The basic concept of the UV etching method in creating a printed circuit board is to use ultraviolet light to soften and eliminate a substrate and use the retained substrate to shield the copper board from an acid bath.
In creating a two-layer copper circuit board, you need the following materials: copper (coated with positive UV resist substrate), Sodium Hydroxide (NaOH) to dissolve the substrate coating, UV lamp, UV translucent plastic to weight down the PC during exposure, transparency sheets, and a small drill bit (.031).
In designing the printed circuit board, it is crucial to take note that vias is quite difficult to deal with, so it will be to your advantage if you try to minimize the use of it to your layout. Once you are done with the layout, you need to set up the PCB software so that it will only print the things you want in the copper board.
In preparing your board, you need to mark the parts where you will be cutting using a pair of calipers that are quite handy in etching precision marks in the protective sheet. Then, you need to cut the printed circuit board to its appropriate size. You can use tin-snips but a dremel tool will work fine.
It is crucial to mirror the top layer because you need the actual PCB to be as close as the diagram as possible. The diagram should be clear when showing which side goes towards the printed circuit board because it will have a matte finish.
Many technicians are a bit scared of creating 2-layer printed circuit boards because these are quite difficult to line up the two layers. However, this is not actually that hard particularly if the board is small. All you need to do is to use a drill press to align the reference holes. Remember that the farther they are apart from each other, the easier it is to avoid misalignments in the rotation.
The next phase is regarded as a time-consuming step. First, you need to be extra careful in removing the protective sheet of one side of the board. It is recommended to do this at night or at least in a room because sunlight is a good source of UV light, and it can result to undesirable effects.
Then, align the artwork sheet with the circuit board and use a scotch tape to secure it. Place it under a transparent sheet and under a UV light for at least 15 minutes. If you wait a bit less, there will surely be substrate on the board. If you wait a bit more, you might end up washing off all the substrate during the acid bath.
Developing the printed circuit board is regarded as the coolest part of the whole process. You need to prepare a solution first to develop the PCB. You can use a clog remover mixed with water. However, there is always the possibility of overdoing it using a developer concentration. You can have the developer wash away all the etch-resistant substrate because of high concentration. Hence, be always sure to take note of the concentration that you are using so you can make the necessary adjustments.
Wear a pair of rubber gloves and immerse the circuit board in the developer and rub it with a foam sponge. Be very careful in this process because some clog remover solutions can melt away certain types of foams. Meanwhile, be sure to follow the etching process, which may take at least three to five hours.
After etching the circuit board, the next thing to do is to drill all the holes. As mentioned above, it is best to use a 0.31” drill bit alongside a tabletop drill press. This part is quite easy as the small copper vias can guide your drill into the holes.