IBM 1620

[Jon Elson]

On 08/30/2015 05:09 PM, Chuck Guzis wrote:
> On 08/30/2015 02:00 PM, Jon Elson wrote:
>
>> I hacked a fiber optic light pen onto a Calcomp plotter 
>> and made some
>>  artwork directly onto film, and then in 1996 I built a 
>> laser
>> photoplotter that cranks out 1000x1000 DPI images on 
>> red-sensitive
>> film at 0.6 inches/minute.  It can do up to 20 x 24" 
>> films, but I've
>> never gone over about one foot square.  The trick is, it 
>> has to be
>> VERY accurate to line up with existing PC boards.  I 
>> mostly use it to
>> make solder paste stencils, now, but originally made it 
>> for PC board
>> master artwork.
>
> That's pretty impressive, Jon.
>
> I do remember the headaches with registration of early 
> multi-layer PCBs.  Lots of rejects.
>
YIKES!  Multilayer!  I do have a system for registering 
2-layer boards, back when I used to make those myself.
You need a piece of Plexiglas about the same thickness as 
the PC board material.  You need a scrap of PC board 
material to use as a spacer between the front and rear 
artwork films.  You put this on a light table, and glue the 
strip of PC board material to the edge of the film, place 
the Plexiglas on the film and place the other film on top of 
the Plexiglas.  Glue the top film with rubber cement and use 
a magnifier to adjust alignment until it is as close as you 
can get it, then put a weight on the glued joint and leave 
it for a couple hours.  When the glue is dry, you can slip a 
photoresist-covered board between the two films and expose 
in a vacuum frame.  The two sides will come out well-aligned.

Jon