This week we worked on making in-cuircuit programmers. This included milling circuit boards, soldering elements onto the board and programming the board.
Milling the Board
We milled our boards on a Rolland milling machine. The machine cuts shallow paths out of the copper boards to create circuit paths.
We used a pre-designed template for the boards which we downloaded from the fab website and sent to the machine to direct its milling path. We used a 1/64" bit for the milling.
The next step after milling was to make a cutout of the board the cutout ws made with a 1/32" bit. To secure the board on the machine for milling and for the cutout, we used double-sided tape. It was important to lay the tape evenly on the underside of the board to and prevent overlapping. The scale of our milling is 1/64 of an inch, which is not too different an order or magnitude from the thickness of the tape.
We then soldered the circuit elements onto the board, including resisters, diodes, jumpers etc. as per the design of the board.
Soldering is a little intimidating when you start, but I quickly learned that melted solder will not flow all over the board even if you accidentally melt too much. It has a high surface tension and tends to stay by itself in small balls. It also likes copper and heat and tends to remain on the copper elements of the board, as well as any hot elements. It will quickly solidify when heat is removed, making it a lot easier to keep it where you want it to be. I also found the flax and copper braid helpful in clearing up messes.
We set the soldering iron to a temperature of 700F. This is a little high, because solder will melt at a temperature as low as 400-500F, but I found that a higher temperature helped me work easier and faster with the solder.
I started with the smaller components: the resistors and diodes and finished with bigger ones which tend to get in the way.
We programmed the board with a program from the Fab Labs. After programming we removed the zero ohm resistor jumpers.