So, last year I spent close to 100 hours laying out my smallest circuit board, even to this date. The only problem is that I couldn't get it to work. I think I figured it out. I made the mistake of designing the board around a quad flat no-leads, or QFN, Propeller Chip microcontroller. In hindsight, I should have used a quad flat package, or QFP. QFN's are notoriously difficult to solder, and still often develope solder bridges. A solder bridge is a when two or more adjacent pins develop a 'slick' of solder that bridges the pins, making them electrically connected.
Cut to a few days ago. I got 4 boards in the mail from Advanced Circuits. A couple weeks before that I put in a new order for my matrix boards, with a few minor tweeks to the original design. This time I elongated the pads for the QFN prop chip. Hopefully this will wick the extra solder away from the Prop's pads and help prevent bridges. We'll see.
I realized I have explained what the boards do; here's a summary:
- Parallax Propeller chip
- 64 0603 surface mount LED's arranged in an 8x8 row/column matrix
- Two choices of lithium polomer battery
- On-board battery charging when plugged into USB, via MAX1555 chip
- USB programming via FTDI FT232RL chip
The point of the board is to allow the user to program it to display messages on the 64 LED's. Another possibility reccomended to me on the Propeller forum is to Program it to play Conway's Game of Life.
I've been extra busy in school these days, so I'm not sure when I'll get a change to solder up one of the new boards. But I'll be sure to post my results here. For now, I'll leave you with a photo of the tightest (in both senses) board I've designed.