Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "lcdpublishing" 
<lcdpublishing@...> wrote:
>
> 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.  

It's been mentioned before, but I'll say it again: there is no way to 
consitantly get perfect transfers with an iron. I would blame the 
un-evenness of the iron itself, combined with the steam holes, more  
than the PCB. The GBC Creative 9" laminator from Staples is only $50, 
$40 if you wait for it to go on sale. The rollers are rubber 
coated, so that even if the board has slight un-evenness, it will 
still get consistent pressure. This won't, however, do .064" boards, 
according to pulsar.gs, only .032". The HT210 will with modification, 
but it's about 3x more expensive. I have had perfect transfers ever 
since I switched, with both Press'n'Peel Blue, and toner on glossy 
laser paper.

Having said that, there are a few suggestions to make the iron work 
better. Initial board prep is important, but I think that some of the 
methods used here are overkill. I have always had perfect transfers 
by sanding with 1000 grit sandpaper (I think scotch bright is /too/ 
rough, and steel wool will leave oil), wiping it down once with 91% 
isopropyl alcohol, then wiping down with another clean paper towel 
once the dust from the sanding is removed. Use Bounty 'Glass' paper 
towels, as they don't leave residue like some other ones I've tried 
do. I used an iron with P'n'P for a long time before the laminators 
were available cheaply. A lot of the problem is air being trapped 
under whatever you're ironing (and sealed in by the traces), keeping 
it from transferring. Cut slits in the pattern where there's no toner 
with an X-acto knife in order to let more air out while you're 
ironing. Find an iron that has a /really/ flat bottom, I've found that 
cheap or travel irons tend to be 'flatter' than the more expensive 
models. The White Westinghouse iron I have has to be used on the 
Polyester mode...while the iron I used before it I put up all the way 
(as I've seen it often suggested to use irons on the highest temp), 
this one will burn paper or melt press'n'peel at anything higher than 
this. So test it before using it on anything important. Also, start 
from one edge of the board, and get about half an inch 'stuck' to the 
metal. Keep the other end of the transfer sheet held up and slowly 
work from one side to the other, this will also help prevent trapped 
air.
 
> 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.

If you are etching face-down in the etchant (which I reccomend as 
etching 'sideways' tends to create a more un-even etch, most of the 
time I have seen that it etches faster higher up on the board so that 
the top half will be 'done' while the bottom half will still have 
copper - rotate the board to prevent this), then you need to make sure 
there are no air bubbles trapped against it - I had this problem occur 
randomly and am pretty sure that's what caused it. Shake it every so 
often while etching to make sure the gas produced isn't trapped there. 
The holder I use to keep the boards or brass upside-down is tilted 
just a little so that air will hopefully go to the side, off of the 
project. Even if it's completely sideways, I've seen bubbles 'stick' 
to it, preventing etching. However, sometimes I have found no reason 
for this to occur, I suspect there is some contamination of the board 
or even possibly a section where the copper (or brass) itself has 
contamination, creating an alloy that isn't as easy to etch. I am 
going to start wiping it down with 91% isopropyl before etching to see 
if it stops doing it, hopefully this will not remove or soften the 
toner. 

> 
> 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.

One more reason to get a laminator rather than sticking with the 
iron... eventually you'll get frustrated. I got /very/ good at 
transferring with press'n'peel and I'd /still/ wind up having to 
re-draw lines every so often, it's just too difficult to maintain the 
steady, strong pressure that the laminator can. But even the laminator 
won't deal with big dents or other defects. And if you're doing thick 
boards, a laminator is still expensive...