For the White Star Balloon project, one immediate need was for an extensible Main Flight Computer platform. In order to facilitate development, a completely modular design was needed.
In brief, this board uses the I2C bus to communicate with multiple slave modules and sensors in order to accomplish the task of managing our balloon’s flight. More information can be found at our wiki.
To fabricate these PCBs, we chose Gold Phoenix, located in Hubei, China. They offer some really incredible deals on PCB manufacturing, including $100 for a 2-layer board, 155 Square Inches, 5 day turnaround + 3 days shipping. We chose this fabrication house since Sparkfun uses them for their own products, as well as BatchPCB services.
Much more below the break.
Knowing the Design Limits of the board house, the board was designed with a margin above this. The $100 service gives you up to 8 mil trace width and spacing. For this board, most traces are 12 mils, while the remainder are 10 mils. Most traces have a separation of at least 15 mils, while some are as close as 10 mils. The ground planes on either side of the board have a 12 mil isolation from surrounding components and traces. The text is primarily 66 mils in height, at an 8% aspect ratio, while some pinout text is only 32 mils in height. If this doesn’t mean anything to you, no worries!
In order to place an order with Gold Phoenix, you simply zip your Gerber files and send an email describing what you need to a sales representative in Canada. It’s a little odd sending stuff like this to an arbitrary yahoo.ca email address, but it works out. A human will be looking at your files every step of the way, so some extra description about how the Gerbers fit together definitely won’t hurt.
When they calculate the number of boards they receive, they divide your project’s size by the board size, in our case, 155 / 6.15. This yields 25 boards, even though there would be no way to fit 25 of these PCBs on the max panel size of 14.5″x10″.
When I got the boards back from the fab house, they looked like this:
I could not be happier at how these turned out. I was quoted for 25 boards, and received 27. Even the portions of the board which came really close to the fab house’s design limits turned out great! I can’t spot a single electrical error on any of these boards. The Silkscreen registration is a little off on a few boards, although there’s only one PCB for which this may become a problem.
Of course, the first thing I did was solder it together.
Unfortunately, I can’t say the same about quite a few other properties of this board. My Cad files had a few errors on them which weren’t caught before the board was sent for fabrication. Gold Phoenix faithfully reproduced these errors, and a few components won’t work properly. The pinout for the temperature sensor was mirrored horizontally and vertically, and the landing pattern for the Real Time Clock on the reverse of the board used an SO16 pattern instead of an SO16 Wide pattern.
Fortunately, this design’s modularity means that neither of these errors are fatal. The barometer includes a temperature sensor, and timing data can be received from a GPS unit.
In the mean time, the project keeps hammering forward.