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Step 8Mistakes
-Having the LEDs too close to the printed circuit board in the light box. The LEDs need to be sufficiently far enough for light to spread evenly throughout the circuit board. 10 inches away from the LEDs worked for us.
-Using textured transparency paper. The UV light did not pass through the transparency because of the texture. The solution is to use non-textured transparency paper. The photoresist will have little streaks of un-exposed UV. The MG Chemical brand transparencies worked well.
-Using sodium carbonate and sodium bicarbonate as a photoresist developer. Neither of these worked for us.
-Too much sodium hydroxide when used as a photoresist developer. All of the photoresist (including the non-exposed UV) was washed away in a few seconds. We suggest measuring the amount of sodium hydroxide and finding a mixture that works. If you don't want to spend the time doing that, use the MG Chemical photoresist developer.
-Adding sodium hydroxide while the PCB is already in the photoresist developer solution. This will instantly remove undesired parts of your photoresist. We suggest stirring the solution first, then dipping the PCB in the solution. If you need to add more sodium hydroxide, take the board out, add sodium hydroxide, stir the solution, then put the board in when the solution is mixed up well.
-Using "party" blacklights. We originally used three 4W party blacklights in an old scanner. The blacklights did work but not as well as the LEDs.
-Using a 500W halogen bulb. This bulb was too intense. It was difficult to find the correct exposure time.
-Using full size PCB's for testing. Don't waste your money using full size PCB's when testing, expecting the first board to work. Use a Dremel or paper cutter to cut a large PCB to save money.
-Using textured transparency paper. The UV light did not pass through the transparency because of the texture. The solution is to use non-textured transparency paper. The photoresist will have little streaks of un-exposed UV. The MG Chemical brand transparencies worked well.
-Using sodium carbonate and sodium bicarbonate as a photoresist developer. Neither of these worked for us.
-Too much sodium hydroxide when used as a photoresist developer. All of the photoresist (including the non-exposed UV) was washed away in a few seconds. We suggest measuring the amount of sodium hydroxide and finding a mixture that works. If you don't want to spend the time doing that, use the MG Chemical photoresist developer.
-Adding sodium hydroxide while the PCB is already in the photoresist developer solution. This will instantly remove undesired parts of your photoresist. We suggest stirring the solution first, then dipping the PCB in the solution. If you need to add more sodium hydroxide, take the board out, add sodium hydroxide, stir the solution, then put the board in when the solution is mixed up well.
-Using "party" blacklights. We originally used three 4W party blacklights in an old scanner. The blacklights did work but not as well as the LEDs.
-Using a 500W halogen bulb. This bulb was too intense. It was difficult to find the correct exposure time.
-Using full size PCB's for testing. Don't waste your money using full size PCB's when testing, expecting the first board to work. Use a Dremel or paper cutter to cut a large PCB to save money.
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