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Re: [TowerTalk] How do you get a good looking trace when etching?

Subject: Re: [TowerTalk] How do you get a good looking trace when etching?
From: Jim Smith <>
Date: Wed, 06 Aug 2014 00:42:52 -0700
List-post: <">>
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 dry.

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.
    Buy it
      Don't know if we just had bad stock but had endless problems
    Make it
      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 takes practice.

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 I've forgotten)

d)  Develop the board
Don't remember much about this step. I guess we put it in a developer bath.

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 laser printer.
      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 machine.

d) Fish the board out of the water tray which it fell into when exiting the machine.

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
    Works well

b)  Ammonium Persulfate
    I bought it in powder form
    Dissolve in water to make a batch of etchant
    No mess
    Bleaches clothes irreversibly
    Don't know current disposal requirements
    Batch lasts only a few hours
    Works well
    Requires simple ventilation

2)  Etching tank

a)  Configuration
Boards are arranged side by side on an acrylic carrier which is submerged in the etchant. The boards are vertical and there is space between them.

b)  Temperature
    Heat is provided by consumer grade aquarium heater.

c)  Turbulence
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
gave up.


Roger (K8RI)


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