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Best Low-Cost Home PCB Prototyping?

Discussion in 'PCB Layout, Design and Manufacture' started by Johnyradio, Nov 17, 2017.

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  1. Johnyradio

    Johnyradio

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    Oct 30, 2012
    @(*steve*) , really appreciate you sharing crucial gotchas. i think these are your 2 main gotchas, both related to SMD's:
    • Chemical Etching: undercutting.
      • Caused by over-etching, correct?
      • Fixed by sponge method, plus maybe drawing traces slightly thin. No?
    • Milling: Ripping the copper.
      • Caused by warped or non-level board-surface, correct?
        • "the problem with V-bits is that you need pcb surface to be extremely flat" reply #11
      • Question: Is non-level surface caused by non-level platform, or varying thickness of the PCB?
      • Warping fixed by bolting the board down on all sides to a non-warpable platform. No?
      • Uneven surface fixed by bolting the board down on all sides to a level platform, plus software compensation. No?
      • Further helped by use of tear-resistant bit, such as this one.
        • "Optimized for trace isolation and copper rubout on printed circuit boards. 15° taper angle minimizes cut width variation due to poor substrate flatness"
    Paint? Your comment below sounds like you mean laser-cutting the copper, not milling the paint. Confused.


    check out PreciseBits link above.

    Ok, so you're agreeing we can reduce undercutting by not sponging the already-etched areas. Correct?

    Yep, as mentioned in my OP, "most inkjet methods i've seen are too fiddly, finicky, and/or sloppy)."

    A UV box or laser cutter seems superior to messing around with magazine pages and a laminator or clothes iron. No?
     
    Last edited: Nov 18, 2017
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    You need to do more research. Toner transfer does not involve an inkjet printer.

    The laser method removes the resist from the board (I use high temperature paint) . The board is then chemically etched.

    etching removes exposed copper. As it removes copper some edges are exposed. These are also etched. In effect the minimum amount of undercut is the thickness of the copper. In practice it's more.

    I'm not an expert on milling.
     
  3. Johnyradio

    Johnyradio

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    Oct 30, 2012
    i've only seen toner-transfer methods involving either an inkjet printer or a laser printer, plus a laminator or clothes iron.

    https://www.instructables.com/id/Cheap-and-Easy-Toner-Transfer-for-PCB-Making/

    https://hackaday.com/2016/09/12/take-your-pcbs-from-good-to-great-toner-transfer/

    (what i don't want to do)
    [​IMG]

    Can you share the non-printer toner transfer methods you mean?

    Yes, i understand that. I listed it in my OP: "Laser cutter: remove resist"

    i know.

    Wow! i didn't know that! So, if the vertical cross-section of the copper is, say, .7mil thick, then the undercut will cut .7mil depth horizontally into the copper? Any idea why?

    You're clearly more experienced than me! i've only used an OtherMill (now Bantam) a few times.

    Would be great if you could comment on my suggestions above on how to reduce undercutting.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Mathematics.

    Also toner transfer doesn't use an inkjet printer because inkjet printers don't use toner.
     
  5. Johnyradio

    Johnyradio

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    Oct 30, 2012
    very cool, can you share the math? i researched a bit, could not find anything.

    Thanks for the correction. My misunderstanding, my bad. Don't be mad.

    ---------

    method of interest:
    Not commercially available yet.
    http://printem.io/
    https://hackaday.io/project/13270-printem-instant-printed-circuit-boards
    [​IMG]

    ---------
    This article mentions something called Laser cutting "edge etching." Any idea what that might be?
     
    Last edited: Nov 18, 2017
  6. Johnyradio

    Johnyradio

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    Oct 30, 2012
    my current preferred method: This inkjet/UV method, using transparencies (also reported to work with a normal fluorescent bulb). Seems much cleaner and nicer than messing with a laser printer, ripped-out magazine pages, and a clothes iron. :)

    + sponge: sponge-etching seems the way to go:
    • consumes less consumables
    • handling much less quantity of toxic chemicals in an open container.
    • throw less gunk into the environment
    • faster
    • small setup. No tanks, bubblers, or heaters
    • "Undercutting is practically non-existent"
     
  7. kellys_eye

    kellys_eye

    4,276
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    Jun 25, 2010
    I use the '
    I use the 'shiny' backing paper left over from adhesive stickers (the backing) - laser toner can almost (in fact quite easily) be wiped off with the finger such is its non-adhesive quality. It retains enough stickiness to get the toner where it's needed though.

    And I then use a simple laminating machine (used to laminate paper in plastic) to apply the heat. This process has worked flawlessly for me for a number of years, is cheap, repeatable and clean.

    I also use the UV method but am 'too cheap' to reliably purchase stocks of pre-sensitized boards and have had too many failures with spray-on resists.

    My ideal method - if I could be bothered to progress it - would be to cover a copper board in the same black stuff that is used in old fax machines (dry printing) using a thermal roller (laminating machine) then exposing it to a suitable laser scanning process (per laser printer but 'open air and flat') to burn off the areas to be etched.

    I've also looked at applying that dry print process directly but have had zero success in finding a thermal print head that has a flat thru-path - they all have a 'ridge' that paper can pass over but stiff pcb material can't.

    Other DIY methods I've looked at used flat bed scanner mechanisms and direct-to-board printing using dry ribbon, the latter method worked well but the printer and supplies were obsolete even then - I eventually sold the printer and what supplies I had remaining for 30x what I paid for it!
     
    Johnyradio likes this.
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Read this.

    Note on slide 4: "etching always result in undercuts"
     
  9. Johnyradio

    Johnyradio

    34
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    Oct 30, 2012
    Undercutting:

    Thx for that. Clearly there's got to be some undercutting. No doubt the above claim i quoted, "undercutting is practically non-existent" with sponge method can't be completely true. What's more likely is, it reduces undercutting to an acceptable level (prolly with practice-- any method improves with practice :)

    Note, the article you linked says there's some ratio between copper thickness and amount of undercutting, and it's called "etch factor". But they don't mention any fixed ratio, they just advise to keep it as low as possible.


    Photoresist

    Seems there's only photosensitive film on ebay, which has to be adhered to the board with a laminator or iron. And i thought i was getting away from the ironing board :/

    About the spray-on resist you mentioned. This page says:
    Is that the issue you had? i imagine it might also be difficult to get an even coat.

    This method is based on brushed on paint, instead of spraypaint. Thoughts?


    Toner Resist
    If you're happy with your toner-resist method, why are you looking to change?

    cheers
     
  10. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Johnyradio likes this.
  11. Johnyradio

    Johnyradio

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    Oct 30, 2012
    Last edited: Nov 19, 2017
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,401
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    Jan 21, 2010
    A colleague of mine used pre-sensitised board and laser printer output. Now he has built a machine to apply the resist film to the board directly.

    Be careful with the life of pre-sensitised board. Some has a very long shelf life, other stuff needs to be used quite quickly.
     
  13. Johnyradio

    Johnyradio

    34
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    Oct 30, 2012
    :eek:
    A specialized laminator?

    Thx for tip! it happens i have some presensitized boards that are a couple yrs old o_O
     
  14. Johnyradio

    Johnyradio

    34
    0
    Oct 30, 2012
    Something like this?

    Seems a very clever method. "Draw" resist on a presensitized board using a laser. Then you don't have to print the art to a transparency. Still, seems would take more time overall, compared to exposing the whole board in one go.

    That site has several DIY mill designs, btw.
     
    Last edited: Nov 19, 2017
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