PCB Exposure Test Strip

Making the PCB is not difficult using the photoetch process. I found an excellent set of instructions HERE on the web. All the necessary supplies can be purchased from Circuit Specialistsof Mesa, AZ. I used positive image photosensitized boards. These are boards that lose copper where light strikes them. The advantage of these boards is that the etching pattern is black lines rather that white spaces as with negative image boards. This makes circuit drawing much more conveninet. I used a CAD program to draw the boards and then printed the pattern on overhead transparency film.

The manufacturer suggests exposing the boards using a daylight type fluorescent bulb which they are only too happy to sell you. However you can use a strong incandescent bulb as well. The first step is to make a test strip to determine how much light exposure is required to get a clean etch. Too little light and no copper comes off the board, too much and the traces will be fuzzy. I simply made a test pattern and then exposed it to the light in increasing 5-minute intervals and then developed the board. As the picture shows, exposing from between 10 and 15 minutes at a distance of about six inches produced a good image.

Exposing the PCB

The next picture shows the exposure setup which is nothing more than a 120Watt reflector floodlamp spaced about 6 inches above the work surface. The PCB material and the etching pattern are held flat for exposure by a piece of plexiglass or glass. It is important to space the light source so that you get an even distribuiton across the surface of the board that you are exposing.
Once exposed, the board is then placed in a "developer" for about 3 minutes which removes the parts of the resist that was exposed to light. This leaves the resist on the traces behind.
The last step is to etch the board in standard ferric chloride solution to remove the unprotected copper between the traces. Here's what the boards looked like after etching. Another advantage of this process is that the photoresist is left behind on the traces where it protects the copper from oxidation. This eilminates the need to solder mask the boards to protect the copper.

Here are some finished PCB's for the CMOY amp and crossfeed adapter.