OT: how big would it be? - PCBs at home

From: Allison J Parent <allisonp_at_world.std.com>
Date: Sun Oct 24 20:28:34 1999

<Has any of you ever encountered an approach to this that could be managed i
<the home environment with equipment costing, nominally, less that a k-buck

Being close to doing this I can speak about it some.

The key to doing plated through hole is a process called electroless copper
plating. I don't do that for one reason, it's a nasty process and the
materials are poison and its wastes are poison to the max. I farm it
out.

the films for high res stuff are gerber photoplots you can farm that work
out. laser printer plots are not adaquate for anything less than 25mil
features and even then... At work we pay 87$ to get B size plots from
Acad-13. This is not cheap and is likely the upper end as I get them
elsewhere for ~20 for A size.

the drilling, it's possible to build a threeaxis drill press that is NC
controlled with better than 0.005 accuracy with relative ease. that will
drill for you. With patience and a simple jig in a drillpress you can do
this by hand.

Sensitizing, exposure and development are trivial. the photoresist can be
very expensive though. They run from 300 to 800 USD a gallon (that a lot)
and getting a pint quanity can be hard. The easy way is to pour on the
resist (under safelight) and spin the board at 3000rpm for 20 sec. The
coat is very uniform then and quite thin. Exposure is a light box with
two UV lamps of adaquate size(20w, 2ft, shortwave). Development is generally
whatever the resist requries and takes a few minutes. htere are positive
resists and also negative, pick the right one to match your photoplots
(or pick the photoplots to match the resist)!

Etching the board is simple and can be handled by most hobbiests.

<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?

Dry film mask may be part of the resist used or a seperate operation. It's
not essential but it helps. A z280 board under devlopment using 10 mil
features, two sided with PTH is what I'm basing my experince on. Also
the company I work for does foil heaters and temperature sensors so the
have a minimal PCB operation (no drilling, single sided, no PTH).

Allison
Received on Sun Oct 24 1999 - 20:28:34 BST

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