Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "mikeromp2002" <MikeRomp@m...> 
wrote:

> Personally, with soldering a scrap piece of wire, or using one of 
the 
> other discussed via methods being so easy (and repairable) I will 
not 
> be spending the money on the paint.  Remember, when paint dries it 
> tends to become brittle and possibly even crack with heat. I guess 
if 
> it really worked that good/reliably, the "big boys" would be using 
> something like that on the professional boards. Just a thought.
> 
> Keep us posted if you decide to try it.
> Mike R.

It looks like I'm going to be the one to save up £6 and nip down
to Maplins some time (Farnell, RS etc are the same price). Quite a 
few people seem to have success using it for bridging clock divider 
pins on AMD processors, so I imagine thermal cycling (and fairly high 
temperature) isn't a problem for the modern stuff. In fact, according 
to the data sheets it seems that curing it at 85deg C or so gives a 
lower resistance.

I intend to use several thinned applications of paint, followed by a 
coating of something to stop the oxygen attacking it. The idea is to 
be able to connect up layers on a laminated board (initially 3 layer, 
1 double sided bonded to 1 single sided). Using the wire method would 
take 2 vias, the first to connect the 2 sides of the double sided 
(and thoroughly smoothed off), then another to connect the 2 outer 
layers. A blind via from inner to the outer of the single sided board 
wouldn't be possible with wire. 

The hope is that maybe I can get connection density high enough to 
support BGA packages, where there just isn't room for wired jumper 
vias. My motivation is that I have a device that I really would like 
to use but is only available in BGA, and increasingly the interesting 
stuff has no alternative (ARM processors, memory, high speed ADCs 
etc).

All I need now is a free source of 0.4mm copperclad to experiment 
with!

Mike