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Accuracy and procedure for home-made PCBs

Discussion in 'PCB Layout, Design and Manufacture' started by TTL, Oct 14, 2015.

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  1. TTL

    TTL

    187
    5
    Oct 24, 2013
    I'm about to have some home-made PCBs sourced from 1980s electronics magazines but am concerned about the resulting quality and what I can do about it.

    The PCB layouts have all been scanned from magazines at a high (1200 DPI) resolution, then meticulously touched up in Photoshop (spots and dust removed, imperfections fixed and all traces overlaid with 100% black instead of keeping the traces dark gray as they became when they were first scanned). But as they were obviously not computer generated but rather hand-drawn to begin with they're not of the same quality you'd get nowadays. So what's "good enough" in order to get a working PCB (without broken traces etc.)? I've also made reduced (300 DPI) versions from the original 1200 DPI scans and the resulting prints don't seem to differ that much.

    Someone else is going to do the actual transfer and etching while I'm in charge of the scans and printing to transparencies using my laser printer at the highest possible output quality. He has access to a large UV light, press'n peel, etchant etc. so there are various options we could try out.

    I've read that it's advisable to print two identical sheets and put them on top of each other to get close to 100% blocking of the UV light where the circuit traces are, but the guy who's doing the UV-lighting and etching tells me he's had bad experience with shadows using an additional sheet.

    So is there anything else I can do apart from the above? Do I need to retouch further so that all jagged lines become 100% straight for instance or will the source material do? Anything else to keep in mind?
    Below is one of the PCBs (reduced size) along with 100% of sections in 300 and 1200 DPI.

    PCB overview (reduced size):
    pcb reduced.png

    100% (1200 DPI) section of PCB (you might have to click on it here in order to actually view it in 100%):
    1200ppi at 100.png



    100% (300 DPI) section of PCB (you might have to click on it here in order to actually view it in 100%):
    300ppi at 100.png
     
    Last edited: Oct 14, 2015
  2. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    As long as there are no breaks and traces have adequate separation, the PCB will be functional. I would also check the scaling to make sure your .1 inch pin spacing is correct.

    Bob
     
    Last edited: Oct 15, 2015
  3. TTL

    TTL

    187
    5
    Oct 24, 2013
    So from the above examples you'd say the PCB layout looks OK to use?
    I'll check the scaling by placing the actual components on top of the printout to see if they match.

    How about using two layers of transparency sheets (in order to get complete blockage of the UV light) -do you have any experience with that and have avoided getting shadows because of the increased thickness?
     
  4. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    Yes, I think they are OK to use. I have never used 2 transparencies and have never had a problem. You might want to up the density on your laser printer, but that might cause traces to swell a bit.

    Bob
     
  5. wrighty

    wrighty

    10
    0
    Aug 1, 2009
    I would be seriously thinking about inputting the schematic into a CAD program and then creating a new pcb.
    You will end up with a much better result.
     
  6. NicolasK

    NicolasK

    1
    0
    Oct 26, 2015
    With UV light and other small tools, constructing a homemade circuit board is a relatively simple task these days. here is an article you might want to take a look. http://www.syspcb.com/News/319.htm
     
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