Back in the day when I was training high school electronics shop
teachers we used a variety of methods to produce PC boards. In general,
the results were very good provided the student followed the instructions.
A. Cleaning the board.
This was vital. To clean the board we'd put it under the cold
water tap for a few moments, sprinkle Comet cleanser on it and scrub
thoroughly with a Scotch cleaning pad (Scotchbright? I referred to it
as a green scrubby). Then, handling the board by the edges, rinse off
the comet and examine the board for any missed spots, fingerprints, etc.
Then place the board Cu side down on a piece of paper towel and let it
B. Getting the resist pattern onto the board.
A whole variety of methods, some better than others.
1) Use a resist pen to manually apply the resist to the board. Many
students got lots of feathery edges, breaks in the traces etc so not
good quality at all. This was mostly due to pressing too hard on the
resist pen (or using one which should have been in the garbage).
Perfectly good enough for Grade 8, though. Hopeless for boards with
IC's on them as the minimum trace width was about 0.05" or more.
2) Photo process.
a) Use a CAD program such as Auto Sketch or ACAD Lite to draw the
pattern. No auto-routing here. The student decided where to put every
trace and pad. A wonderful exercise in schematic reading. I believe we
printed the result onto tracing paper with a laser printer.
b) Get a photosensitive board.
Don't know if we just had bad stock but had endless problems
Coat a clean board with photo resist using a decoupage brush.
Hold it vertically briefly to drain off the excess
Lay it flat in a dark, dust free environment to dry (like a
cardboard box) and hope the bead of resist on the bottom edge will flow
back over the board uniformly.
The key to good results with the photo process is getting a
reasonably uniform thickness of resist everywhere on the board. This
c) Expose the board
Put the artwork on an overhead projector
Lay the board on top of the artwork
Put a big textbook on top of the board
Turn on the overhead projector for a suitable exposure time (which
d) Develop the board
Don't remember much about this step. I guess we put it in a
3) Thermal Transfer Process
This was really slick. Very easy to get really good results.
a) Print the artwork onto special Thermal Transfer paper using HP 4L
Not all laser printers of the time were suitable.
b) Place the artwork against the clean (uncoated) board with the
printed side against the copper.
c) Feed this combination into the input slot of the thermal transfer
d) Fish the board out of the water tray which it fell into when exiting
e) Carefully peel off the thermal transfer paper.
f) Admire the beautiful way in which the laser toner was transferred
from the thermal transfer paper onto the copper.
I had no trouble reliably running traces between 0.1" spaced IC
pads with this process.
4) Silk Screen
Also capable of very good results if you use a proper silk screen
exposure box. Not cheap
A definite learning curve
D. Etching the board.
1. Etchants I have used
a) Ferric Chloride
Typically sold as a liquid
If handled carelessly makes a terrible mess which is virtually
impossible to clean up.
Stains clothes irreversibly
Not allowed to pour it down the drain anymore
Lasts a long time
b) Ammonium Persulfate
I bought it in powder form
Dissolve in water to make a batch of etchant
Bleaches clothes irreversibly
Don't know current disposal requirements
Batch lasts only a few hours
Requires simple ventilation
2) Etching tank
Boards are arranged side by side on an acrylic carrier which is
submerged in the etchant. The boards are vertical and there is space
Heat is provided by consumer grade aquarium heater.
You must make sure that all parts of the board are equally exposed
to the etchant so that the rate at which the copper is dissolved is the
same everywhere on the board. There are many ways of doing this but
turbulence is simple, cheap and works well enough.
How do you get it? Use an aquarium "bubbler" pump.
Every one of the methods described is capable of very good results in
the hands of a reasonably skilled person, even the resist pen technique.
For example, for their first PC Board project my students were
required to make a PC board key tag with appropriate label in copper,
using a resist pen to hand draw the label. The idea being that they
would go through the entire process of making a PC board without it
being a big deal if it didn't look very good. I chose to label my
sample "Garage" and to this day (30 years later) my garage key is on it.
I just had a look at it and there are no feathery or undercut edges.
However, some techniques were more problematic for students than others.
In particular, the photo process worked well for some and not others
because not everybody was able to get a uniform coating of resist on the
board in the time they had available. (Several other courses competing
for their time.)
It was a happy day for the students (and me) when I discovered the
thermal transfer process.
Lest it be thought that I'm some kind of expert in this, when I started
teaching I knew how PCB's were produced in industry but how do you do it
in High School? It took a lot of trying this and that to get to the
point where my students could routinely expect that their PCB's would
turn out well (and the same for their students).
73, Jim VE7FO
On 2014-08-03 08:38, Roger (K8RI) on TT wrote:
Over the years I've tried etching boards with various methods. I have
never gotten a good looking trace. Whether the trace area is cleaned and
painted on, or photo sensitive, the edges are always irregular. They
are not straight and taper to a thin edge. Just what you don't want.
Temp, chemicals (Typically Ferric Chloride IIRC), chemical dilution,
agitation: All according to directions with the same results. I finally
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