OT: how big would it be? - PCBs at home - test-drb@ccmp.vtda.org

22 Oct 1999

-----Original Message-----
From: Marvin &lt;marvin(a)rain.org...
  To: Discussion
re-collecting of classic computers
&lt;classiccmp(a)u.washington.edu...
  Date: Friday, October
22, 1999 4:37 PM
Subject: Re: OT: how big would it be? - PCBs at home

...

daniel wrote:
...
  > Making PCBs at home is a ridiculous waste
of time. I have a vacuum lightbox
...

That really depends on what you want to do. Before I started a printed
circuit mfg company, I did make them at home for considerably less money
that it cost to have them made. 
We tried use both silk screening and pre-sensitized boards in the beginning.

...

> here as well as a commercial processing system, a silk-screening set up, even
...
 > a wave solder machine in my home and nothing
compares to what the big guys
...
 > can do and charge for the same thing. My last 
*production* company use to
...

Again, what are you trying to do? Silk-screening circuits require a fine
stainless mesh and a good chase unless you are only after a crude, make it
work, type of PCB.

I know. We had a unit made up by a screen manufacturing place. I still have
a few steel frames with stainless mesh. It worked pretty good on small runs
but I really like to have boards solder masked and plate through holes.

...
 > make its own prototype doublesided PCBs in house
and it wasn't worth it. I
...
 > have a company I use now that will make me a
double sided PCB, GOLD PLATED
...
 > contacts, solder mask both sides (pre-drilled of
course), and silk screened,
...
   and cut for
less than a $1 a board in quantities of 500. 
Need to mention the board size, number of holes, and setup charges for that
$1 a board to mean anything :). 

2" x 3", he never cares about the number of holes. It was always the same
price. On 3X3 we had some discretes, a few 44 pin PLCCs and an 18 pin PIC.
The guy has done thousands of boards for me (before I shipped the entire job
to Taiwan).

BTW: No set up charges.

...

> Pre-sensitized boards are useless as they usually come flawed and the
> coating thickness is not consistant. The company I use now  for PCBs used a
...
 > "roll" of sensitized film that was
"ironed" onto a 3' X 3' board. Far better
...
   process.

Using dry film is an excellent approach used by most professional PC board
houses, and the equipment isn't all that expensive (depending on your frame
of reference.) Older dry film laminators can probably still be had in the
$1k area. Of course, at a $100+ per roll of dry film, and the fact it has a
limited shelf life make the process impractical unless a number of boards
are being made on a regular basis.

Yes, he gave me a tour. He drills the boards first, then photosensitizes
them. They get UV, then he develops them in water (I think it was). Then he
electroforms copper to create plate through holes, then tins, then gold
plates, I think then he did the solder mask on both sides (I am sure that
was silk screened) and finally the boards were silk-screened (layout), then
cut. Turn around time was generally 4 days.

...
 > Don't forget a good GERBER and NC drill file
is needed and most PCB
> manufacturers find little problems with the files that you may not uncover
...

Actually there are a number of ways to make artwork; Gerber files and NC
files are not required. An NC drill file can be created from artwork. I have
...
 seen camera ready artwork produced by electrical tape
on a piece of mylar
(funny but true), produced by linotronic printers, printed by dot matrix
printers, and a number of other ways.

He always wants the NC file for his "quad" drilling CNC machines, they also
carve out the board "shape". I think he uses the Gerber file to print out
artwork for the film he needs for the various processes.

...
 FWIW, a local shop will also produce undrilled pc
boards just printed and
etched for about $0.30/sq in total cost. This is a wonderful service for
fast, inexpensive prototype SS or DS circuit boards. 

If they are not drilled then you do not get the plate through holes :-(

Drilling is no big deal for this guy... He drops 4 sets of 5-10 boards (at
least 18" X 24") on a quad head CNC and it drills them REALLY fast...

john

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