[chbot] Anyone making PCBs?

[Andrew Errington]

On Sat, 04 Jun 2011 13:32:18 Volker Kuhlmann wrote:
> On Wed 01 Jun 2011 16:26:27 NZST +1200, Andrew Errington wrote:
> > Yes, I tried that, but I didn't have good adhesion, so the tracks came
> > off too.  I think the key is very clean copper.
>
> Yes, that makes sense. Is it really necessary to remove all the last bit
> of copper oxide, and to use acetone? Fingerprints will be a k.o., but
> they come off with meths. Did you by chance try it with meths insted of
> acetone?

No, sorry.  I happened to have acetone in the form of nail varnish remover, 
and it's what most people were recommending so I used it.  I have some meths, 
so I could try it.  I am sure it will be okay for cleaning the board, but I 
am not sure it will dissolve toner (for bad transfers or to clean the board 
after etching).  I will report back about this.

I expect the eventual success was caused by using the same piece of board for 
about three failures.  Each time I had to wipe the toner off and scrub the 
board again, so each time it was getting cleaner and cleaner.

> The other bit of info I'd be interested in is what size structures can
> you reliably etch with this method?

I don't know.  I have seen some 'test patterns' on the web with various 
track/gap sizes to evaluate the accuracy, but I never tried them.  My tracks 
are 0.017" wide on a 0.025" grid, and I flooded the ground plane with 0.010" 
clearance to adjacent tracks/pads.  It etched ok.  There is probably a DIY 
report somewhere on the web documenting what works, and you can probably 
accept what is reported as true (even if it is some guy on the Internet whom 
you've never met).

> How long does the toner on the copper withstand the acid? The problem
> with photo-resist-plated board was not usually the resolution, but the
> etching damaging the photo-resist layer before all the unwanted copper
> was dissolved.

It seemed to me that the toner layer itself was unaffected by the acid but I 
didn't really look.  If it adheres well then it's actually quite robust.  It 
can be scrubbed with a soft toothbrush, and is even resilient to a fingernail 
scraping the edge.  On my first board I had to touch up some non-adhered 
toner with a Sharpie (you probably know Sharpie permanent ink works as 
etch-resist).

For a long time I had been wanting to try it, but I can attest that the 
reports from others are true.  It's a finicky process, but it's dirt cheap, 
and it works.  I suggest you have a go at the first part, toner transfer, if 
for no other reason you want to verify it for yourself.  You could use any 
artwork, even some text, if you don't have a PCB in mind right now.  Be aware 
that some brands of toner perform differently to others, but I used whatever 
was to hand, which was a Fuji Xerox printer with (probably) an OEM toner 
cartridge.

I wouldn't recommend this for any sort of commercial activity, but it would be 
great for prototyping, and is perfect for hobbyists.

Andrew