Homebrew PCBs

On Thu, 2009-09-03 at 09:44 +1000, Adam Seychell wrote:
> 
> The link below is of a board I did recently. I know its quite ugly,
> but 
> I'm only just learning about this solder mask stuff.
> http://members.optusnet.com.au/eseychell/revH_photo.jpg
> 
> I'd like to know what experience people have with dry film
> soldermasks. 
> Might be lot more practical for hobbyist.
> 

Adam,
Your first board with LPI soldermask looks really good. I would prefere
to buy boards from you than from some boardhouses out there. I used a
lot of dry film soldermask but i don't like it (neither riston) and
won't recommend it. It can seem a good option for the homebrew but the
LPI options out there seem even better and also easier to get.

Comparable to riston the vacrel (dry film soldermask from dupont) is
laminated at same 110�C, and developing time in Na2CO3 is also the same
along with temperature and concentration (same tank and procedure for
both, but increase time for never fail results), but exposure time on uv
lamps is about the double i used 10seconds for riston and 19s for
vacrel, on same vacuum exposure unit and same high contrast photoplotter
film. The cure was 2hours on 100W uv lamps, but should be less uv and
some oven heating. The lamination pressure should be superior to riston
but the expensive and far from good bungard laminator was already stupid
painful to operate.

I won't recommend it because:
* I really hate the smell of it. When heated has really nasty gases, not
even strong exhaustion ventilation remove the smell.
* Is very very difficult to laminate. I used a big very expensive (like
a good car) professional laminator that always laminate riston without
problems and still soldermask always had bubbles on it. 
* Is not a thing to put on a oven. That air bubbles can lift the
soldermask or your components when heated. The air bubbles are tricky
also in low pressure environments. 
* It gives a ugly very thick finish. Is so thick it looks like a pvc
sheet glued above like a stencil. 
* Hard to remove if a problem in application occurs. If you misalign the
artwork or over/under expose/develop, for example , you can only remove
it in 15min acetone dipping and scrubbing. After cure is impossible to
remove. 
* Is very expensive and hard to get. Any low quantity application method
of dry film has considerable wast, when using expensive dry film the
wast is a budget hole.

You know i am a big fan of your lamination method, after understanding
how a professional laminator works every laminator i can afford seems
just more trouble than results. But i don't know if your laminating
method will work good enough with dry film soldermask.

BTW, you should rename your method to 'Painless Dry film lamination
method for the homebrew (with water)' , wet lamination is spraying hot
water between the hot rubber roll and dry film to replace microscopic
air bubbles by water which will disappear in some hours because the
dryfilm is water soluble.