is enough air flow to cool them during operation and make sure that the assembly house can build it. Put a couple of high thermal mass parts too close together and an otherwise perfect PCB assembly may end up with some cold solder joints or damaged components that later come back to bite you or your customers.

There are lot's of other things to check out too, but those three are just some of the more common traps to keep tabs on.

Duane Benson
I don't have a Toy Yoda. If I did, I'd sell in on eBay.

Is Geek Cool?

When I was young, "Geek" was not cool. Neither was "Nerd". Working on cars was cool as was logging and shooting Bambi's uncles with high powered rifles, at least where I came from things were that way. On the other hand, every little town had a Radio Shack where you could buy tubes, transistors, ICs and other assorted electronic components. You don't see that so much anymore. Grocery stores sold publications like Byte Magazine, 101 Electronics Projects and Radio Electronics. Those magazines were about building things. People who read and wrote those and others like them created an industry in their garages, basements and bedrooms. They started a new Industrial Revolution.

Still, back then, tech folks were more likely thought of as mad monks and strange people like Eddie Deezen as "Mr Potato head" (Malvin) in the 1983 movie War Games. You didn't want to be one. I like to think that attitudes have changed over the years, and I think the signs are there.

The FIRST Lego league with its robotics tournaments has created a legitimate "sports like" atmosphere for geek-types in school. 50,000 plus Arduinos being sold shows that the electronics hobbyist world is moving again like it did in the 80's. The maker and bender communities illustrated by Hackaday, Makezine and supported by companies like Adafruit and SparkFun show that creating with chips is as alive as it was in the late 70's and 80's. TV shows like Mythbusters, Jimmy Neutron and Prototype This have glorified the geek.

And why do we care? Because the more engineers we build out of the masses, the better we can design and build our economy. The more mainstream and acceptably technology is, the more educators will work to encourage and foster the environment and attitudes that allowed Apple, Dell, Google and SparkFun to thrive. We need that. We need robotics competitions to be as socially acceptable as football games.

Duane Benson
The rooms were so much colder then

The Next Industrial Revolution - Is Happening In 1910

Matt, our product manager, sent me a couple of interesting links about the next Industrial Revolution. The first was an article in Wired Magazine by Chris Anderson. The second was a rebuttal in Gizmodo by Joel Johnson. Both had some interesting points. Both, as far as my thoughts go, have some truth and both have some silliness, again as far as my thoughts go.

RCA12ax7_sq_arms Regarding the idea that what is going is something new and revolutionary, well, maybe the products are new, but the process really isn't, but for a few specific details. A while back, the country was coming off of an economic down turn and a wholesale group of young folk with tools at hand built an industry in garages and barns. That was the auto industry.

All of those farm kids grew up around machinery. They all had the tools at hand and the knowledge to use them. Communications (teletype, telephone, newspapers) was changing the way information flowed around the country and world. Transportation (railroad and the autos/trucks that they were building) was in revolution and changing the accessibility of new markets.

Car companies were coming and going all over the place. Sound familiar? Then there was consolidation, conformity, near-monopoly, bloatware and then crash. Yeah, and the same thing started with electronics and computing back in the 60's, 70's and 80's. It's happening again now too. Big surprise. It happens whenever there is a convergence of the cycles of low-barrier to entry (good, cheap tools), emerging technology and bright young folks with time on their hands.

I see some of what Chris is talking about in our electronics manufacturing customers. I just have a bit of a different take on it. First, rather than seeing this all as new, I kind of feel like "here it goes again." Second, I think what he misses is the concept of scale. On certain scales, what he says is very true and very workable. However, companies that spend a few years developing their products would like to eat food and send their kids to college, so they need to earn money for that intellectual property they have developed. That being the case, they still need a place to build their things, but a place that wont steal that intellectual property and deny the company's kids their college education and food.

There's a place for the model Chris is describing. There's also a place for megalithic industry producing gajillions. And there's a place for companies like Screaming Circuits that cost more than open source but focus on making life easy for an engineer and can build prototypes or flexible low to mid volume manufacturing without the hassle of big industry or the risk of losing a livelihood to people with a very liberal interpretation of who owns what. (see #1101 in this post)

Duane Benson
Danger Will Robinson!

LED Lighting Assembly

When I first attached a 280 ohm resistor in series with a 5mm red LED, the word on the street was that LEDs were low power, forever-lasting devices that would just about completely replace incandescent bulbs for simple binary indicators. LEDs spent a brief period as the numerical display device of choice too, until supplanted by the LCD. Regardless, the bottom line was that LEDs were really easy to work with. Just put that resistor in series - usually, you didn't even need to do the ohms law calculation - rules of thumb were good enough.

Lots of LEDs

Well, for simple binary indicators, that still holds true, but the big noise in LEDs these days has little to do with binary indicators. It's in illumination, and in illumination, all the rules are different.

800px-2007-07-24_High-power_light_emiting_diodes_(Luxeon,_Lumiled) High-brightness LED illuminations devices are some pretty seriously engineered systems. Most have current regulated power supplies. Portable applications often have buck/boost supplies allowing for constant brightness over the life of the battery. And most have serious thermal design work put into them as well. LED lighting designers not only need to worry about all those power supply issues, but also about heat sinking and exotic design techniques such as metal core PCBs and heavy copper. Though it's just an LED, the layout and assembly issues are far from trivial.

Duane Benson
Wear shades 'cause when you're cool, the sun always shines.
Or maybe someone's just trying to blind you with a bright LED flashlight because your ego got too big.

Pitch Switching

I recently started reading the magazine Chip Scale Review. It's a different take on things than I'm used to. Most of what I read for work is in the engineering and assembly realm, but this one goes back to the component packaging. I think it will be a good one in terms of keeping up on what sorts of things we'll need to be assembling in the future.

So far, I haven't seen anything really scary in it. There is talk of .3mm pitch BGAs, but those aren't totally new. I'm not sure if we've done any .3mm pitch before, but we've been doing .5mm for years and have done plenty of .4mm pitch as well, even in package-on-package (POP) forms.

Pitch switching adapter Speaking of really fine pitch BGAs and CSP type things, one topic I found interesting has to do with pitch switching adapters. It's basically a small PCB platform that has an underside footprint of a 1mm or 1.27mm pitch BGA and a land pattern on top for a fine pitch BGA. It has solder balls on the bottom, so once sandwiched together, it's treated just like a big BGA for assembly purposes. [Credit where credit is due: The image I'm using came from the Aries Electric web site.]

Such a part can negate the need to re-spin the PCB if your big part is updated and replaced in a new fine-pitch form-factor. (Although, personally, I can only imagine that if the chip is rev'ed, there will be some other change that has to be made to go along with it). The theory is, that if you've got a really expensive design, this might be a viable option allowing you to upgrade without a relayout.

Certainly though, at the very least, this could allow you use some newer fancy chips without having to resort to filled micro vias and tiny trace & space advanced (expensive) pcbs. Could be quite handy and same some money.

Duane Benson
Platform shoes are back!

Newark Electronics and Eagle CAD - Interesting

So, I just read that Newark purchased Cadsoft Eagle. I guess it's probably old news to everyone but me. The press release about it that Newark posted on their website Element 14, has a date of August 13. I find this purchase to be an interesting development and I don't quite know what it means, or if it means anything.

I guess partnering is becoming a trend. Certainly, we're involved in some good partnerships (Sunstone, Digikey, NXP, National Instruments) and Sunstone's PCB123 connects up with DigiKey parts. It does make sense. The engineer's job has just gotten more difficult with this recession and the ensuing reduction in support staff. That's pretty much what our ECOsystem partnership is all about - taking the disparate tasks involved in getting a prototype built up and reducing the steps and complexity involved in the process.

The Eagle / Newark deal does have me very curious. For one, I hope the CadSoft folks got a good deal. Their product has done a lot toward lowering the barriers to electronics design and they deserve a lot for that. The big questions are for the future. Will Eagle remain as accessible as it is? Will Newark throw a lot of resources into it and keep it moving forward? Will it get good attention or will it be treated as an impulse buy and not be given focus or direction? Hmmm...

Duane Benson
What about Element 32?

My mbed Is Up

I wrote about the new mbed development board a while back and mine just arrived over the holiday weekend. I have to say, true to it's promise, It was the easiest piece of development hardware that I've ever brought up:

  1. Take it out of the shipping box
  2. Plug in the USB cable to the board and my computer
  3. Wait a minute for it to be recognized and open up like a USB thumb drive
  4. Double click on the web shortcut in the drive
  5. Register
  6. Click the Compiler link
  7. Pull up a code sample and modify it a bit (I didn't need to modify it, but I did anyway)
  8. Click the compile button
  9. Save it to the mbed as though it were a USB thumb drive
  10. Press the reset button on the mbed board

That's ten steps, but it's only ten steps. There was nothing else to do. Nothing. The longest step was number seven which took me about two minutes. I programmed a "Knight Rider" sweeper with the four on-board LEDs. I made one of those for my Jack-o-lantern back at Halloween, so it was the first test program that popped into my head.

I built the Jack-o-lantern sweeper with eight LEDs and an 8 bit PIC16F819. The PIC I used came in an 18 pin thru-hole DIP package, costing $3.22 at Digi-Key, and I hand soldered it all on an old perf board. It runs at 20MHz, has 16 GPIO, 3.5K program code space, 256 bytes of FLASH and 256 bytes of RAM.

Mbed pinout The 32 bit NXP LPC1764 runs at 100MHz in a 100 pin LQFP and costs $8.70 in quantity of one at Digi-Key. (The dev board, of course, costs more then that) It has 512K of program FLASH and 64K of RAM. The dev board can have up to 25 GPIO (the chip can have up to 70 GPIO with your hardware) along with the standard assortment of peripherals that can be configured, including six hardware PWM channels. The mbed dev board is like a breakout board configured as a 40 pin 0.1" DIP so it will be easy to prototype with.

The processor, being a fine-pitch package really isn't hand-solderable like the PIC except for by the most adventurous of folks, but that's where Screaming Circuits comes in. Why wait for your custom hardware before starting on the software. Get one of these mbed dev boards to work on your software while the EE folks are designing the custom hardware. Then, when they're done, we'll assemble up the prototypes and you can integrate it all together. Take some time out of your development schedule that way.

I've wanted to try out an ARM processor for quite a while, but prior to this, haven't found the right way to do so while keeping within the limits of my time availability and skill set, but this looks like it could very well do the job.

Duane Benson
Robots rule!


More On Allocation

Not long ago, I wrote a bit about allocation and parts substitution issues. Once again, I can't stress enough that if you're in a hurry, you need to be prepared with some subs ahead of time. Especially with the don't-think-about-them passives. Right now, that's where the biggest issues seem to be. IC's are starting to show supply problems too, but the passives are the big hitter at the moment.

BOM line items Something else to be wary about in times like this is the prospect of counterfeit parts. Unfortunately, when supply gets tight, that's when the opportunists come out of the woodwork. Legitimate suppliers like DigiKey do a pretty good job of keeping their parts real, but unknown suppliers need to be looked at with caution. We do use some brokers here, but we qualify them carefully and keep watch on how they are doing things.

If you really, really need a specific component that has 12-week lead times everywhere and some unknown Internet supplier can get you some now, be careful. It may be a lifesaver, but be prepared to test the part to make sure it's really what you are expecting. And, if you just can't get that perfect part, maybe a slight design change is the only way to get some of that 12 weeks back.

Duane Benson
Drivin' over Kanan, solderin' on my soul
There's people out there turnin' duds into gold