Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "lcdpublishing" 
<lcdpublishing@y...> wrote:
>
> This weekend I etched some boards with .010" wide traces 
with .010" 
> wide spacing. After etching I found a couple of traces "broken" so 
I 
> had to repair them and with these old eyes, it wasn't easy but I 
did 
> get it.

For tiny breaks, I'm using a conductive pen.  It's silver particles 
in a carrier.  Supposedly you can simply draw traces, but I've found 
that it dispenses too much "ink".  What I do is put a blob on 
something handy (scrap PCB, etc) and use a toothpick or needle to 
transfer small amounts to the broken trace.  I've never tried to 
solder to a patch (it says it's solderable).  Resistance is 0.1 ohm-
cm when cured at 25C and 0.02 when cured at 150C.

You can get info from Jameco Electronics - 
http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?
langId=-1&storeId=10001&catalogId=10001&productId=263716

> As to the reason for the breaks in the traces - just being in too 
> much of a hurry.  After doing the toner transfer, I inspected the 
> boards very good and did notice the missing toner.  Knowing that 
the 
> Sharpie pen is too blunt to patch the spot, I just went for the 
> etching.  I really should have cleaned the boards and tried the 
> transfer process again - it would have been much faster and easier.

For cases like this, I use an eraser shield (anyone old enough to 
have drafted schematics and mechanical drawings by hand will know 
what this is).  If the eraser shield openings are too large, I use a 
piece of overhead transparency to reduce the opening.

I've found that the "original" fine point Sharpies work better as an 
etch resist.  The ink in the ultrafine is pretty useless.  I bought 
an industrial Sharpie with a wide tip to see if that ink is better.

For cases where too much ink get's applied, I use an eraser shield 
and eraser to remove the excess.  Anyone old enough to have drafted 
schematics or mechanical drawings by hand will know what this is.  
It took trips to a dozen office supply and craft places to find 
them; and the new ones are crap.  For cases where the eraser shield 
openings are too large, I use a piece of overhead transparency or 
similar material to reduce the opening.  In the end, I have nice 
straight edges...

I've got my toner transfer process down pretty well and don't 
usually have problems with traces being etched open.  I usually err 
on the conservative side and melt the toner until it starts 
spreading.  This can create shorts which I clean up with an Xacto 
knife before etching.  I always go over my copper fills to minimize 
pitting during etch.

Regards,
Dennis