Screaming Circuits: August 2009

Open Source Hardware

The open source movement has been a pretty big factor in the software world for many, many years but it just now seems to be rearing it's head (why do we say "rearing it's head". Shouldn't we say "fronting it's head"? Maybe "rearing it's behind"???) in the hardware world. Yes, it has been around with HW, but more silently in the shadows then as an actual productive movement.

We built some Beagleboards with the open source design materials. The Arduino has become quite popular over the last year as an open source platform and we've build some Arduino derivatives. I'm sure there are other open source HW projects out and about as well. Those two just seem to be the most visible at this point.

180px-Arduino_DiecimilaSo, the big question is: "Is open source hardware ready for commercial applications?". You could argue day and night (and people do) as to whether open source Linux is ready for the home computer, but there is no dispute that open source software is ready for commercial use. A good portion of the Internet runs on open source servers. No question about it.

The Arduino was originally designed as an educational product and is quite well suited for that. It's also a great hobby platform, using a simple 8-bit AVR processor and a C++ish programming language. As such, it works pretty well in the hobby world but also has plenty of commercial application potential.

The Beagleboard uses a new Texas Instruments processor that has enough power to render full-motion video. If a little 8-bit jobbie can have commercial applications, the Beagleboard most certainly can too. Further, the Beagleboard design came out of Texas Instruments. They set up the group that put it all together and the result it's a world-class design implementation. Software only folks can buy a pre-built Beagleboard from Digi-key or Special Computing and hardware folks can use the design as an inspiration, use chunks of the design, just produce a board from the exact files (as we did) or any combination thereof.

Personally, I think it's a brilliant move on Ti's part to do this. Mechanically, the part, a .4mm pitch BGA with a .5mm pitch BGA memory chip on top of it in a package-on-package form factor, is very difficult to use. The escape routing alone is a good challenge at that ball pitch. As it is, the open source design files are a great head start for anyone that wants to use the processor. It'll get commercial customers buying the processor a lot sooner then if everyone had to start from scratch. And with the fully-built board also being sold for $150.00, a whole lotta software people can poke around with it and make everyone's job easier.

Duane Benson
Arduino was named after a tavern. What was Beagleboard named after?

Note that "Arduino" is a tradmark of the Arduino team and "Beagleboard" is a trademark of The Arduino picture used came from Wikipedia and was uploaded by someone identifed only as "Randomskk".

Vias under Power Transistors

Normally, a power component like this would have a big pad and some heat dissipation space under the heat slug. It might even have thermal vias going to another heat pad on the back side of the board. If it's being run at anything close to it's full current capability, that would be a requirement. This one is probablyVias under thermal pad a bit underutilized though, rendering the big pad un necessary. It's still a good idea for mechanical strength, but in the prototype world, we don't always follow the rules.

The problem here though, is that the open vias under the part can short to the thermal pad. That's bad mojo. Some board fab houses can put a solid coat of mask over the vias and they'll be okay. Not all board houses will do that though, and if the board has a silver finish (this one is HASL), you wouldn't want the vias sealed because silver vias can outgas and corrode if completely sealed.

We just put something non-conductive between the part and the board and it's all fine, but as I've said so many times before, that's not best-practice, even for a proto, and it's doubly not good in a production environment.

Duane Benson
Connect the 16 via dots and what do you get?

OMAP3530 Package on Package Layout

If you've read my prior post, you know that we've built up some package on package (POP) boards. We built up some test boards with dummy components and some working Beagleboards. For the Beagles, we didn't do any of the design or layout work here. We just used the open source Gerbers and BOM files provided at

BB pop cut out populated I've been reading through the message board and pondering the issues related to such a design. At first thought, it seems that placing the part in the layout program shouldn't be too much of a problem. I think most CAD software will just let you set one part on top of another. You may have to ignore the DRC checks for that part, but other then that, it shouldn't be a problem. The Centroid (X,Y,theta) file shouldn't be a problem either. The two reference designators will just have the same XYt value.

What I'm really wondering about though is the library component - the footprint. How do you make a component with pads on the top, in addition to pads on the bottom? What copper layer would you put the top pads on? You'd need to put the pads for the top POP part on that missing copper layer too. Will CAD packages let you create extra copper layers with a Z-offset? Layers that float in the air? Weird.

I don't have much experience with big-system CAD packages so I don't have the answer to these questions, but I expect it's probably not to difficult. Here's my first guess: just make an extra layer and call it pop layer. In the library tool, put the top pads of the OMAP chip in that layer and the regular pads of the POP memory chip also in that layer. Then when you export the Gerbers for board fab, don't include that the pop layer or at least make sure the fab house knows that it isn't a copper layer (or any other layer to go on the board).

On the other hand, I guess maybe you could just not worry about it and in the schematic and layout, simply treat the POP set as one chip. Just make sure that the assembly files (Centriod, BOM and any build instructions) tell the assembly house where to place the POP part. Hmmm. I don't know what would be best.

Has anyone reading this made a POP layout? What did you do?

Duane Benson
Goober snorts

Beagleboard and Package on Package Assembly

So, what's the big deal about the Beagleboard and us building it? If you aren't familiar with it, check out for all the details.

In short, it's an open source hardware design development board / embedded system utilizing the Ti OMAP processor and a Micron memory chip in a POP (package on package) form factor. The POP is the significant point here. Well, that plus some 0.4mm pitch BGAs.

Beagleboard we built cropped  
We assembled this one. The image below left is AbiWord running on the board pictured here.

The Ti processor is a 0.4mm pitch BGA and the Micron chip that goes on top of it is a 0.5mm pitch BGA. The power management / audio chip on the Beagleboard is also a 0.4mm pitch BGA. That's some pretty tough stuff and not a lot of folks can build it. Not only can we build it, but we can build it in small prototype quantities - as few as one at a time. We're proud of our capabilities and dedication to both quality and on-time delivery. (So, yes, there is a bit of self-horn blowing here.)

BB we built screen shot sm If you're primarily a software person and just want a working beagleboard, the least expensive route is to go to Digi-Key or Special Computing and buy one preassembled. But, if you want a derivative design, or just any old design using a POP part, you'll need someone that can build it properly. We've been assembling small volume prototypes of difficultAmkor POP sm designs for over six years now and we love doing the tough stuff. From 0201 passives, flex boards, rigid-flex and now POP. We also do easy stuff.

The beauty of the open source design is that Ti, through the Beagleboard organization, has made the Gerber files, the schematics and the CAD files available open source. That can give you a significant head-start in getting your custom design up and running. And, then, once you're done and need someone to put all of those parts on the boards and chips, connect up with us. We can assemble it for you. This is considered a special process, so you'll need to get confirmation from us on what turn-times we can support for your specific board before placing the order.

Duane Benson
Quaffing root beer with Bill Mauldin

Gold Fever

We call it Gold Fever. It's when you've got a hankerin to have a nice flat surface to put that BGA on and the lust for that precious metallic surface turns into an obsession. It's all you can think of. You forsake your family, your job and even your level 68 Night Elf druid for but a glimpse of that resident of period 6, group 11. Ahhh, yes (or Auuu, yes), the all desired number 79...

Gold fever Okay, maybe we don't call it "gold fever", but it certainly can cause you a fever in your time line and budget if your gold board comes back with spots like this one did. In addition to the obvious four spots with visibly degraded Au layer, this whole set of PCBs probably has black-pad written all over it. If you have other boards that came from the same batch as one like this, you should give them a very close examination. At least make sure you've got a good healer class in your guild.

In case you haven't been caught by the scourge of black pad, just know that the Argent Dawn can't help you here. Black pad is caused (and I'm generalizing, not going into exact technical details) when there's a little contamination in the nickle layer of an ENIG (Electroless Nickle Immersion Gold) pcb during fab.

When the component is then soldered on, the solder mixes with the gold but not the underlying nickel layer and the part can later pop off or at least not conduct your signals or complete your quests. It's most commonly associated with BGAs, but can occur with other types of components too.

Duane Benson
It's safe back here in Goldshire, but all I can find is copper.

Wide Load - Skinny Room

Here's another example of parts that looked like they would fit based on the outline in the CAD program. Cut tabs angle 2 Parts don't fit angle 2 The silk screen outline printed on the board showed a cozy fit, but a fit none the less. However, in the real world, the connectors have those tabs sticking out each side and they wouldn't fit that close side by side. The solution was pretty simple, but as the broken record says, you wouldn't want to do this in a production environment. We can just figure out how to make a lot of stuff work for your protos, but this board will have to have some layout changes before going in to production.

This reminds me a lot of those little garages found in "starter homes" these days. Yes, the architects and builders can say that the house comes with a full-size garage. They just don't tell you that it's only full-size in the sense that it could fit a full-size Yugo or MG Midget in it, and then only if you don't put so much as a broom in the place for storage. Or more so, it's like the "bigger" starter homes with two car garages. Just make sure to remove your side-view mirrors as we did with these parts here because there isn't room for both cars with anything sticking out the sides. And your cars need to be hatch backs so you can actually get out of the car.

Duane Benson
Clip, clip. Snip snip, Oh what a fine fit it is.

Oopsie in the Center Pad

Darn. This PCB don't look so good. Quick - name two things wrong with it...

Center pad oops 1 

If you guessed that the solder mask is inverted and the vias are open, then you were right. Sorry. No points will be given for this exercise. It's just something that happens now and then and a good reason to double check those Gerbers before you send them out to fab.

So, what happened to this poor pcb? Did it get shipped off to the great recycling heap in the sky? Well, not this time. If it were a production build, it would have been chased out of here faster than a speeding Smart Car. But, as it was, this was a proto build and we got creative.

Center pad oops 2 

A little careful scraping with with a sharp object and viola. We don't recommend this as a solution and we won't guarantee that it will work, but sometimes it will do in a proto world, as it did in this case.

Duane Benson
Scrape goes the weasel

Upcoming Maintenance = New Goodness!

On Tuesday 8/18 starting @ 3pm Pacific Daylight Savings Time, our site will be offline for a bit as we make a few upgrades.

We expect to have everything back up and running by 5pm PDT or sooner. We apologize for the inconvenience!

If you have questions or need to place an order while we are away, please don't hesitate to call 1-866-784-5887 or email us:

What "new goodness" are we adding?

Just you wait and see... I wouldn't want to spoil the surprise!

Matt Mirande (new-ish guy)
What can't you build with a hammer?

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