Sunday, September 26, 2010

Homemade Double-Sided Printed Circuit Boards

I decided to try my hand at double-sided printed circuit boards while I was working on my Surround-Sound Headphone (SSH) amplifier. Up to this point all of my PCBs have been single-sided, with wire connections on top to hop traces. Some of the big advantages of double-sided boards are higher board density, fewer wire jumpers, and the ability to easily put surface-mount components on either side of the board.

I use the free program ExpressPCB to generate my printed circuit boards. I do not use the mail order PCB service. The program allows printing of the top and bottom traces, but the top traces will not be mirrored properly to iron on. So I used a program called CutePDF which creates a virtual printer that you can create PDFs of the printed images with. Then you simply open the top layer in Adobe Reader and print it mirrored.

This is a thin (.030") double-sided board I purchased that can be cut with heavy-duty scissor/shears. The method to get them two sides aligned was putting both sheets of photo paper together, taping the edges, and sliding the board in between. Then I iron on both sides for about 5 minutes. Then I toss the whole shebang into hot soapy water for 10 minutes, and remove the sheets gently. The results:

After etching in ferric chloride, and removing the toner with steel wool, I took a look at the board in front of a bright light source. The traces on both sides line up perfectly! It worked!

I went ahead and drilled the board by hand with my dremel and a carbide drill bit. I have several bits for various holes sizes on the board. Then I populated the board with components, and tested the circuit. I usually start by first populated the power-supply section to make sure that's working, and then move onto the rest of the circuit.

I added a chunk of aluminum as a heat sink for the voltage regulator. It was getting warm during testing. Those wire links are actually supposed to be output resistors, but they ended up not being needed for that section of the amp. The amps with resistors are for load-sharing the current between both sides of the dual op-amps, allowing them to drive lower impedance (16 Ohms, etc).

Only a few top traces were actually needed on this board, so it probably would not have been worth it if I wasn't trying to verify my process. This was a great success, though. Amplifier board for the SSH amplifier complete!

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