Reliable PCBs at home

From: Richard Erlacher <edick_at_idcomm.com>
Date: Mon Oct 25 09:30:21 1999

This appears to be the procedure, though I forgot to mention that the copper
has to be applied electrically to the drilled boards prior to application of
the second (after the .000030" flash of copper which is chemically applied,
but the dry-film I meant was indeed the solder mask. All my boards were
made with dry-film solder mask, since that worked so well for my wirewrap
boards. I liked the appearance, and silkscreened legends went on top of it
wit little smearing and blurring, so they could be REALLY small.

I never considered letting a shop do parts of the job, but I'll explore that
before I give up completely.

thanks for the explanation.

Dick

-----Original Message-----
From: Marvin <marvin_at_rain.org>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Sunday, October 24, 1999 10:48 PM
Subject: Reliable PCBs at home


>
>
>Richard Erlacher wrote:
>>
>> First of all, I haven't read ALL of this thread, but I recall Tony or
>> someone else replying to him saying something about the method for making
>> plated through two-sided boards in your home. I've never met anyone
aside
>> from professionals with scads of equipment who could do that, but it
seems
>> to me that the method which was described to me was to start with bare
>> fiberglass/epoxy panels, drill them, then apply a slightly conductive
>> coating in liquid form which had to be forcibly dried (perhaps baked)
before
>> the resist was applied. The boards were then exposed, the films applied
to
>> registration targets on each side, to a powerful UV light, for which some
>> prefer to use direct sunlight, and the boards subsequently developed,
then
>> etched.
>>
>> Has any of you ever encountered an approach to this that could be managed
in
>> the home environment with equipment costing, nominally, less that a
k-buck
>> or two and achieving nominally 10-mil traces with 8-10 mil separation or
>> anything close to that? How about a dry-film solder mask?
>
>First of all, there are service shops that will take a drilled board, do
the
>PTH process, and electroplate the desired amount of copper onto the board.
>The normal process for making PTH boards is as follows.
>
>The copper clad laminate is cut to panel size and drilled. The drilling is
>usually done on an NC machine. The NC program can either be supplied as a
>drill file, or it can be hand programmed. Hand programming involves taping
>the artwork (or more likely a copy) to a programing table, marking the rout
>to follow for each drill size, and then just the grunt work of centering
>each hole in a scope, and pushing a foot pedal that records that location.
>
>There are a number of different processes for doing PTH, but the most
common
>is to take the drilled panel(s), run it through an electroless copper line
>(cleaning, catalist, accellerator, electroless copper) that will put about
>30 millionths of copper on the board, and electroplate about .3 mill or so
>of copper on the bare panel (enough so the rest of the process doesn't
>create problems with the plated through holes.)
>
>The next step is imaging and how that is done depends on the required
>quantity and line density. What I used (prototype/short run shop) was use
>dry film. The board is cleaned and laminated with a photosensitive film.
The
>artwork was transferred to diazo film, and the diazo films were used to
>actually image the board. At this point, the board is developed and the
>copper you see is what you want.
>
>The rest of the process is fairly short. Electroplate copper up to the
>desired thickness, electroplate tin-lead, strip the dry film, etch, gold
>plate the fingers if necessary, fuse the tin-lead into solder, route,
clean,
>and ship. The etching is usually done by machine using an alkaline etching
>solution.
>
>Doing the process at home can be done with a minimum of equipment if
service
>shops are used for parts of the process. A small copper plating tank,
>tin-lead tank, and peroxide-sulfuric etchant along with fusing oil and flux
>can be set up at home for probably a couple hundred dollars. To set up a
>fairly complete shop including drilling and imaging would probably cost
>between 2K and 3K. This would provide the capabilities of producing
>reasonably high quality boards. Oh, did I forget to mention getting the
>experience to know how to do it :)?
>
>BTW, I think you just meant dry film above. Dry Film Solder mask does
>require UV curing and is probably impractical for home use. However silk
>screening the soldermask and legend is easy and inexpensive to do at home.
Received on Mon Oct 25 1999 - 09:30:21 BST