PCB Board Development

Step One: Developing the Photo Tool

The first step is to develop the photo tool. To do this we print out the copper layer on normal printer paper with ink that's thick enough for light not to go through. Just as photographer develops a picture in a dark room, we will be developing the photo tool in this room. Using a sheet of film (similar to what cameras use), we place it over the print out. Using UV light, we produce the image by having the light emit through the paper and onto the sheet. Once this process is done, we quickly grab the film and place it into one of three liquids, the developer. The chemical darkens all areas where the UV light manages to go through. The next is water, which stops the process of the developer. At this point we check to see if the film is under or over developed. If it's under developed, the film goes through developer again. If it's over developed, then the film is ruined and the process is repeated. Otherwise, if it's perfect then we place it into the last chemical which finalizes image such that the image remains permanent. We now have a finished photo tool. When looking at the tool you will see that all the copper traces are clear and all remaining areas are black. This technique is an out-dated approach to producing the photo tool. In a professional setting, a print out isn't used to make the photo tool.

1. Expose file to UV light through printer paper.

2. Process film in chemicals.

3. Photo Tool Done!

Step Two: Transfering Design to Board

Now we can transfer the design to the board. For this part, we once again have to be in a dark room. At this point we take a board containing copper on a side and heat it in an IR oven. Once heated, we then place it in a machine that laminates it with a photo resistant material. When exposed to UV light the photo resistant material hardens. To get the pattern onto the copper layered board, we place photo tool between the UV light source and the board. Only the areas where the traces are located is the photo resistant material hardened. The next step is to place the board into a machine that spays chemicals onto the board. In this step the areas where the photo resistant material is still soft gets dissolved. With the unwanted areas exposed we then take it to another machine that will dissolve the copper in the exposed areas in the same manner as the other machine. At this point the board starts to look like a circuit board. Now we need to dissolve the remaining photo resistant material. To expose the remaining copper, we dip the board into hydrochloric acid to dissolve the hardened photo resistant material.

1. Heat copper board with IR oven.

2. Laminate board with photo-resistant material.

4. Expose traces with chemicals.

• Chemically etch photo-resistant material
• Chemically etch copper layer
• Rub off remaining photo resistant material with hydrochloric acid

5. Cut out individual boards and go to the next step.

Step Three: Drilling Holes in Board

The final step is to drill the holes in the board. This is where producing an NC drill file from the PCB editor comes in hand. At this point you load the file into an automated drilling machine which drills holes in their correct location. Depending on whether or not the machine can handle multiple hole sizes, you may need to use a drill press to widen some holes. At this point, all that's left is assembling the board. If this were done professionally, a silk screen would be applied labeling all the components.

Automated drilling machine. A floppy disc with the NC drill file would be loaded into the coputer and the machine would drill the holes after calibration. This particular one can only do one particular drill size.

This drill press is used to widen holes or manually drill holes into the board.

Notice how the professionally-made board is a lot cleaner than the rough board.