Homebrew PCBs

wheedal99 wrote:

> --- In Homebrew_PCBs@yahoogroups.com, Russell Shaw <rjshaw@i...> 
> wrote:
>>Try doing a whole board. I've never got all the pads or tracks to
>>stick, and i even made special heated press from 5/8" aluminium 
>> slabs to get even pressure and temperature control. The other problem is
>>that the pressure can cause tracks to be flattened which makes them
>>spread wider causing ragged edges and shorts.

 > I'm not sure what you mean by a "whole board".  Almost everything I
 > do is under 6"x6".  Anything larger, or more complicated I send out.
 > Ordering boards is fairly inexpensive these days so the only reason I
 > do some of them myself is to save time.  What were you trying to do
 > that didn't work?

I was trying to get the normal laser printer toner-transfer system to
work for 'normal' 10cm x 10cm PCBs. I was using TTS paper that has a
gelatine coating that dissolves in water. The proper fuser thing costs
US$200 (~AUS$300 then plus postage overseas) so i made my own. I got
a 2.4kW spiral stove element and fastened it to a 30cm x 40cm x 16mm
slab of aluminium. I made a triac control with temperature feedback.
I had a second slab with insulated handle that sits on top. I let the
whole lot preheat before putting the pcb between. I tried varying
temperature, pressure, and cleaning/degreasing the pcb in various
ways, but i would always get a couple of pads or tracks falling off
in the water. Pressing the pcb harder would make the toner stick
better, but then there'd always be some tracks or pads that increased
in area because the toner was flattened. Later, i tried just lasering
onto transparencies, but you could easily say light thru the large
black areas and the resolution was not sharp. Printers were HP laserjet-II
and HP 4M+.

I then experimented with canon, HP, and epson inkjets using
genuine inks and transparencies. The epson stylus color was miles ahead
because they had transparency that absorbs the ink into a flat surface.
Large black areas have not a single pinhole and edges are sharp.
The other printers had "sandpapery" rough transparency that relied on
mechanical adhesion rather than chemical compatibility. They had rougher
edges, pinholing, and took much longer to dry. From what i found,
thermal heads seem to clog more than piezo heads, unless crappy refill
ink is used (anecdotal evidence). IIRC, some printers like HP have the
head built into the cartridge. Epson heads are part of the printer and
the cartridge is only a container.

It was ~5 years ago, and i haven't tried lexmark inkjets or newer
lasers. Lasers are probably better now, and are worth using if you
already have one and its resolution and contrast is *adequate*.
There are many very cheap inkjets and lasers on ebay.

One thing to beware of: with inkjets, after the ink is dried, it can
still be outgassing a vapour that wrecks photoresist that doesn't
have the plastic sheet layer. This happens with the epson transparency
and PRP spray-on resist. To fix, put the printout in front of a fan
heater for 10-15mins before using. It is very important to fully degrease
the copper before spraying with PRP. Vinegar with lots of salt works well.