Category Archives: Laying It Out

Off-grid thoughts from a burned-out designer turned editor.

10 Electronics Things to be Thankful for in 2010

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“Do they have 4th of July in Canada?”

The Thanksgiving holiday is upon those of us here in the United States. It’s been a bummer of a couple of years for a lot of the electronics world, but there’s still plenty to be thankful for — and I think it’s getting better. Well, “better” is a relative term, I guess. We at Screaming Circuits have gone from feeling the effects of the recession to being overwhelmed with work as people get back to designing stuff.

Here’s my recommendations on what to be thankful of this holiday season. Feel free to come up with your own list. I won’t look down on you if you don’t use my exact list.

#10: SIlicone. Because, while germanium is a semiconductor, silicon works much better. Germanium can’t stand the heat and had to get out of the fire.

#9: Flip chips. They’re so tiny and cute. And they have better thermal transfer properties than wire-bonded chips, not to mention improvements in inductance. And you can jam a whole lot more into the same space with little flip chips than you can with SOIC chips. Plus, if you run out of pepper, you can season your mashed potatoes with a bunch of spare flip chips. Just make sure they’re lead-free.

#8: HASL. Yes. It’s still around. And while it’s not the best solution for the aforementioned flip chips, it is one of the most robust, easiest to store, handle and use when dealing with larger geometries. It’s the way to go when hand soldering.

#7: ENIG and immersion silver. HASL may be my preference for hand soldering, but when using big BGAs or lots of small components, the bumpy surface of HASL can cause problems. That’s when a nice planar surface such as ENIG or immersion silver makes life a lot easier.

#6: Open source hardware. Open source has been helping out the software industry fore quite a while. It’s about time hardware folks benefited from the concept. In some ways it seems a bit exploitative of the designers, but as long as they are doing it voluntarily, I guess it’s okay. Open source hardware gave us the Arduino, which seems to have made microcontrollers a lot more accessible. It gave us DIY Drones, which seems to be proving that autonomy isn’t just for big-iron.

#5: mBed. This nice little ARM development board has taken a new approach to dramatically reducing the barriers to entry. With a complete online IDE and extremely easy startup and use, it will help a lot of people learn about advanced microcontrollers and will help a lot of people move from 8-bit up to the 32-bit ARM world. I don’t think you could make it any easier than this.

#4: FTDI. They made USB easy to implement on just about any design. Cool.

#3: The Beagleboard-xM. Speaking of open source hardware, the Beagleboard came about a few years ago as the first (as far as I could tell) seriously powerful open source hardware platform. It brought open source out of the hobby garage and into corporate America. The New xM has made the design even more powerful and indicates Ti’s commitment to the project.

#2: Quickturn PCB fab and assembly houses. Like Screaming Circuits for assembly and our buddies at Sunstone for the PCB fab, so you can get your prototypes built up a lot faster. Yes, I know this one is self-serving. But, you know, these guys pay my salary and I really believe in what we do here.

#1: Drum roll please…

#1: Caffeine. It helps us keep designing into the wee hours of the night. Then it helps us get back to designing early in the morning when we should be sleeping because we stayed up to late the night before. Caffeine is the fuel that powers our economic engine, so that’s my #1 thing to be thankful for this Thanksgiving. There is a part of me, however, that suspects that due to caffeine, we might just be doing this all wrong. Maybe we should, instead, try actually sleeping the proper number of hours per night. Just a thought.

Duane Benson
Wikipedia says caffeine is a natural pesticide. Hmmm…
Well, at least it’s natural.

http://blog.screamingcircuits.com/

Land Patterns – Equal and Not Equal

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I was recently asked a question about QFN package varieties. The questioner wanted to know if different package variants of 16 contact QFN packages, such as HUQFN, DHVQFN, SQFN and such, all shared the same footprint.

If they did, the CAD work would be much easier. There would be one land pattern to worry about and that would be that. Unfortunately, that is not that and in this case, that, in fact, that may never be that.

Many different varieties of QFN packages could use the same land pattern, but they don’t always do. Some will have the same pitch, but more distance between the outside contacts and the corner, thus a greater overall dimension. That can happen even with the same labeled variety of QFN package. Some will have different dimensions, differnt pitch, different pad sizes or different thermal pad sizes. Sorry. No easy answer here.

I popped on over to the NXP website, one of our Circuit Design ECOsystem partners, for some examples. NXP lists two 60 contact HUQFN part packages. One is 5 x 5 mm. The other is 6mm x 4mm. Same with the HVQFN. There is a 0.65 mm pitch, 4 x 4mm package and two 0.5 mm pitch, 3 x 3mm parts with a different overall package outline.

In general, generalzations aren’t going to work here. You’re going to have to go dig out that datasheet and quite possibly create a new land pattern.

Duane Benson
One pattern to rule them all and in the solder bind them

http://blog.screamingcircuits.com/

Need a Reference for the Reference

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Not long ago, I wrote a short post about non-standard use of reference designators. After doing that, I’ve been looking at some of my own microcontroller and motor driver boards with an eye for how close to standards I am.

All of the R’s, C’s, D’s and U’s are okay, but there are some differences. For example, the Eagle library I’ve been using calls crystals “X” instead of the more standard “Y.” I have seen crystals designated as “X”, “Y” and “Q.” LEDs seem to go by “LED” instead of “D” as indicated in the Wikipedia list. Headers go by “J”, “JP”, or “H.” Wikipedia says “J” is for a female jack connector, “JP” is for jumper, and it doesn’t list a “H.” My board has break away two-row male headers and keyed single-row male headers. Wikipedia does note that its list is a set of commonly used designators. Not necessarily standard.

We probably do have the specific standards document laying around here someplace, and if I were doing real work on a professional basis, I’d hunt it down and make sure I followed the actual standards. But I’m not doing real work with my controllers and drivers, so I just do the best I can. I wonder how often that happens everywhere. The standards books are “somewhere” but no one really knows where.

Duane Benson
Somwhere over the reflow…

http://blog.screamingcircuits.com/

Faster, Chug-a-Chug … Faster, Chug-a-Chug …

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Ever long for the days when you could lazily send out your files to get boards fabbed and a prototype assembled and then have a leisurely couple of weeks waiting for it all to completed and returned? Well, we’re not going to help you get back to that. In fact, we try to do the opposite. Let’s make everything speedier and speedier. I hope that’s okay.

Screaming Circuits’ PCB fab partner, Sunstone Circuits just added in a bit more to that end. Back in the old days, if you needed PCBs fabbed in 24 hours, you had to stick with two-layer boards. Not any more. They recently started offering four-layer PCBs fabbed in 24 hours in their PCBexpress quick-turn service. No rest for the weary. That’s especially cool if you’re having signal integrity problems and need to add in a ground and/or power plane layer.

Duane Benson
If by approaching the speed of light, time speeds up for you,
does time slow down for you as you approach “stopped”?

http://blog.screamingcircuits.com

AT Tiny is Tiny

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ATTINY44A-MMH I just spotted a note on Twitter, from SiliconFarmer, referring to the ATtiny44A coming in a 0.45 mm pitch QFN as well as a 0.5mm pitch MLF package. (In practice, an MLF is the same as a QFN, by the way.) (Just in case you actually care, we’re on Twitter at “pcbassembly.”)

I’ve run across a number of 0.4 mm BGA packaged parts, but this is the first sub-0.5 mm QFN I’ve seen. Interesting that they have two different sizes of QFN package, one at 4 x 4 mm and the other at 3 x 3mm. If you’re that tight on space, that little 7 square mm of extra open area can make a difference.

Screaming Circuits won’t care on the assembly floor. We do plenty of 0.4 mm parts so a 0.45 isn’t anything new. The most important thing to remember is to use the right footprint. It’s easy enough to accidentally use a QFP footprint when you have a QFN (like here). I could see it being even easier to swap for the wrong footprint with this part. Doing so would be bad, most certainly. You might get one or two contacts per side on the right footprint, but that’s pretty much as good as none.

Duane Benson
It’s like Ice-9. The same, only different.

http://blog.screamingcircuits.com/

Little Chippy Challenges

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And “chippy,” in this context, refers to chip caps and any other tiny two-connector components. When considering surface mount, most people think of the many-connector parts, like BGAs and QFNs as the challenging components. That’s mostly true. However, the little passives can be big bears too if not treated properly.

Two part tombstone You could have tombstoning problems. This can be caused by unequal sized pads, unequal sized traces going to the pads or inequality in copper plane in a different layer. A big part on one side can cause tombstoning too — the big part’s thermal mass may slow the solder paste melt on one side of the part, leading to tombstoning.H Skewed passive via in pad

Via-in-pad is still a problem too. Open vias can lead to unreliable connections, tombstoning or crooked  parts.

Soldermask tombstoning for blog Solder mask can cause problems too. Too thick a solder mask can prevent the part from reaching the solder and can cause tombstoning. Too think a solder mask can also interfere with outgassing in the reflow oven which can cause solder ball splatter. (A = okay, B = not okay).

Duane Benson
It just goes to show you…
It’s always something.

http://blog.screamingcircuits.com/

Electronics Shelf Life

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Do parts and PCBs have a shelf life? Well, yes and no. I have some 7400 series logic chips in DIP form that I bought back in 1980. Every now and then, I pull one out and put it into a proto board to test some circuit idea I’ve got. They still work thirty years later. I haven’t taken any special care in storage either. Some are stuck into anti-static foam. Some are not. All are sitting in a mini-parts bin without any moisture protection. I guess they do get a little shielding from light, but basically, they’re just hanging out. They’ve been, at various times, in the attic, in the basement, in the garage or in the house.

That may seem like good evidence refuting a shelf like for parts. And today’s parts are even more robustly Bent pins in strip designed to start with. Still though, if I use any of those parts, it’s generally in a proto board or a socket. Sometimes I have to straighten the leads a bit. A lot of things don’t matter so much at low temperatures, low speeds, low volumes and large geometries.

It’s different when you have fine pitch parts being picked up and placed by a robot and then run through a 10-zone reflow oven. Oxidation that doesn’t matter for a socketed prototype can interfere with the solder adhesion. Bent pins or missing BGA balls can prevent the part from fitting. Moisture absorbed over time can make the chip act like a popcorn kernel when in the reflow oven.

That’s not to say that you can’t use old parts for a prototype these days. Just give them a good inspection before sending them off for assembly. And, if they’re moisture sensitive parts or have been stored in high-humidity areas, consider having your assembly house bake them before assembly. The same goes for raw PCBs too. Overly moist PCBs can delaminate during reflow. Some PCB finishes such as immersion sliver and OSP can tarnish or degrade over time too.

Duane Benson
Archaeologists, we are not

http://blog.screamingcircuits.com/

Getting Ready for September

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I thought summer was supposed to be a time when things slowed down, a time when people take vacations and some time to relax. No such thing is happening here at UPMG.

For the last few months, we’ve been busy putting the program together for PCB West. This year we’ve pared the conference down to three days. One of the reasons is we’re moving the Design Excellence Certificate program to an online learning site that we call Printed Circuit University. PCU will launch right around the time of PCB West. As I’ve mentioned before, it will be a resource site for everyone involved in PCB design and will include a certificate program similar to the DEC we’ve held at the PCB Design Conferences for years. Stay tuned for more information on PCU.

During the three-day conference this year, we’ve scheduled almost 40 classes and presentations on subjects from the basics series by Susy Webb to Tom Hausser’s universal routing grid. In between we’re covering EMI, transmission lines, RF design, flex, embedded passives and many other subjects important to designers and engineers. We’ve even added a Tuesday track that covers subjects like counterfeit components and LED boards.

This year exhibit sales are slightly ahead of last year, including every major EDA company in the PCB market, as well as manufacturing and materials suppliers closely involved in the world of PCBs. Yes, these are companies that want your business, but they are also great resources for your design questions.
Registration is now open online, and you can get a look at the exhibitor list and complete program, including the “free” classes on Wednesday, by going to www.pcbwest.com.

Bottom line, PCB West may be only three days this year, but it is chock full of opportunities for everyone. Hope to see you there, and stay in touch.

p.

DesignCon Day 1: Light on ‘PCB’

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Today is Day One of the exhibits at DesignCon. I sat in a couple of classes yesterday by Bruce Archambeault and Lee Ritchey. Today’s itinerary is mostly meetings with exhibitors and a couple more classes. Unfortunately the program is not as deep in PCB subjects as I first thought. Out of just over 100 sessions in the program, I identified less than 10 that bore the “PCB Summit” logo. Kinda makes me wonder about the definition of PCB summit as DesignCon defines it.

Most of the classes are 40 minute sessions, so I should have plenty of time to visit with as many of the exhibitors as possible.

The only pre-breakfast news was from Intercept Technologies announcing a new “enhanced Interface” for their Pantheon layout software and SiSoft’s Quantum Channel Designer software for signal integrity. Intercept has been putting a lot of effort into updating and enhancing their signal integrity capabilities lately, and I’ve put them on the itinerary for later today.

More as the day progresses, so stay tuned.

Pete