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How good is YOUR etching process?

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ragnar

Wed Nov 21 2007, 04:18AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
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Posts: 1425

I make PCBs (predominantly for surface mount) very often now, and I've got my process tuned down to a fine art. For a while I've conservatively used 16mil traces as standard for signal traces... but even then, sometimes things get tight, so I became curious how 'fine' my 'art' could be.

Below are three permutations of four different track widths. The first column has a 'pitch' of 50mil between traces, the second column has a pitch of 25mil between traces, and the third column has a pitch equal to the width of the traces (50% overall copper area, if you like).

My toner transfer medium is "Canon Color BJ Paper" (LC-201). I'm using it because I found several reams in a dumpster. My etchant of choice is boiling ammonium persulphate, and I nuke the board (face-down!) in a Corningware Vision glass pan on my gas stove. I print using the "1200dpi FastRes" setting on my flatmate's HP LaserJet 1020.

From these samples, it's clear that 8mil traces ARE possible -- a pleasant surprise. Clearly though, I must allow MORE than 8mil 'empty space' between traces -- the bottom-right-most photo shows the obvious limit to my process. The 25mil trackpitch is perfect.

Does anyone use press and peel? Milled boards? UV photoexposures? How good are your results?

16mil traces
50mil 25mil 32mil

12mil traces
50mil 25mil 24mil

10mil traces
50mil 25mil 20mil

8mil traces
50mil 25mil 16mil

nrhoades

Wed Nov 21 2007, 04:22AM

Registered Member #610 Joined: Wed Mar 28 2007, 09:44PM
Location: Middletown, RI
Posts: 110

Are you talking about just using toner? I could probably get very thin using different masks. I should try it. Expect a post soon.

...

Wed Nov 21 2007, 04:50AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

That is pretty good, about on par (a bit better actually) with what I get using the press-n-peel system

What copper thickness are you using?

The stuff I have been using is about 3 mills, which makes it quite tricky to get 8 mil traces withough major undercutting. See my GPS tracker boards...

Those big long traces are on a 10mil/10mil spacing

ShawnLG

Wed Nov 21 2007, 05:27AM

Registered Member #286 Joined: Mon Mar 06 2006, 04:52AM
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Posts: 399

That is a nice test Matt. I have finally purchaced a used Lexmark 1200*1200 DPI B&W laser printer for $20 a while ago just for this purpose. I have not done any PC work with it yet because the toner is too light when printing. I don't know if a new toner cartridge would solve the problem or not.

Hazmatt_(The Underdog)

Wed Nov 21 2007, 06:27AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

I usually use paint pens these days for quick boards and I don't have any overetch issues.

For fine boards I do UV exposure and that usually goes pretty well.

You do have nice boards Matt, but you still overetch.
You ought to take care of your agitation issue first, then you'll have it down to an art.

ragnar

Wed Nov 21 2007, 07:46AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
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Posts: 1425

Hazmatt_(The Underdog) wrote ...

You do have nice boards Matt, but you still overetch.

No, I etch only as long as necessary for the last of the unwanted copper to disappear off the board. I accept as a fact of life that cheap laser printers and thin traces may result in trivial undercutting.

wrote ...

You ought to take care of your agitation issue first, then you'll have it down to an art.

The board (actually, the entire pan) is hand-agitated as one would cook a stir-fry, which has given me these great results for 8mil traces.

Some 'spreading' of the toner does occur during the iron-on process (sometimes giving a gently undulating trace width), but this is expected.

Hazmatt_(The Underdog)

Wed Nov 21 2007, 08:50AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Trivial? dude, if 12mil were your company logo everyone would be pissed off.

I hand agitate too. Are you shining up your boards with steel wool before applying your trace? If not then I would start doing that, that would help with the peeling problem.

ragnar

Wed Nov 21 2007, 09:54AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
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Posts: 1425

Hazmatt_(The Underdog) wrote ...

Trivial? dude, if 12mil were your company logo everyone would be pissed off.

I use 600 grit sandpaper to prepare the surface of the copper. The legends were an afterthought, and outside the area I had treated with sandpaper.

I'm not asking you to critique my method, feel free to post your process.

Tom540

Wed Nov 21 2007, 03:20PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
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I used to use an ink jet printer to print mine and it worked really good. Only problem is some transparencies don't work and some do. I should post a pic when I get home.

Avalanche

Wed Nov 21 2007, 07:05PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

I also use an inkjet / UV exposure and I have managed to get down to 15 thou for SMT, with quite clean lines. Could go finer, but I've never needed to!

It goes something like this...

1 - Print onto 'Staples' own brand overhead transparencies, with the printer on the highest resolution and *important* set the printers media type to 'Premium photo paper' *not* 'overhead/transparency'. (Reason is if you select the transparency, the printer tries to be clever and apply the ink in a bizarre 'micro grid' pattern, presumably to stop it from flowing. It really doesn't need to do this, you get much sharper lines with it set to photo paper. This is on an HP deskjet, not sure if it applies to others.

2 - Cut the thing out let it dry etc etc apply to FR4 photoboard ink side to board and expose to UV from 2 computer cold cathode tubes for 8 minutes (I use a piece of glass from a picture frame, on two blocks of 1.5" square wood with the tubes underneath

3 - develop, etch - drop board into paint tray and throw in the end of a running electric tyre pump (can be a bit messy but it helps speed things up a bit

)

That's some pretty good results you managed with toner transfer though, you have lots more patience than me! I gave up with that long ago when I realised I could buy inkjet transparency.

I guess it doesn't even need to be transparency either, only transparent to UV...

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