FabISP

The FabISP is an in-system programmer designed for production in a fab lab. This week, I used the Roland Modela MDX-20 to mill a printed circuit board for the FabISP. The mill uses a 1/64" diameter endmill to remove material from an FR1 (phenolic paper) printed circuit board. The remaining copper traces makeup the circuit. Then, a 1/32" diameter endmill cuts the outline of the board.

The next step was to solder the surface-mount components onto the board. A useful way to keep track of the miniscule components is to place them on a paper with a strip of double-sided sticky tape. Labels on the paper remind you what component you are working with.

Some mistakes I made:

1) I forgot to wash the PCB after milling the board. Certain types of flux, in adddition to finger oils, will corrode the materials on the PCB over time, so don't forget to clean your board.

2) I made the rookie mistake of removing the soldering iron too quickly from the board upon adding solder, preventing smooth flow onto the board and component. This resulted in clumpy-looking, weak solder joints as opposed to smoothly-curved, strong solder joints.

3) While zeroing the position of the mill, I bottomed out the height, meaning the endmill could not cut into the PCB because there was no more room left for the tool to move down. When you zero, make sure the machine still has room to be lowered. Then, adjust the endmill such that it touches the PCB.

Round 2

I am currently working on the FabISP key, which is a design created by Andy from a previous year.

Here was where I made the mistake of bottoming out the height of the mill. As a result, the traces did not cut deep enough, and I tried forcefully punching out the board, resulting in a jagged mess of a PCB.

However, I obtained something much cleaner after fixing the mistake.

The PCB design was altered slightly by Palash, in this year's class, and thus I used Andy's schematic to make sure the placement of the components was correct. Unfortunately, I have been unsuccessful so far in programming it.