Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Hi Guys,

I etched a board the other day using some new PCB material I got. I
did the usual cleaning and polishing process that has been working
good for me. However, I did have some toner transfer problems - and
even etching problems on these PCBs.

The best I could determine is that the suface of the copper is very
slightly rippled - sort of like the threads in fabric - but more
course. This seems to be the cause of the toner transfer problem -
toner not sticking in these areas.

After etching, I also found that some small spots didn't etch all
the way through - ie. a dot of copper is left on the board. I am
guessing that this was a small void in the glass backing (FR4) and
when the copper was applied, it was thicker in the area of the
dimple - thus taking much longer to etch. Something like this, I
don't believe there is anything at all that can be done to correct
it so I am not too concerned at this time.

Howver, the toner transfer process seems to require that you have a
smooth and flat surface for good transfer and adhesion. If I had a
micro scope, or some such device, I would look much more closely at
the surface texture of the copper to validate this. With the naked
eye, or even a loupe, I can't really see much deformation on the
surface. I do suspect though, that even a deformation of .0001"
would be enough to cause problems.

When pressing the paper onto the PCB, I use a paper based shop towel
between the iron and the PCB to act as a pad and to also help
accomodate surface irregularities. However, I am going to look for
something that will work better.

I guess what I am saying is this. The next time you get "Missed
spots" with toner transfer, take a really close look at that area on
the copper to see if it is in fact flat and smooth.

Chris