UV LED PCB Exposure Box
During the process of manufacuring of homebrew PCBs you need to expose the photosensitive film with ultraviolet light. A cheap and low power solution can be found in UV led strips.
They can be found for around 3 euros per meter on Chinese retailer websites. In my case I bought 2 meters of SMD5050 LED strip. They contain 60 LEDs per meter and the strip has current limiting resitors in place, so you only need to supply 12V with enough amperage to light them up. The resistor is 240 Ohm, so 12V will limit the current to 50mA per LED. Take into account that 120 LEDs will require 6 ampere of current.
Next you will need some kind of container to house the LEDs. I had an old scanner, which I dissasembled and described it in my previous blog post. It was a perfect fit to place the UV LED strips.
You will also need a light diffuser. I had an old broken LED TV panel, and salvaged a sheet from inside. There are multiple layers present, but I only took one of them. It is also possible to use parchment paper for that purpose.
Cut the strips into the size you want. In my case it was 25 cm. (15 LEDs per strip). Actually I wanted them longer, so it would cover the whole area of the scanner, but was limited by my supply. I also reasoned that I will be probably not making PCBs that are larger than 25 cm in length.
Now solder the stips together with wire just like this.
It's time to test the LEDs. Luckily they all light up. I have used a 12V 1.5A power supply. It does not provide full power to the LEDs, but I think it's bright enough.
Now let's attach them inside the scanner casing. They are provided with self adhesive tape.
I also soldered a DC power supply jack socket,
and attached it with with hot glue to the casing. It will not win any beauty contest prices, but it's firm in place. I also coverd the hole on the back (that was used to connect the parallel ports) with a metal PCI slot cover.
Tested it again and it still worked. Well, actually the first time I hot glued it, it didn't... So I had to remove everthing and re-check my soldering.
I have cleaned the glass from fingerprints and taped the diffusion layer on the bottom of the glass with scotch tape.
The glass could be slid in place and the side stips placed on top of the glass.
With the lid placed it is finished.
I am also planning to install a display with a timing circuit. But this is material for another project.