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