Hey, everyone - I'm building a UV LED based light box for exposing Riston - type films, as one step in the production of PCBs. I started by choosing what I hoped would be the correct LED; 365 nM LEDs, each one rated at 3 watts. I wound up purchasing 20. I arranged them in 4 rows of 5, and came up with what I thought would be a cool idea: use a 200 X 300 mm PCB as the base and etch the circuit, polish the copper until it shone, and then tin plate it. The idea was that the PCB would serve as a reflective base, as well as being easy to solder.
I laid out the circuit board image using Microsoft Publisher (a desktop publishing program that has been largely abandoned by Microsoft). I started out by trying to transfer the image using toner transfer; that didn't work very well. I spent a lot of time trying to rescue the transferred image using felt tip markers, but ultimately gave up. Then i had a cool idea. I took some cheap self adhesive shelf liner I had laying around (they used to call this stuff mactac in my youth; vinyl with a pattern printed on one side, adhesive on the other, and a removable sheet to protect the adhesive) and I cut a 220mm X 320mm sheet of it. I then fed that through the laser printer, printing directly on the light colored vinyl sheet. Once printed, I removed the backing paper and stuck it to the PC board. Then I took a sharp knife, a ruler, and all my patience; and i carefully cut away all the vinyl sheeting where i wanted the copper to be etched. This worked out quite well; I etched the entire board, and got a great result. Once the etching was complete I washed and dried the board, stripped away the remaining vinyl... and polished the copper until it shone, using a metal polish called autosol metal polish. This stuff is magic; it will put a mirror finish on virtually any metal. Here's a manufacturer link:
http://www.autosol.com/product_p/1000.htm You can actually find this on Amazon, and I highly recommend this stuff. Best metal polish I've ever used.
Once i had it polished, I wanted to tin it. Tinning that huge board with a soldering gun would be a really slow show. There's some stuff called Liquid Tin from MG Chemicals (a proud Canadian company) which works well, but they want about $100 CAD for 16 fluid ounces of the stuff. So i did some digging, and i found a YouTube site called NurdRage where he comes up with chemical approaches to simulate existing products... and he had a formula for liquid tin! So I tried it, and it worked. Took me a few tries to get the plating effect I was looking for, and it still isn't gorgeous, but it is utilitarian. It will work. Here's a link to the YouTube video:
Then I spent some time soldering all the LEDs in place, checked my work, took a deep breath, hooked it up to my power supply and... success! Yea!
Here is the board after it was soldered, before i applied power:

And, here all those tiny UV LEDs are all powered up, and singing in unison:

...and the Murphys Law Gods have been testing my patience for the last hour, trying to get this post posted... so i think I will now retire, with as much grace and good will as I can muster. Enjoy, folks. I leave in peace. And pieces. >Charlie