Screaming Circuits: April 2010

ESC, Day 2

It's day two here at the ESC show. Yesterday was so busy, I didn't have time to write, walk around or do much more than talk and breathe.

Mbed etch Today has been pretty busy too, but I did get around a bit. I was able to stop by the ARM booth and take a look at what's going on with the mbed. They have it running an etch-a-sketch. Too funny.

I haven't had a chance to stop by the Texas Instruments booth yet to see what's new with the Beagleboard but I did at least get a passing glance as I sped by to a meeting. I think I saw Ethernet connectors on the board, so the new version must be up and I didnt sticker running.

One thing that made me laugh just came up here at the table I'm writing this blog post from. There's a little stack of stickers here. The stickers have a note on their back directing people to our Circuit Design ECOsystem partner, National Instruments; presumably for a survey. Made me laugh.

Duane Benson
Warning: There is no actual substance in this blog post

Castellated / Half-Vias, parts 2 - 255

I've written about the Castellated / half-via mounting system a couple of times in the past. Now I can't seem to avoid them. I'm seeing them everywhere. The GPS I recently wrote about, low noise amplifiers, POL power modules, frequency synthesizers, VCOs...

When did this become the package of the day? I haven't even seen what IPC has to say about it yet but these things are all over the place. Our engineers and assembly folks are cool with it. It's not that tough to build, fortunately. But, as I saw with the ublox part I wrote about, there are new design issues to contend with.

I can certainly see the advantages of the package. The half via can allow for a good solid fillet providing good mechanical connection. They're typically a pcb-type substrate so the coefficient of expansion and flex strengths should be similar to the underlying pcb. On the other hand, like with an LGA the low profile after soldering will tend to exacerbate any expansion or flex risks.

Duane Benson
Once in a dream
Far beyond these castellated walls...

ESC is near

The Embedded Systems Conference, Silicon Valley, is less than a week away and Screaming Circuits will be there in booth 827. I've been getting prepped all week (well, actually a lot longer than just all week) and that drives me a little crazy.

I ran across this diagram on XKCD that does a good job of explaining what value I get out of going to the ESC show. And, it conveniently points out the location of our booth.

Given that I'm posting this on my work blog, I feel compelled to include the warning that XKCD has on their website. "Warning: this comic occasionally contains strong language (which may be unsuitable for children), unusual humor (which may be unsuitable for adults), and advanced mathematics (which may be unsuitable for liberal-arts majors)" And the note that he licenses his work under a Creative Commons Attribution-NonCommercial 2.5 License.

I hope to see all of you there. Yes. ALL of you.

Duane Benson
No. This is not the algorithm either. Not even close.

Controlling the Uncontrolled

A nice coincidence. Recently, I wrote a bit about choosing a microcontroller and some issues that crop up when people not used to microcontroller design are tasked with automating systems.

My supposition is that, traditionally, most folks in the industry concentrate on designing and choosing microcontrollers and tool sets from the perspective of an expert in embedded design. However, the new world has a lot of people tasked with microcontroller hardware and software design that are not electronics or software engineers. Mechanical engineers are tasked with integrating electronic controls into their systems. Pure digital engineers are being tasked with adding analog sections into their designs. Hardware engineers are having to learn microcontroller firmware programming. That changes the ground rules.

Last week, I signed into a virtual conference on motor control (I started writing this post as I was listening to the virtual conference, but didn't get around to finishing it until today). I signed in late to start listening to the keynote address by John Hanks, of National Instruments and John was at that moment, discussing this very subject. As he described it, domain experts in such fields as solar, wind, and other areas are being asked to add additional automation into those systems. As domain experts, they may know more about their field than an EE or SE, but they likely have not been trained in the application of hardware, firmware and software development.

Interestingly, this group has a lot in common with the electronics hobbyist community. In both cases, the concepts and the tools are frequently quite new to them. In both cases, the budget for training and tools is frequently pretty minimal. In both cases, we have smart people who many not be trained in our field.

Those of us that create tools and offer services in this industry need to keep this trend in mind if we want to fully serve the new engineering audience.

Duane Benson
See us at ESC next week in booth 827

Let's Get Small

It never stops. Does it? It never stops, but it does seem to accelerate.

Mcro-csp When I fuddled with my first 7400 series logic chip a bazzilion years ago, it was a 0.1" pitch DIP chip. A few years after that, people were buying Macs with 0.1" pitch DIP 68000 processor chips. ten years after that, the new little PIC microcontrollers were largely 0.1" pitch DIP chips, but SOIC and .65mm pitch QFP packages were becoming more and more popular. Then came the 1mm and .8 and .65mm pitch BGAs. 0.5mm pitch BGAs became popular a few years ago as did the 0.5mm pitch QFNs. Last year, we started building the 0.4mm pitch BGA Ti OMAP processor with a 0.5mm pitch memory BGA on top of it in a package on package form factor.

If you spend any time reading about advanced packaging, you know that 0.3mm pitch CSP chips are near. I haven't heard of any passive form factor smaller than the 01005, but I guess that's where embedded passives will likely take hold. It makes my head swim sometimes.

Duane Benson

Who are your tool sets made for?

I've been thinking a lot lately about who's using microcontrollers and why these days. There's a lot at stake with this question. And, not just in terms of which microcontrollers are and will be the most popular. There's an element of the Toyota question in here too.

Traditionally, I suspect that electronics component manufactures, hardware EDA tool vendors and software tool vendors assume that their customers have been trained in EE, CS or similar discipline. I think to a point, that serves the industry well. But change is afoot in our industry. Because of a number of factors - too many to list here - virtually everything is getting some level of electronic control now. Years ago, that would have resulted in the hiring of a lot of electronics and software engineers. But not today.

The tried and true EE, accustomed to designing with logic and letting someone else worry about firmware, is now often tasked with designing in a microcontroller and then producing the firmware as well. Or a mechanical engineer is tasked with the same thing; something he or she never trained for. From what I can see, all sorts of technical folks that don't have programming experience, or any electronics design experience, are now being given that task. Schematic designers are now responsible for the board layout. Pure digital folks are often being required to add in a few RF sections.

What happens if all of the software tools (CAD packages, compilers & tool changes) are designed for well trained experts, but intelligent but untrained, in that field, folks need to use them?

When cars suddenly accelerate, MRI machines over-radiate or satellites fail, it's all good to look for tin whiskers, cosmic rays, manufacturing defects, software bugs and causes of that sort. But, what if the root cause is simply that someone trained and practiced in pure digital design was tasked with the "simple" function of adding in a few analog sensors and a tiny microcontroller. What if that designer had to learn a new discipline, a new tool set and still make budget and a tight deadline?

Maybe twenty years in digital design didn't prepare that designer for the quirkiness that goes with analog signals from sensors, or for the challenges involved in writing a small, but bullet proof SPI interface code. Maybe the designer is well used to determining spring strength and durability but now has to design a small electronic circuit to replace that spring. What does that do to quality and reliability? Food for thought.

Duane Benson
Thought is hungry today

Castellated / Half-Vias

Castellated Modules with castellated mounting holes are showing up more and more these days. I've also heard it called a "half-via" setup. Both seem to fit. The copper mounting pads on the bottom of the module's little PCB wrap up the side of the PCB with a half-via. Thus, the name "half-via." If looked at from the base, the edge does look a bit like the outline of the top of a castle wall, so that makes sense too.

UBlox paste layer Whatever. The name isn't that important. There are a few things that are important though, such as the land pattern and the solder deposition. I hadn't heard any special requirements for using this type of part until recently when I ran across a GPS receiver module from ublox. What they say is that you need more solder on the outside of the pad, than on the underside of the pad, so that it can properly wet up the half-via. That makes perfect sense. There are probably multiple ways of doing this, but you can see their take on it in the image here on the right that came from their data sheet.

Obviously, follow the datasheet that comes with your specific part, but if you don't have any official guidance and can't get word from your part manufacturer's applications engineers, you might take a hint from this method. The copper land is just a standard rectangle, as is the solder mask. The paste layer, however, is not. It's wider toward the outside of the part. This will help create a proper fillet up the via while reducing the chance of solder balls and other messy things that can happen when you have too much solder under a part.

Duane Benson

Crooked Components

I was looking at two different PCBs recently; one assembled here at Screaming Circuits, and one, a PC graphics card assembled someplace else in the world. In both cases, a crooked component caught my eye. The graphics card, at least, would have done a passable job of meeting IPC-A-610 Class II, but in both cases, the offset was enough to inspire me to take a closer look and write this blog post.

On the graphics card, the particular component was an SMT inductor. I've been having some issues with the card and when I had it out of the PC, I saw that inductor. With further examination, I found a lot of other crooked components. My off-the-cuff conclusion was that the manufacturing workmanship was poor, therefore I shouldn't be surprised that the card was having issues, and perhaps I should look for a different brand for my next purchase. Again, everything would likely have met IPC Class II, but perception is close enough to reality and that manufacturer has probably lost a customer.

SD land with hole In the case here at Screaming Circuits, only the one component, an SMT SD card socket, was crooked. In addition to the signal pads, this socket has four large SMT pads, one on each corner, for mechanical connection to the PCB. One of those four pads on this PCB has a big hole in it. Not just a little 10 mil via in the pad, but a either a really, big via or a bolt hole. The unequal surface tension in the solder, caused by that pad being cut in half, caused the connector to twist a bit.

Yes, in a prototype world, we made it work, but it caught our attention here and if such a thing went into final manufacturing, it might very well catch a customer's attention and elicit the same response I had to the graphics card. It will work okay and would probably stay secure on the board (maybe), but it's not good practice and it looks wrong and wrong looks can cause customers to go elsewhere. Yes, function is key, but if form chases customers away, then function never gets a chance to matter.

Duane Benson
We'll keep the robots in line
You keep the PCB in line


Screaming Circuits is seeing more and more components in short supply or on allocation these days. A while back, we took a survey of our customers and found that on average, an engineer would spend about 16 hours sourcing parts for a prototype design.

Schottky top My question is has that changed? There are a few chip companies with a lot of parts in short supply, but what I hear the most about is the passive components. If you've designed a very specific power or radio chip, for example, I can see how a twelve week lead time can be a very big issue. But if it's just a 47pf, 6volt cap, a resistor or diode, is it really that difficult to find a sub quickly?

How much of an issue is parts availability today - really? Is it something that has a lot of visibility and little impact? Or is it something where the visibility and the impact are both pretty big? How much of a hassle and time sink is it for you now?

Duane Benson
I'll trade you a pair of .022 for one .047

Full Circle - Total Quality Management

A thought occurred to me over the weekend as I was pursuing through some of my recent posts and comments.

Back in the late 80's and early 90's, Total Quality Management with such phrases as "Cross-functional team" was all the rage. Essentially, what that meant was that when time to start developing a product, folks from throughout the process would meet; marketing, sales, engineering, mechanical, purchasing, manufacturing, shipping and any other functional groups would send representatives to the product team. That team would meet throughout the development process to ensure that the product was designable, buildable and sellable. It worked.

But... What happens when three quarters of the process is outsourced to three or four different organizations throughout the world? Unless you are very diligent, that quality process breaks down. Then when you remove some of the experts (such as layout specialists), the process can breakdown further. That's where we are now. Perhaps we need to go back in time again and figure out how to get everyone talking and passing data back and forth again.

Duane Benson
Yes - I successfully resisted the temptation to say "we need to go back to the future..."

« March 2010 | Main | May 2010 »