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I made another attempt at doing a PCB with the UV exposure method except this time, I added two transparency sheets on top of the artwork and the lazer printer toner of the artwork touching the presensitized PCB board. The good part is the entire design appeared this time, but as I was assembling components, I had to drill larger holes just to get most of the components to fit, yet I was using standard eagle libraries to insert the components onto my circuit before printout, and I also printed at normal 1:1 scale.

I came across one website mentioning about using a vacuum to suck the air out between the PCB and the circuit board for better contact.

At first I was thinking placing the entire PCB in a clear plastic sandwich bag and tape it up to a household vacuum and leave the vacuum running for the entire exposure time, but that would give my family grief as well as raise electricity costs.

Does a tiny vacuum (and/or relevant parts) strictly for the purpose I mention exist for the general public to use? If so, what's the technical name for it?

I'm just sick of my PCB production going wrong all the time and I feel if I can get the artwork to go 100% flat to the PCB with zero light shining in the wrong places then I'll buy the necessary equipment.

update

Would heat shrink wrap bags work?

I remember heat-shrinking the shrink wrap on my windows in my house back in the day to keep the cold air out and I ran over the wrap with a hair blow-dryer for a good 20 minutes and the wrap produced a really tight seal on the windows. I see that ebay sells heat shrink-wrap bags in small sizes that can fit my circuit board as well as my multi-function printer transparency (bought from Staples office store). The question is, would this approach work? or would the blow-dryer melt the transparency and/or screw up any part of the circuit board (especially the photo-resist layer)?

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    \$\begingroup\$ Have you considered having them manufactured? Companies like pcbway do small prototype runs (minimum of 5) very quickly for very low cost. It will cost less than buying the equipment to do it well yourself and the quality will be orders of magnitude better. \$\endgroup\$
    – vofa
    Commented Dec 23, 2016 at 0:50
  • \$\begingroup\$ Wouldn't a FoodSaver work? \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Commented Dec 23, 2016 at 0:52
  • \$\begingroup\$ I'll look into it but I hope it doesn't make any part of the pcb bad (including causing warping or doing something bad to the photo resist layer etc) \$\endgroup\$
    – user116345
    Commented Dec 23, 2016 at 1:19
  • \$\begingroup\$ @vofa, yes. Since I will be doing the same circuit multiple times, I want to do the first one myself to make sure everything works rather than have a board house do it only to find out that I made a bad connection \$\endgroup\$
    – user116345
    Commented Dec 23, 2016 at 3:37
  • \$\begingroup\$ Also, see my question for an update since I presented an idea. I just won't know if it will work 100% \$\endgroup\$
    – user116345
    Commented Dec 23, 2016 at 3:41

3 Answers 3

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Get a broken flatbed document scanner for cheap. The glass in scanners is UV-transparent. Extract glass from scanner and use it to weigh down your transparency film during exposure.

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I think you mean a vacuum press.

But I don't think you need to resort to that. And there's other issues I think you might be missing:

  1. There is no way that board etching affects the drilled hole size. It sounds like you are eyeballing the holes etched into the pads and then picking the drill bit based on eyeballing. Don't do that. Go into Eagle and read what hole size is used and use that drill size or slightly bigger for that pad. Or generate an Excellon drill file and use GerbV view it graphically. You can right click and get the hole size.

  2. Many plastics will block UV and require longer exposure times. Why not find a piece of sturdy glass and use its weight to press the negative to the PC board? Perhaps put a sheet of foam behind the PC board to make sure it is pressed evenly to the glass.

  3. Consider getting it manufactured in China. I use allpcb.com and seeedstudio.com and been happy with the results. I just got 5 pcs 2-layer boards maybe 1" x 2" cost $8 with $19 shipping and only took a week. Another design was just under 6" x 2" and 5 pcs cost $14 + $17 shipping.

At home, I've got the laser toner etching method worked out pretty good, but unless I'm in a super hurry, I would rather pay a bit and wait a week to get a professional board, 2 layers, silkscreen, soldermask, and fine geometry and save the time and hassle.

Hope that helps, -Vince

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  • \$\begingroup\$ For point #1. I use 1/32 inch drill bit for all my boards. In the past when I did my smaller boards (2inx2in), that drill worked perfectly and the IC's fit perfectly. I seem to have difficulty with larger boards. For #2, I used a picture frame to secure the artwork to the board with 4 included picture frame clamps (1 on each side). This works for small boards but not for large ones. and I'm going for option #3 when my first board is a success. Thanks for the help though. \$\endgroup\$
    – user116345
    Commented Dec 23, 2016 at 5:33
  • \$\begingroup\$ For #2, I suspect the middle of the board might have a gap since you are only clamping the edges, hence the idea of a foam sheet behind the PC board to make sure the middle of the board is also pressed against the glass. \$\endgroup\$
    – Vince Patron
    Commented Dec 23, 2016 at 5:41
  • \$\begingroup\$ For #1, you might want to use some digital calipers and make sure the hole spacing is correct, and measure some larger distance like an inch or few inches and compare against Eagle. Some printers you have to print "Actual Size" to make sure it doesn't slightly reduce the print to fit within printable margins. \$\endgroup\$
    – Vince Patron
    Commented Dec 23, 2016 at 5:43
  • \$\begingroup\$ Oh foam sheets is an idea \$\endgroup\$
    – user116345
    Commented Dec 23, 2016 at 15:13
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You are looking for a machine like this: http://bungard.de/index.php/en/products/exposure-units/hellas

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