Homebrew PCBs

Finally got around to testing the MG Chemicals negative dry film
resist.  I got a 5'x12" roll for $28 with shipping (shipping cost
almost as much as the film!)

Lamination: The MG instructions say to dry laminate it, which I did,
at 230F.  There were a few tiny bubbles, but no worse than I usually
get.  I might try a larger board to see if holding the film away from
the board reduces bubbles.

Exposure: 4 minutes in my exposure box (99x 395nm UV LEDs @20mA) holds
at 6 on an ST21 gauge.  This is less than the Riston film, so will
require more exposure time.  My LEDs are a bit outside the sweet spot
from the spec, but who knows.  The MG site doesn't spec exposure other
than "12 minutes with our unit", so I'm just guessing at the ideal
exposure time - I'll try a longer exposure with a photofilm pattern
under it to see what works best in practice.

Development: Despite MG claiming it won't work, sodium carbonate works
just fine, with development times about the same as the Riston film.

Quality: The film quality seems OK (not that I'm an expert).  There
are a couple of microscopic pinholes in the exposed parts, but that
might be my process.

Stripping: NaOH stripper works, but not the same way as Riston.  With
Riston, the film would swell and separate from the pcb so you could
see when it was time to take the board out and scrape off the waste
film.  With MG, the film turns into pudding but *looks* the same.  It
still scrapes off after the same amount of time, but it's harder to
tell when that time is just by looking at it.

Overall: The MG site is sorely lacking in specs and details on how to
use their film with anything other than their equipment, which is a
big negative.  However, it seems to work mostly the same as other
films, and is available in smaller units than Riston, although the
cost/ft is about twice as much.

DJ Delorie wrote:
> Exposure: 4 minutes in my exposure box (99x 395nm UV LEDs @20mA) holds
> at 6 on an ST21 gauge.  This is less than the Riston film, so will

Would I be right in thinking that the ST21 is the step gauge you mentioned in 
an earlier posting? Who makes them?

I've tried a quick Google search, but didn't find anything remotely useful...

Thanks,
-- 
Phil.
ygroups@...
http://www.philpem.me.uk/

Philip Pemberton <ygroups@...> writes:
> Would I be right in thinking that the ST21 is the step gauge you mentioned in 
> an earlier posting? Who makes them?

Yes.  http://www.stouffer.net/TransPage.htm

DJ Delorie wrote:
> Philip Pemberton <ygroups@...> writes:
>> Would I be right in thinking that the ST21 is the step gauge you mentioned in 
>> an earlier posting? Who makes them?
> 
> Yes.  http://www.stouffer.net/TransPage.htm

Hmm, they seem to be a bit thin on the ground over here... Most of the 
photography suppliers around here have (rightly or wrongly) abandoned the 
darkroom side of things.

Looks like RH Designs are selling them as add-ons for their darkroom timers 
and process monitors though: 
<http://www.rhdesigns.co.uk/darkroom/html/accessories1.html>

I've just ordered two -- will post again when they turn up.

-- 
Phil.
ygroups@...
http://www.philpem.me.uk/

Philip Pemberton <ygroups@...> writes:
> I've just ordered two -- will post again when they turn up.

Note that you don't need the calibrated ones ;-)

DJ Delorie wrote:
> Philip Pemberton <ygroups@...> writes:
>> I've just ordered two -- will post again when they turn up.
> 
> Note that you don't need the calibrated ones ;-)

I figured as much 8^)

Also got a PCB shear (one of the Mega ones), and a ton of other PCB stuff on 
order from Rapid. Cheaper than buying it all from Mega, anyway...

-- 
Phil.
ygroups@...
http://www.philpem.me.uk/