Keyword: pcb board, PCB
Build your UV LED light box. Elevated transparent plastic/glass is used to hold the transparency paper and presensitized copper clad about 10 inches above the LED. pcb board The transparent plastic was taken off a picture frame purchased at Goodwill. Keep in mind that some plastics/glass pcb board do not allow UV light to pass. Some experimenting is needed to find one that works well. The picture below shows how Monnie arranged the LED on the breadboards purchased at RadioShack. We spaced the LED out by 6 holes from all sides. Banana jacks were inserted in the backside of our box to be powered by a benchtop power supply pcb board.
Draw your circuit schematic pcb board. Once the schematic and layout are drawn, it is time to print the layout onto a transparency. To print only the desired circuit, turn on only the Top Layer, Pads, Vias, and Dimension. This is done by selecting View -> pcb board Display/Hide Layers in the Layout editor and selecting the correct settings. The Layout is now ready to be printed, make sure that the image is mirrored so that text shows up correctly after being transferred onto the PCB. We printed the circuit with our Brother HL-2070N (on highest quality) laser printer and MG Chemicals transparencies pcb board.
Expose the presensitized circuit board to UV light. Place the printed transparency on the elevated plastic about 10 inches above the LED. The ink should be facing up towards the sky. While the room is somewhat dark, peel the white film off the presensitized circuit board to expose the photoresist. Place the PCB on top of the transparency, photoresist facing pcb board down towards the LED. Stack about 8-10 textbooks on top of the PCB to make sure the photoresist is tightly pressed against the ink of the transparency. No scotch tape is necessary to hold the PCB down to the transparency. Turn the UV light box on. Exactly 1 minute exposure time worked well. You may have to experiment with different times depending on the height above the LED. Turn off after 1 minute. The photoresist pcb board will look exactly the same after it has been exposed to UV light. We could not tell the difference between an exposed board and a non-exposed board.
Prepare the developer solution. Prepare the MG Chemical developer solution with 1 part developer, 10 parts tap water. I used 1/4 cup developer, pcb board 2 1/2 cups of tap water. Be sure to mix the solution with tap water thoroughly before placing the PCB in the solution, otherwise the photoresist will be eaten away in undesired spots. Place the PCB in the mixed solution and shake it around face up pcb board. The parts where the photoresist was exposed to UV light will be washed away in about 5-10 seconds. Do not leave the board in the developer solution for too long, otherwise all the photoresist will be washed away. Place the PCB in cold water immediately to stop the reaction once the board is finished. The developer solution can be re-used for multiple PCB. You could try using Sodium Hydroxide (Lye from Ace Hardware) but you will have to experiment with what % to put in tap water. pcb board The percentage of Sodium Hydroxide to tap water is important because too strong of a solution will wash away your non-exposed UV photoresist pcb board.
Etch the copper away.pcb board Prepare a solution of 1 part Muriatic Acid circuit board, 2 parts hydrogen peroxide. I used 8 oz. Muriatic acid, 16 oz. hydrogen peroxide. Be very careful with this acid, it's a lot stronger than the photoresist developer. I suggest using a fan over the bucket so you don't breathe in any of the fumes. Wear gloves and goggles pcb board. Add the PCB to the solution and shake the bucket carefully. The solution will start to turn green as the copper is being etched circuit board away. As soon as all the copper is etched away, remove it from the bucket. The copper will take about 2 minutes to be etched away completely pcb board. Wash the PCB off in a bucket or use a hose.
Remove the photoresist Remove the photoresist with Acetone and pcb board a Q-tip. The photoresist will come off very easily with a Q-tip dipped in Acetone. Keep using new Q-tips until the Q-tips pcb board are white after you have swabbed the board.
Populate your PCB with parts At this point, you have a PCB to populate with integrated circuits and parts. Enjoy your PCB and let me know if you have any questions.
Mistakes -Having the LED too close to the printed circuit board in the light box. The LED need to be sufficiently pcb board far enough for light to spread evenly throughout the circuit board. 10 inches away from the LED 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 pcb board. -Too much sodium pcb board 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. -Using a 500W halogen bulb. pcb board 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 circuit board, expecting the first board to work. Use a Dremel or paper cutter to cut a large PCB to save money.
