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Re: gEDA-user: photo-imagable supplies (was: dremel "drill press")

Hi,

   When I did double sided photoresist boards I used a frame made from aluminum. The frame was made from a rectangular piece of aluminum sheet that had the same thickness as the board that we were using. There was a large cutout in the middle of the sheet to allow the board to sit in there. Imagine what a matte for a picture frame looks like. The two masks were then taped one on each sides of the frame and were aligned by looking through them. One side was not taped all the way around so that you could lift it up and place the board in between them. Two sheets of glass were then placed one on each side, and held there with hose clamps. The resulting sandwich was then placed unde UV poster lamps to expose. First on one side, then the other. If we had more lamps we would probably have built a frame to expose both sides at once. 

With this setup I made quite a few ISA plug in cards for PC's. The only real problem I ran into was that occasionally the print shop that did my photomasks would use a different piece of glass to hold down my original, this different glass ended up making about a 2% difference in the output size. Unfortunately for me they did this randomly, and I would end up with top and bottom that did not align. After I got burned a couple of times, I added a vernier scale to the output plot, and showed them the error, and made them do it again until they got it right. The eventually figured it out, and after that they made real nice plots for me. 


--------------------------------------------------
                                      Mike Jarabek
         FPGA/ASIC Designer, DSP Firmware Designer
http://www.sentex.ca/~mjarabek                    
--------------------------------------------------  

-----Original Message-----
From: John Griessen <john@xxxxxxxxxxxxxx>
Date: Mon, 16 Apr 2007 10:05:19 
To:geda user mailing list <geda-user@xxxxxxxxxxxxxx>
Subject: gEDA-user: photo-imagable supplies   (was: dremel "drill press")

DJ Delorie wrote:

> They seem to go where I want them. 

[jg]Great.  I'll be trying some PCB carbide bits soon.

  The deviation of the bit itself is
> far less than the alignment accuracy of the two halves of the board.
> Off by 10 mil or so - this is my first try at double sided, I need to
> try a few techniques and see which is most accurate.
> 
> I'm thinking of switching from toner transfer to photomask.  Then, I
> can drill the board first and use the holes to line up the print.

I've thought about that some, and also got a chance to do some film tests recently
that were not acceptable -- it seems no easy photography supplier films are high enough contrast
to get a good film for exposing photomask -- just dark grey instead of opaque black.  Or black and grey
if you expose it differently...

So the supplies for making a pos from a neg or a reduction in size from a 2:1 print are hard to get.
Agfa quit serving the US it seems -- I found one source that supplies super fine line
chip/interconnect making film and didn't even bother to go
through the hoops to get the price
since they were dodging around the question so much.

So, if you use toner on clear film and maybe stack two of them to get opacity, what's
your source of photoimagable mask emulsions?  I'd want some that are good with a red light
instead of any total darkness processes.   If you do photoimagable etch resist, you're all ready
to go for soldermask also... and for masks to put on conductive inks too maybe...

Conductive inks are now used in some lowest-cost-planet-wide circuit boards made in China
so they have only one side etched, and the jumper layer is mostly ink on the same side, reducing
holes to the minimum.  You sometimes have to make conductive ink wide or use a copper wire jumper
on the other side to get your desired conductance for a path,
but leaving out drilling holes is best by me...


John Griessen





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