Like many Arduino lovers, once I began creating larger projects I obviously did not want to keep them on a fragile breadboard. As many people do, I started to assemble my projects on cheap prototype boards. While these boards were fairly rugged, their layouts were confusing to say the least and were basically organized chaos! So I learned how to etch my own circuit boards. While there are several ways to go about making your own boards, with the two most popular being toner transfer method or the photo-resist method .. I chose to go with photo-resist using pre-sensitized boards. This involves designing your board in software such as Eagle CAD, printing your circuit out on transparency film with a laser printer, exposing and developing the board with a light source, and finally etching the board with ferric chloride solution. My very first board came out perfect to my surprise but it was pure luck. As I made more boards I quickly found out that I never achieved the same results twice. What I found out is that the exposure time and the distance between the board and the light source must be EXACT every time. I was over or under exposing my boards most of the time. I wanted to make my own fool-proof exposure box that #1 would expose each and every board in the exact same way with evenly-distributed light and #2 precisely time the exposure of every board down to the second. I also knew that using UV light would greatly reduce the required exposure time.
It was well worth the effort! I found that the perfect exposure time for any board was only 2 minutes – 15 seconds for a 4x3 PCB, which is generally the maximum size of nearly all of my projects. This exposure box is specifically made for 4x3 inch boards, but can be scaled up if your projects demand larger boards.
So in the end I simply print and cut out the 4x3 transparency film, lay the film glossy side down in the exposure window, peel and place my blank PCB into the window (which fits like a glove), enter my exposure time, press START and walk away!
And again keep in mind that I designed this box especially for 4 x 3 inch boards. You can easily scale the project up or down by simply adjusting the window size AND the number of UV LED's used. I would estimate 9 LED's for every square inch of copper.