Thursday, June 26, 2014

More Homemade PCBs

Fail! Fail! Fail!
After numerous failures I think I may have a board I can use.I thought I had made good enough notes when I made the LEDTester board a while back, but???

This time I am trying to make the Sparkfun's Serial Enabled LCD Kit. They have posted the eagle files so I can change them if necessary. I didn't notice the trace width until after the first PCB failure.

The target, used w/o permission from Sparkfun.

I am using the presensitized positive photo resist boards with inkjet on transparencies for artwork still. And exposing in the direct sunshine which is just fine here near the equator. Kinda limits me to daytime PCB work though.

A weeks worth of failure from right to left. The left may be good.

The one on the right looked good, but I had forgotten what they looked like when finished etching. I took it out too soon and cleaned the resist off. The traces were too thin and were being eaten away anyway. After a lot of googling, I found how to increase the trace width, fix the errors this caused and get ready to try again.

The second board from right I noticed wasn't exposed enough, so I trird to re-expose it and develop it some more. Bad idea! I also got it out of the etch too quick. For each of these I had printed black grayscale from the default colors of eagle. this did not turn out to be opaque enough in the UV range to work but I blamed it on the other steps.

The second board from the left also failed. I printed it as color photo on photo paper. I also found a reference to a script(drill-aid.ulp) to run in eagle that makes all the holes smaller so it is easier to start the drill when hand drilling the holes for the parts. It draws a small circle with crosshatch in the middle of the hole to be drilled. Between it and the light color of the pads, when I printed the transparency, the pads pretty much disappeared. I etched it anyway to see for sure I could.

Top and bottom artwork taped like a hinge with tiny registration marks.

So the right answer seems to be, check the boxes for black and solid in the eagle print dialog, print photo color to photo paper even though it is a transparency. Then expose to sun 2 minutes per side covering the back side. Develop about 3 minutes in warm (not too hot, board 2) caustic soda until the extra resist washes off. Then etch in warm muriatic/peroxide till you see the board. You can take it out, rinse and check along the way.

Another view of the art and the board.
It looks better in person, I guess it is not very photogenic! HA.
Next to try to drill the holes by hand without destroying it.