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Best Low-Cost Home PCB Prototyping?

Johnyradio

Oct 30, 2012
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@(*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"
Yes, but the control, whilst sufficient for most normal tasks is not fine enough for ablating paint.
Paint? Your comment below sounds like you mean laser-cutting the copper, not milling the paint. Confused.

"a lower powered laser cutter with more software control could do the isolation milling..."
I imagine you could use a tool with parallel cutting edges, but you couldn't do fine lines then (and it would be far too easy to snap)
check out PreciseBits link above.

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

Have you considered toner transfer?
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?
 
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(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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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.
 

Johnyradio

Oct 30, 2012
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You need to do more research. Toner transfer does not involve an inkjet printer.
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)
yG2Uu6j.jpg


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

The laser method removes the resist....
Yes, i understand that. I listed it in my OP: "Laser cutter: remove resist"

etching removes exposed copper.
i know.

the minimum amount of undercut is the thickness of the copper.
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?

I'm not an expert on milling.
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.
 

Johnyradio

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

toner transfer doesn't use an inkjet printer because inkjet printers don't use toner.
Thanks for the correction. My misunderstanding, my bad. Don't be mad.

---------

method of interest:
The technique prints the PCB pattern onto a sheet of Printem film which is then exposed to light for around 30 seconds and then the top layer is peeled back to reveal the finished PCB, that’s it!
Not commercially available yet.
http://printem.io/
https://hackaday.io/project/13270-printem-instant-printed-circuit-boards
iJPb8YX.png


---------
This article mentions something called Laser cutting "edge etching." Any idea what that might be?
 
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Johnyradio

Oct 30, 2012
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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"
 

kellys_eye

Jun 25, 2010
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I use the '
Seems much cleaner and nicer than messing with a laser printer, ripped-out magazine pages, and a clothes iron.
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

Oct 30, 2012
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Undercutting:

Read this. Note on slide 4: "etching always result in undercuts"

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:
"It’s very hard to use, as you always get dust settling on the wet resist. I wouldn’t recommend it unless you have access to a very clean and ventilated area or drying oven, or only want to make low-resolution PCBs."
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
 

Johnyradio

Oct 30, 2012
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(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Tho laminating or painting my own might be significantly cheaper, precoated are likely better.

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.
 

Johnyradio

Oct 30, 2012
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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.
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.
 
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