Oh MSOP, My MSOP

In the land of protorypes, sometimes "close enough" is good enough. That can save money on PC boards and assembly when a particular package version of your part is out of stock. But, it's not universal. Sometimes you can't go that way.

I've got an MCP78338 Li Poly charger chip. It comes in 10-DFN and 10-MSOP packages. I originally used the MSOP version on my first PCB pass. Everthing worked just fine, so I re-layed out the board to be about half the area. That meant that wherever possible, passives went from 0603 to 0402 and chips went from whatever to QFN/DFN pacakges.

Unfortunately, the DFN package Li Poly charger seems to be out of stock with long lead times. That got me looking at my options. Option 1, would of course be to just wait. Option 2 would be to re-lay out the board for the MSOP part in that space. Option three is to use the "we'll make it fit" mantra. There are no gurantees at this point, but sometimes it's worth a try.

But... Twas not to be. If you look at the second image, you can see that the footprint of the MSOP part leads is wider than the land pads for the DFN. I suppose there are still a few really messy and potentially expensive options You could solder a small wire on to the pads, sticking out from the pads, effectively making them big enough to accomodate the chip. Very ugly, but might work. Probably too spendy though.

Duane Benson
Carpe DFN

QFN Solder Paste Layer

I've got the fab order placed with Sunstone.com for my next demo project. The little board is represented here at pretty close to actual size on screen - provided you have a 22" monitor set at 1680 pixel horizontal resolution. Give that, you might want to click on it to pop up a bigger representation of it. That makes it about 4 X life size.

When you do that, take note of the QFN / DFN parts: The processor in the middle, the LiPoly battery charger right between the upper two mounting holes and the RS232 driver in the lower left. I've followed my paste layer advice and segmented the paste stencil layer to reduce the chance for float or major voids.

I found a footprint in the library for the big processor in the middle. I just had to modify the paste layer, as shown here. I made the footprint for the charger and RS232 chips from scratch. Neither had anything close enough in the library.

The DFN has a slightly different approach to segmenting the stencil layer. Little squares like I used on the other two chips work just as well, but this is effective as well.

Another thing to take note of is the markation on the LEDs. The original footprint for the 0402 LEDs does have a polarity mark, but it's one of the types that can easily be misinterpreted or can be difficult to see. The diode symbol put down in silk screen removes any possibility of ambiguity.

Duane Benson
I'm happy I live in a split level head.

 

Showing Off at ESC 2012

Yes, we show off sometimes. We show off and get self congratulatory and self promotional. 'Cause that's what tradeshows are all about. Well, they're about that, but they're also about meeting and listening to people and other good things. In any case, we are proud of what we do (otherwise I wouldn't be doing it) so we go to tradeshows and show off.

In March, we're going to the Embedded Systems Conference in San Jose, California. We'll be in booth number 1437 (map here). Show hours are as follows:

Tuesday, March 27 - 11:30am - 7:00pm
Wednesday, March 28 - 11:30am – 5:30pm
Thursday, March 29 - 10:30am – 3:00pm

We always bring some samples of our work for people to hold on to. We've brought the two Beagleboards that we assembled and a few other pieces of our handiwork. It's cool to pick them up and hold them, but with parts so tiny, it's not easy to really see what you need to see from an assembler - the solder joints. So this year, we're bringing some big monitors and a USB microscope. I've got my eye on this one from Adafruit. As of this writing, it's out of stock, and I'm anxiously waiting for notice that it's back in stock.

Duane Benson
Let's get small

Particle Update

I've been ignoring my Geiger counter for a while now, but I picked it back up and made some progress again. For some reason, I just wasn't getting the 555 based HV power supply to generate a high enough voltage. In frustration, I bypassed the 555 and fed a PWM signal in from a microcontroller board that I have laying around.

That fixed the problem. I still don't know why I wasn't able to the the 555 doing what it was supposed to do. I'll have to spend some more time on that some other day, but for now, I've prototyped it out and I'm happily detecting particles. I whipped out the new layout and will send off to Sunstone.com com for another set of PCBs.

I've also replaced the Atmel chip with a PIC. I don't have anything against Atmel. I'm just more familiar with PICs. Once I've built a few of these, I'll change to really small packages - QFNs or BGAs for the chips - to make the board a little more fitting with our assembly capabilities. The SOIC chips are fine, but our machines don't even come close to breaking a sweat with things that big.

Duane Benson
We treat agoraphobia for PC boards

Who Are You?

A lot of events are preceded with a "meet and greet" session. It gives you something to do for an hour or so before the real activity takes place. I'm not much of a schmoozer myself, but if the crowd is right, there is value in the activity. It's good to get to know folks with similar interests or vocations.

On the Internet, Facebook is kind of known as the place for that sort of thing. The problem with it though is the low signal to noise ratio. Too much drivel to sort through to find the valuable nuggets. But don't despair. All is not lost. Over at EEWeb, they have something pretty close in their "Featured Engineer" series. As of this writing, they have well North of a hundred profiles. Peruse through and get to know some or the people making things happen in the world these days.

If you look close, you can find yours truly in the list. And the first person to name the science fiction movie I'm thinking about gets a free Screaming Circuits polo shirt. The first person who can correctly identify the lighthouse gets one too. (the lighthouse is small in the photo, but if you've been there, you'll recognise the area) Only in the U.S. though. Sorry, but customs gets me down so I'll only ship to a U.S. address. It might not be the same shirt I'm wearing, but close.

Duane Benson
In life I was your partner, Jacob Marley.

Is your BOM a Smart BOM?

Please be aware that there is no "B" at the end of these BOMs. Still, without the "B", you can have a smart BOM or a dumb BOM. It is important to note, however, that a dumb BOM may not be a bad thing. It just depends on what you want to do with it.

No matter what you're doing, there are a few necessities. Let's start at the very minimum, for someone designing something to be self-built from mostly already owned parts; maybe just a few from a dealer.

Reference designator: R1, R2, R3, C1, C2, U1... You have to have this information.

Quantity is important so know know how many to pull. Although, with a small garage-built project, you can probably just as easily count how many you need for a given value. And what about the value? Actually, the value isn't always all that necessary if you have the correct part number information. A line item number is hand for big bills to keep things straight.

This is actually too basic and kind of pointless, so I'm going to jump ahead. Take an assembly house like Screaming Circuits. Screaming Circuits will either build your boards from your kit of parts or purchase them from your BOM (or a combination thereof).

Once you have the item number, quantity and reference designator, you need to tell your assembler or purchaser what it is. If you already have the parts kit, just add in the manufacturer's part number and a description / value. That should do it. Some assemblers, like Screaming Circuits, will take part numbers from a distributor in place of or in addition to the manufacturer's part number(e.g. Element14, Digikey...)

If the assembly house is going to buy the parts, then add in the manufacturer and double check that the part numbers are accurate with all suffixes and things of that sort. The distributor part number can be added, but when the assembler is going to build the boards, you really should include the manufacturer and manufacturer's part number to cover all basis.

That's cool, but your circumstances might require just a little more. You might need to list an approved substitute or two for parts that come in and out of stock frequently. You could also list multiple distributor part numbers for the same specific component, again, in case of lead-time or stock issues.

Sometimes I get myself into a bit of trouble by not specifying some part values at design time. I might just throw in things like bypass caps, RS232 driver charge pump caps or LED current limiting resistors assuming that I just know what the value is. It's not a big issue, but it would probably be less work to just do it at the start.

Duane Benson
What the Bureau of Meteorology has to do with your parts kit, I'm not sure.

 

Let's Get Small - 0.3mm pitch BGA

I recently got an email from Practical Components about their new 0.3mm pitch evaluation board and dummy 0.3mm pitch BGA. Now, we've been assembling 0.5mm and 0.4mm pitch BGAs for years. Those sizes are kind of not really anything special anymore. We've even been putting together POP (package on package) for a couple of years. But we've yet to see anything smaller.

Just looking at the numbers, 0.3 may not look all that much smaller than 0.4, but that's 25% down. Thinking of it in those terms makes it much more intimidating. I haven't found the pad dimensions yet, but just using rough estimates, a 3 mil trace would have about 1.5 mils on either side for a between the pads trace. That's getting pretty dangerous. Likely, you'd have to do every thing with filled and plated-over vias in the pads. (NO OPEN VIAS! Not one. Don't do it.)

I can see a lot of good future use for this size in miniature devices; more processing power in hearing aids and embedded medical devices, for a start. I don't know how necessary 0.3mm pitch will be for phones. They seem to have stabilized in size and the trend is more toward system in chip than it is toward more shrinking. Regardless, I would expect that in a year, we'll be seeing mainstream parts in this form factor.

Duane Benson
Go ask Alice
I think she'll know
How to run your escape routing

Top Ten Things To Do In 2012

Unless you've managed to live off the grid for the last five years, you know that the Mayan calendar has predicted the end of the world on December 21, 2012. Ignoring all conventional wisdom, centuries of scientific knowledge and the fact that the Mayan community doesn't even believe it, I feel compelled to list key electronics things that everyone should see or do in this last year before the end of the world. Because, you know, just in case...

Here are the top ten things to look into or do in 2012 before the end of the world on December 21, 2012:

0b0000.0000: Build something open source. It's amazing what is available. Back in the heyday of hobby electronics, it was easy to find projects in magazines such as "Popular Electronics." You could get kits from Heathkit or RadioShack. But, for the most part, all of those things went away. With Open Source, you can build an almost unlimited variety of gadgets. What's more, you can taylor your build to your experience level. If you want to do it all, just get the files, fab your boards, buy your parts and solder it up. If you're less ambitious, buy a complete kit. If you're even more ambitious, mod the design and post it up for the community.

0b0000.0001: While you're out fiddling with Open Source, get ahold of a Beaglebone. It's Ti's second take on open source hardware. The original Beaglebard was and is a great way to get to know their OMAP processors, both in therms of programming it and in terms of designing a PCB for it. The Beaglebone is an easier to use, easier to expand, but not quite as powerful adjunct to the Beagleboard.

0b0000.0010: Try out some new CAD software. Sunstone released PCB123 version 4 in 2011 and Element14 released EagleCAD version 6. Check them out and see if they do what you need. Both are good economical ways to get into circuit design and layout. PCB123 doesn't cost anything initially. It sends your boards through Sunstone and they earn their rent that way. Eagle has a tiered pricing model, starting at a small non-commercial version for free and stepping up to a full-feature professional system.

0b0000.0011: Try out some newer technology. I'f you've always been intimidated by QFN or micro BGA packages, go ahead and give it a try. They're more difficult at first, but once you've got the tricks down, you get access to a slew of new components that only come out in those form factors. Check out some guidelines on QFN use.

0b0000.0100: Look at space pictures. There are a number of probes up running around our solar system these days, and one on the verge of leaving it. Hop on over the nasa.gov or space.com and see what's going on. There's a probe orbiting an asteroid, new ones off to Jupiter and Mars, one orbiting Mercury, some new space telescopes and more. There's just a lot going on out there right now. You can even leave your computer, go outside and look up at the sky for real.

0b0000.0101: Try and make something really, really small. For my part, I'm taking a little two-motor robot brain I've built and an trying to see just how small I can make it. You have to think differently when size is a prime consideration. Factors that didn't matter much suddenly become design critical. It might be an opportunity to freshen your brain up a bit (although, if the world is ending on 12-21-12, having a fresh brain may not be all that important).

0b0000.0110: Go back in time. Get a 2N2222 or 2N3907, or both. See if you remember how to build basic common base, common emitter and common collector amplifiers. No. Don't go to Wikipedia. Try to do it from memory. I'm sure you built all of them waaaay back in your school days. Next try to build some basic logic gates with transistors. After you've done that, see if you can build up a RSIC processor and a 512 Mbyte RAM block using only discrete transistors and passives. As your final assignment, use the computer system you built to calculate the first 100,000 prime numbers.

0b0000.0111: Take your most recent resume and replace all of the letters, spaces, tabs and line ends with their hex values. Submit it in that form for your dream job. Then sit back and wait for the hiring manager to bow down to your superior skills. Since the world is ending, it really won't matter that the first person to see the resume thought it was gibberish and round-filed it.

0b0000.1000: Introduce your kids (if you have them) to robots. Get them started down the technical path early; both boys and girls. And, if you have daughters, make sure they don't get discouraged by peer pressure or whatever pressure. If they are interested in a technical career, don't let the world around them pressure them out of it. If you don't have kids, build some robots yourself and introduce your pets to them. See who ends up chasing whom around the house.

0b0000.1001: Finally, ignore all of this. Come on. Really? The Mayans knew when the world would end? Even I don't know that. Although, there was that John Cusack movie. And I've read about it on the Internet and everyone knows that if you read it on the Internet, it must be true...

Duane Benson
See you all on the other side

Screaming Circuits and Element14

Screaming Circuits has entered into a partnership with electronics distributor Newark/element14 to offer PCB assembly services through its online engineering community, the knode.

As support staff, schedules and components shrink, design workload stays the same or increases. The Knode on element14 is an intelligent online search and knowledge tool that helps to quickly find the right solutions for all phases of the design cycle. It saves time by centralizing unbiased information, components, advice and services in one common location.

With this agreement, Screaming Circuits’ pcb assembly services are now available via the Knode. This provides a one-stop shopping experience that can deliver machine assembled prototypes in as little as 24 hours, in quantities as few as one.

“The addition of Screaming Circuits extends our commitment to providing engineers access to a full range of design solutions from the best suppliers in the industry,” said David Shen, Group Senior Vice President and Global Head of EDE and Technical Marketing of Premier Farnell, parent company of Newark/element14. “We are pleased to add direct access to instant quotes for these PCB assembly services to the Knode on element14 to augment designers’ choices for doing on-line research and sourcing of best-in-class design solutions.”

Duane Benson

Sardines Seven Miles High

Being in the electronics industry means working on cool projects with cool people, but it also means other things. Like plane travel. I love flying. Not necessarily in an airplane though. I mean, I do prefer to be in an airplane when I'm flying. I'm more likely to have a subsequent flight if I first actually fly in an airplane rather than not in one. It's just these "big" commercial airplanes that we get stuffed into these days. Most of the complaints I read about relative to commercial flying have to do with the TSA or being stuck on a runway for six hours with overflowing toilets, but I haven't had those issues.

In point of fact, I don't think I've run into a TSA person that hasn't been polite. Especially in Portland. Still, even if they're nice people, I really don't like the idea of a choice between being nuked or groped. For the record, I chose to be nuked when I had to make the choice. I'm sure the government sanctioned groper wouldn't like it any more than I would, so I did us both a favor and stepped into the radiation chamber. I don't feel any worse for the rays. Maybe they were nice rays.

So, I don't have any complaints about the TSA. The crowds sometimes get me down, but all things considered, they aren't all that bad. What does get me is the straight jackets that they call seats these days. I'm in a motel in Milwaukee right now. I'll be heading home tomorrow. First in a mosquito plane to Chicago and then, probably, a 737 to Portland. I like the 737 in concept. It's a good plane. I just like being able to breath a little. It's natural to not have any room in the micro plane that I'll take to Chicago. It's not much bigger than my truck and will have twenty people crammed in it. You expect to be folded like a pretzel and spam crammed into one of those.

But a 737 is a big airplane. I can stand up in it and I'm not short. It's not like a little micro car. It's like my pick up truck (just not like it with 20 people in it). In the olden days, I preferred window seats for the view. Then I went for the isle seats for easier access in and out. Never the middle seat. Now, though, they keep taking leg room out so I'm not so sure. The seats get smaller every time I get on a plane.

If I take the window, I'm stuck for the duration of the flight with my knees just about in my face. Leg room in the isle seat is narrower so when I put my laptop bag down there I can't even wedge my feet under it to steel an extra few inches. Now that they charge for checked baggage, everyone brings their luggage as carry on and there isn't room to put both my suitcase and my laptop up in the overheads. I think they have the sky marshals throw you out the back window if you try to put both of your carry on's up top.

And so it goes. I'm just going to take whatever random seat I get and hope for the best. And I'll feel like a king if they grant me the supreme luxury of an entire 12 ounce can of warm soda pop.

Duane Benson
Curse you Red Baron!