Re: Printed Circuit Board Supplies

Ted Robbins wrote:

> From: Ted Robbins <rtr@...>
>
> >From: hansw <hansw@...>
> >
> >the same boards today are over $133 ! close to double price in 9
> >months...
> >
> >I looking for a different source, any recommendation, in the USA...
> Before I gave up trying to run a circuit shop in a "Green" community,
> I
> built them. I used screening techniques to do production, but I used
> photosensitized boards to do prototypes.

I use DuPont Riston dry film resist. Having tried a number of other
resists over the
years, I can say that nothing else comes close! The resist is almost as
tough as
a good solder mask! It takes a serious accident to scratch it, and it
is impervious
to hours of soaking in hot etchant. The developer is sodium carbonate,
a relative
of baking soda.

> I sensitized them with photosensitive polymers. They are available in
> both
> positive and negative working chemistries. The only real trick is to
> get
> the boars very clean. Water must sheet over it, not stand in drops.
> You
> can pour the sensitizer over the board in ordinary room light. I
> prefered
> incandescent to flourescent because flourescent contains a lot more
> UV.

The hot roll laminating of the dry film allows it to stick well to
boards that are less than
perfectly clean. I clean them as well as I can, but they still have a
few spots or slight
blemishes on them. The resist still sticks to the entire board, blemish
or not.
I use yellow incandescent bug lights, and turn off the fluorescents in
the area when
I'm working with these.

> Having said al that, I must add that I would never use a chemical
> process
> again. The paranoia of experience compels me to point out the legal
> danger
> you face when using chemicals. Technical illiterates saving their
> planet
> will make your life very difficult. I would route boards today, not
> because it is a good way to make a board, but because you could easily
> end
> up in jail using rather common and relatively innocuous reagents.

I don't ever want to use the KPR type process again, but I have no
qualms about
using dry film. The Fe2Cl3 etchant is pretty hard on skin, but I use
rubbermaid
gloves, and really have no problem with it. I'm using the same 3
gallons of etchant
I started out with 10 years ago (after I moved my shop) and it still is
going strong.
So, the chemical waste problem is not a big one. The routing process is
not
entirely clean, either, as you are making a LOT of fiberglass/epoxy
dust.

Jon