On Tue, 26 Jan 2010, jcarlosmor wrote:
> No, EPROM erasers do not work with the spectrum of liquid, dry-film, and
> pre-sensitized PCBs.
There goes that bright idea.
> You do not explain exactly why are you going to do things "Right Way".
> If you only need a hobby PCB once a week you could do things same as you
> do now. If you want to do one (or 100) professional PCBs in the same
> week, maybe with real soldermask, you will need a good UV imaging
> exposure box. So the first thing is to avoid all those new fancy UV LEDs
> units. The reason is simple: no professional PCB shop use that. Period.
> You only have two alternatives, high-pressure mercury lamp, which is a
> hassle to operate when you only intend to image a single PCB, since you
> have to wait until UV energy become estable, or flourescent tubes, which
> is very simple and efficient to work on.
By the Right Way, I mean to have a mostly self-contained kit of equipment
that's simple, effective, and not fiddly. Fluorescent tubes seemed like
the best approach from a simplicity perspective. UV LEDs seem harder to
diffuse. The sort of box I'm considering goes something like this:
Two shells, each 4 inches deep with UVA fluorescent tubes in their
bottoms. These are fastened together with a piano hinge. A lip just
inside the edges of the shells holds a .25" glass slab upon which the
pouched stencil with PCB inside is placed. Strips of scrap PCB lightly
sprayed with rubber paint are laid along the edges and another glass slab
is laid on top. Once the top glass is laid down, it weight against the
scraps should prevent movement. Close the lid and latch. Rubber coating
on the shell lips tightly clamp the whole thing together. The thickness
of the glass prevents significant bowing.
> Also, you will need real vacuum if you want perfect results every time.
> You could built that at very low-cost with a modified fridge compressor.
> And you will need to CNC-machining some kind of fixture for registry of
> your PCBs fast.
I'm told that taping the stencils face-to-face to create a pouch makes for
good registration. Any opinions on this?
> I know that maybe all of this sounds excessive for doing a few PCBs, but
> it is the only way to do it "Right Way". Any other way you could end
> frustrated re-inventing the wheel.
What I'm after right now is a light box that exposes two sides at the same
time, is relatively inexpensive, and convenient to quickly pack up and
stick on a shelf when I'm done.
--
David Griffith
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