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PCB UV exposure box

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AdeV:
Some time ago, I started to make a UV box to expose PCB photoresist (and possibly other UV-curing applications, e.g. diazo process screen printing, of PCBs and/or front panels, and the like).

Un-seen by the camera, I soldered dozens of UV LEDs I got cheep from fleaBay onto a couple of Eurocard sized strip-boards, spending many happy :scratch: hours getting the damn things the right way around, in the right holes, and all connected up...

Later, I spend many hours designing and breadboarding a supremely over-complicated timer control unit, complete with rotary encoder for programming, and individual control of the top and/or bottom light panels. Then everything went into hiding for a few months while the office was plastered/painted, until a Round Tuit got unearthed the other day...

So, finally, a couple of reasonably productive days in the office resulted in a pile of precision-ish parts (see exhibit 1):

* A piece of glass sized to exactly somewhere around 110x160mm
* Aforementioned circuit board covered in UV LEDs
* four aluminium sides, the two long sides with grooves cut 0.8mm down x 2mm wide x 2mm deep (for the glass) and a bit lower x 1mm deep for the light board
These were then carefully-ish assembled, and after much fettling, more or less went together as expected per photos 2 & 3.

Finally, the assembled box was popped into the case I prepared for it much much earlier (by stripping most of the foam padding out - mistake!), lashed up to the breadboard circuit, and tested. Works well! See photo 4.

Now I just need to remember to bring my special PCB tracing paper down to the workshop tomorrow and I'll have a crack at actually developing a PCB!

So... things I have learned so far:

* Never, ever, try to work with glass! What an evil material! Copper rod is a joy by comparison... Note the cracks in the glass (getting bigger all the time), some acrylic has been ordered to replace it.
* My milling machine has a problem with its brake. Currently, it'll only work with the centre bearing cap removed  :scratch: Another fixer-upper project in the offing.
* Did I mention not working with glass?
* Wickes cheapo tile cutter is actually reasonable on glass, but it's definitely best not to work with it. The glass OR the tile cutter.
* Always always always use the proper tapping head on the mill when power tapping. Don't ask me why (see photo 3...).

awemawson:
Beware that acrylic sheet is available in UV transmitting and UV blocking versions as I understand it.

(mine uses glass sheet and UV fluorescent tubes)

tom osselton:
I have a carbon arc platemaker that was used for printing would that work for that blue resist paper?

AdeV:
Hi Tom,

Interesting device... it'd probably do the job, I expect the exposure time would be only a few seconds!

Aaanyway, PCB experimentation time was limited to this afternoon, as the water supply was frozen down here this morning. Once the pipes had thawed & no bursts were apparent, it was time to crack on. See attached photo...

#1: Clearly badly over-exposed (that was 4m 30s). Tracks are missing and the big pad has a bit missing too.
#2: 2nd attempt, this time with 2m 30s. Better, but I'm still losing tracks in places.
#3: Aaah, now we see what's going on. This one is under-exposed... except where the tops of the LEDs are.
#4: Another attempt, I've lifted the board up on a temporary structure (and managed to finish breaking the glass  :palm:) This one is nearly usable, except for the side tracks are still virtually gone.
#5: Last go tonight on a little offcut I had left over. Much better - somewhat shorter exposure time (2m 30s again). A smidgeon of resist has resisted dissolving, so I may need to go to 2m 45s or even 3m to get the final effect. Ignore the slightly blurry looking tracks on the RHS, the board was slightly curled up due to the way I cut it, and I didn't dare weigh it down properly.

On the bright side, my home-made Sodium Meta-silicate (aka water-glass) developer worked just fine, if a tad slowly. For hobby stuff, I think slow is probably better than fast, though. Next job, once I've re-made the box & put an acrylic top on it (hopefully all arriving in the next couple of days), is to mix up some Cupric Chloride acid to etch the copper  :thumbup:

seadog:
..."mix up some Cupric Chloride acid to etch the copper"

Don't you mean ferric chloride?

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