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How do you do your PCBs?
PekkaNF:
One more distraction: How does the vacuum system works on two sided UV PCB exposure unit?
I only have used method were PCB is slipped in a artwork and put between two glass plates.
I'm wondering how much stress vacuum creates on glass plates and is cheap 2 mm or 3 mm glass plaet enough for euro card size?
I have small quiet compressor that has vacuum inlet. Might consider vacuum. There must be some stuff I'm not aware of.
Would it be possibe to use exact same thickness (probably easiest to use even same PCB material) as a "frame" that has eurocard (100*160 mm) or such cutout for the PCB under construction. Maybe neoprene seal on perimeter to seal the artwork - or glass plate?
Pekka
PK:
:doh:
--- Quote from: PekkaNF on January 24, 2016, 12:33:48 PM ---One more distraction: How does the vacuum system works on two sided UV PCB exposure unit?
I only have used method were PCB is slipped in a artwork and put between two glass plates.
I'm wondering how much stress vacuum creates on glass plates and is cheap 2 mm or 3 mm glass plaet enough for euro card size?
I have small quiet compressor that has vacuum inlet. Might consider vacuum. There must be some stuff I'm not aware of.
--- End quote ---
Vacuum is easily substituted with mass for the DIY case. You just need to hold the transparency onto the PCB. Holding it stupid hard doesn't (in my experience) make any difference.
The lid on my exposure box weighed maybe 6-7Kg. I used 5mm toughened glass, about 450mmx250mm. I recall supporting it at the ends with two bits of round bar and standing in the middle. Unbelievably strong stuff!
PK
PekkaNF:
--- Quote from: PK on January 24, 2016, 05:33:58 PM --- :doh:
--- Quote from: PekkaNF on January 24, 2016, 12:33:48 PM ---One more distraction: How does the vacuum system works on two sided UV PCB exposure unit?
I only have used method were PCB is slipped in a artwork and put between two glass plates.
I'm wondering how much stress vacuum creates on glass plates and is cheap 2 mm or 3 mm glass plaet enough for euro card size?
I have small quiet compressor that has vacuum inlet. Might consider vacuum. There must be some stuff I'm not aware of.
--- End quote ---
Vacuum is easily substituted with mass for the DIY case. You just need to hold the transparency onto the PCB. Holding it stupid hard doesn't (in my experience) make any difference.
The lid on my exposure box weighed maybe 6-7Kg. I used 5mm toughened glass, about 450mmx250mm. I recall supporting it at the ends with two bits of round bar and standing in the middle. Unbelievably strong stuff!
PK
--- End quote ---
Jep. I just wonder:
* Previously I had trouble finding material that will not absorb UV (surpricingly many glass and PMMA sheets does..) and like to keep it thin. Found 2 mm picture frame glass, this does not take much load.
* Taking care to put "ink" side next to photoresis, hmmm. not extremely flat if loaded only on edges...
* Would like to expose it two sided - one go - putting books or weight lifters on top of it is not viable
* Plastic C-profile seems to clamp it good enough, might go for that.
Usually KISS is best, sometimes it just takes few tries to get there and boil it down to minimum. :lol:
Pekka
PK:
Honestly?
You're overthinking it.
I ran 5mm glass and my exposure times were bang on for the wavelength (ie around 90 seconds) .
The plastic film and the copper layer crushes more than good glass bends.
That box that I showed a picture of (which had slotted mounts for the hinges BTW so the top plate of glass could always be parallel with the bottom) made hundreds and hundreds of boards with 10 mil tracks.
By all means, go buy special glass, vacuum pumps and dilthium crystals, it's fun to make these things as flash as you can (I'm serious, I really get it..).... but getting your dev/rinse/etch chemistry under control, or a temperature controlled storage box for chemicals and emulsion coated boards will have orders of magnitude more effect on the finished board than a few microns of gap between a film and a board.
PekkaNF:
Ok. Thank you. My suspicion has a reason: Few years ago I bough 1 metre long 5 mm thick PMMA (acrylic) that was supposed to transparent to UV. It Blocked most of it. When I asked them to double check it with BIG LETTERS, I got the type an sure enough it had a filter added....they refused to deliver small amount "stadard" PMMA that would not filter UV, noobody-wants-it!. Then I bough some "good glass" and you may guess it. IT HAD UV FILTER TOO. Fool me once - well - fool me six times?
I put presensitized PCB and different "transparent" material on both sides and nothing in 10 mm space between the glass and PMMA. That way I figured that while 30 s exposure showed up almost good eneough without any "filter" 120 s was marginal on that first UV-transparent acrylic sheet I got and the "glass" need nearly same. I had cut the acrylic to size and I was in process of finishing the light box.
I'll build slap together 2 sided unit that assumes sandwich of max. 2-classes (2-3 mm), two transparencies and PCB of 0,6 - 1,5 mm + plastic C-profile to keep them clamped. If that doesn't work I'll take up on knitting.
Pekka
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