A System to make PC boards

    There have been many articles about making PC boards and a lot of
different procedures.  In this article I want to explain a method,
from beginning to end, which I have successfully used to make double
sided PC boards without plate through holes.
    I have tried the Direct Etch method of making PC boards by laying
tape and rub-on patterns directly on the copper, and then etching in a
tray.  The result was fine but the process was tedious and a lot of
work to do for just one board.  The more traditional method uses
photographic techniques and photoresist to lay a pattern down on a
board.  But this method also requires an ultraviolet light source, a
contact frame and a chemical developer.  I wanted to eliminate as
many steps and as much equipment as possible. 
    In designing my system, I also wanted to spend much less time and
get a much more professional result.  I had an IBM PC compatible and
an HP LaserJet laser printer available, and I wanted to try the new
method of using ironed on toner as an etch resist.
    Depending on the resources you have available, you will want to
design your own system.  This is a system that works well for me and
the hope is that you can take my hints and build on them to create or
improve your own PC board making system. 
    The basic steps of any procedure to make PC boards are simple
enough to follow.  It is the details that require trail and error and
experience.  This article will concentrate on the details so you can
benefit from the experiences I had.   I didn't try to set down everything
since it would make this article too long. 
     For a general reference that doesn't omit any details, I found
the book Electronic Prototype Construction, by Stephen D. Kasten
(Howard W. Sams & Co. 1983) to be very useful.  It goes in depth into
all the facets of printed circuit board construction and also covers
wire-wrapping, cabling, and case design.  Unfortunately it doesn't
cover the iron-on transfer method.
    
Designing the layout

    To draft the layout, I purchased the program PC Boards for $100
from a company that advertises in Radio Electronics.   The price was
reasonable and they have a demo available for $10. 

    PC Boards
    2110 14th Avenue South
    Birmingham AL 35205
    (800) 473-PCBS
    Fax (205) 933-2954

    PC Boards allows one to lay out a double sided PC board and print
each side on an HP LaserJet printer.  On the screen, the bottom layer of the
board is displayed in orange while the top layer is shown in yellow.
Objects on both sides of the board (DIP pads, for example) are in
blue.  PC Boards has a 0.05 inch grid and you can draw DIP's of
various sizes and traces of 20 mil or 50 mil width.
    The program manual covers all of the features and you should read
it before starting.  The program is menu driven and you can select the
type of object to draw with a mouse.  I found it easier, however, to
use the keyboard to select the type of object to draw and to use the
mouse exclusively to select the end points of traces and the positions
of objects.
    Use D to place a DIP pattern (press Insert to change the size or
orientation) and T to draw a thin trace between two points.  Use K to
make a previously drawn thin trace thicker.  Use + or - to select
which layer is displayed and which layer is active.
    Put all objects which will need to have holes drilled on 0.10 inch
centers (at 1.20, 3.70 instead of at 1.25, 3.75) so you can use a
perfboard drilling mask described below.  There is a mouse
position readout in the lower left hand corner to help you do this. 
    The need to solder sockets from the top can also affect component
layout and trace placement. It is difficult to get a soldering iron in
between objects placed too close together to solder a trace to a socket
pin.
    With all the necessary reversals and shuffling of layouts, it is also
helpful to indicate the upper left hand corner of each side of the
layout.  I went through the whole process of etching both sides of a
board only to find that none of the pads lined up when I tried to
drill it!

Purchase the raw material

    I purchased the copper blanks from an electronics surplus store
for $.01 per square inch.  These were edges from industrial production
and some had stains and other gunk on them.  But they became clean and
shiny with just a little bit of scrubbing.  And they were a bargain
compared with $.30 per square inch for double sided presensitized
boards.

Clean the copper blank

    In order for the toner to stick to the copper and also so the etchant
can dissolve the copper, the blank copper board must be cleaned
thoroughly before you start to work with it.  Even if you buy
prepackaged copper blanks, you have to wash them before you use them. 
    Use gloves so that you don't put skin oils on the blank.  I used
Comet cleanser and steel wool for cleaning.  I held the board up
against the side of a wash tub with one hand and scrubbed with my
other hand.  You have to get all of the oxidation and dirt off the
board so it will etch evenly and quickly.
    Wash the board until water runs smoothly off the board and doesn't
bead up.  (check this out!?!?!)

PCB Transfer Material

    To transfer the image to the copper blank, I purchased
Press-n-Peel PCB transfer film from Techniks Inc. ($30 for twenty 8.5"
by 11" sheets).  A sheet of easy to follow instructions is included.

    Techniks Inc.
    45 J. Ringo Road
    PO Box 463
    Ringoes NJ 085551-0463
    (908)788-8249

    This transfer material consists of a plastic film with a blue
matte coating.  The toner adheres to the blue coating which easily
releases from the plastic film after ironing the toner on to your board. 

Print the Layout

    To print a layout from PC boards type hpprt.  Don't give your
input filename as an argument or it will be overwritten with printer
data.
    I tried using a sheet of transparency and a copier to invert the
top layer, but the result was too hazy.  Instead, I wrote a program to
invert the top layer of the layout to the bottom layer.  Then I
combined the two using the Load Block feature and printed both top and
bottom on the same piece of tranfer material.  This also minimized the
number of transfer sheets I needed.  At this time I also duplicated
the layout so it printed two layouts at the same time.
    Because of the reversal method, all tect on the top layer must be
shifted to the right 0.5 inches when you enter it.  Otherwise it may
overlap with an object when reversed and printed.
    Be sure to print a test run on a sheet of blank paper because
otherwise you are guaranteed to waste a sheet of the transfer
material.  Feed the transfer material into the single sheet feeder
with the blue matte coating side up.
    I had to attach a piece of paper to the back of the transfer
material so it would feed through the printer.  Use Glue Stick along
the leading edge of the transfer sheet and leave the trailing edge
free. 

Iron on the layout

    Align the two sheets for the top and bottom of the board and
carefully trim the edges in a paper cutter.  You can then use these
edges to align the sheets on the copper blank.  Use a ruler to insure
that the edge of the transfer sheet is a fixed distance from the edge
of the copper on both sides. 
    Don't remove the transfer sheet from either side until both sides
are ironed on.
    If the edge of the transfer sheet overlaps the edge of the copper, 
compare the edges of the two sheets to make sure they are even.
    I found it was easier to put the transfer sheet face up with the
copper on top of it to hold it down.  Then I heated it from the top,
through the copper blank, until it adhered to the the copper blank.
After it was stuck I turned it over and heated it directly.
    Another method of alignment is to drill some pilot holes in the
blank and to draw alignment cross-hairs on the layout when you are
drawing it.  Be sure to deburr the drilled holes with a file since any
copper sticking up will prevent the image from ironing on. 
    Heat up your iron to about 200 degrees.  I used a thermometer to check the
temperature.  You will have to experiment to find the right setting on
your iron.  Be sure to make a note of the best setting for the next
time you make a PC board.
    Iron the board on a piece of wood which won't draw the heat away
from the copper blank.  Note that the wood may tend to warp.
    The movement of the iron seemed to help loosen the blue coating from
the film.  Use the tip of your iron to trace over your entire layout
to insure that all the parts have received adequate temperature and
pressure.  Be especially careful with isolated pads and thin traces
since they are most likely to not transfer properly.
     If the image doesn't transfer a few small traces you can try
touching it up.  I didn't have much luck with etch resistant pens and
enamel didn't make very good edges (The etchant etched a little
underneath the edge of the enamel).  I had better results with the
black tape and rub-on decals that are used for photographic or Direct
Etch layouts.  Enamel was okay for a small areas if it was edged with
tape or rub-on decals first. 
    If larger areas didn't transfer, your best bet is to clean the
surface off and try again.

Etch

    I chose to etch both sides at once to minimize the amount of time
I would have to work with etchant and to eliminate an extra step.  I
decided to use ferric chloride because it was available and
inexpensive.  I paid $4.30 for 32 fluid ounces which is supposed to
etch 530 square inches of copper.
    A possible enhancement to my process would be to use ammonium
persulfate etchant.  This is a cleaner etchant to work with and turns
blue as it is used up so you can tell when you need to change it.  But
I couldn't find a source for it (Active Electronics advertises it but
doesn't sell it any longer).  Also, it is a weaker etchant.
    I wanted to etch the board vertically so the etched copper crud would
fall off the board.  I thought I would be able to see both sides of the
board as they etched.   Unfortunately, you can't see through ferric
chloride etchant.
    Fortunately, there are other advantages.  When a board is etched
vertically you don't have to worry about one side etching faster than
the other (since conditions on both sides of the board are similar).  Also, if your
board is too long to etch completely at one time, you can etch it one
half at a time.  I was worried that the center would get over etched,
but the board that I tried this with was flawless. 
    I ordered an Etch Tank System from Circuit Specialists because the
price was right but when they said it would take four weeks, I decided to
build one myself.  This choice was only cheaper because I had an extra
heater, bubbler and plastic material that I could use.

    Etch Tank System (ET-10) from Circuit Specialists ($44)
    P.O. Box 3047
    Scottsdale, Arizona 85271
    (602) 464-2485
    1-800-528-1417
    Fax (602) 464-5824

    Circuit Specialists sells many PCB making supplies through their
catalog, and they are a great source for chips and components for the
electronics hobbyist. 
    To make my tank, the article Make Your own Etching Tank by Tony
Lewis, p.45-50 in Radio Electronics, December 1989, was indispensible
and the task was easier than I thought.  The article also includes
useful general information about PCB etching.
    I suspended my board with fishing string by two holes I drilled in
the board.  If the etchant isn't deep enough, just add some more
water.  The etchant won't be as strong, but at least it will etch the
board. 
    I was surprised by the large effect heating and agitating had on
the etching time.  My ten inch square board only took about ten
minutes to etch.  Of course, the etching time depends heavily on the
etchant temperature, concentration (was it used before?) and amount of
agitation.
    Heat the etchant to about 100 degrees Fahrenheit.  You have to be
sure the temperature of the etching solution doesn't rise above 180
degrees Fahrenheit since the toner will melt and come off the board. 
    I removed the heater once the etchant was heated because it was
getting in my way and the etchant didn't cool down too much in a the
time it took to etch a board. 
   Don't put any metal in the Ferric Chloride.  I thought I could just
discard the corroded bolts I had used as standoffs, but they actually
protected a region of copper around them and didn't allow it to
dissolve in the etchant.
   Finally, don't mistake the trademark symbols printed on the
fiberglass board for copper that still needs to etch off.

Clean the board

    To clean the toner off the board, you can use acetone (nail polish
remover) to dissolve it.  But this uses a lot of acetone and the toner
that comes off tends to stain the fiberglass between the traces.  A
better method is to use the steel wool and cleanser again.

Drill

    A drill press of some sort is really necessary for drilling the
holes.  Holes have to be very accurately positioned and the thin drill
bits needed break very easily if you pull them out at the wrong angle.
The reference book has a good section on drilling and types of drill
bits. 
    Use a piece of perfboard as a drilling template.  Draw circles
around the holes to drill through so you can find them quickly.  Since the
perfboard already has holes at 0.1" intervals, you don't have to worry
about DIPs not fitting in once you have drilled all the holes.  Even
if the individual holes are a little off, the error won't build up and
they will all be near enough.
     Use double sided tape to stick the your board and the perfboard
together.  The idea is to keep the two pieces from sliding against each
other, so loops of regular tape won't work.
     Hold the board so that it can move sideways as the drill bit
feeds into the perfboard, but be sure to press down firmly when the
drill bit is withdrawn so it doesn't get caught.  This catching was my
most common cause of drill bit breakage.
    
Install sockets

    Since these boards don't have plate-through holes, low profile
machined sockets are necessary to allow you to solder socket pins to
traces on the top side of the board.  I also found some sockets pins
on a carrier at the local surplus store.  They need a bigger hole, but
you just solder them in and pull out the carrier.  You have to be
careful, however, not the fill the socket with solder when soldering
the top side. 

Conclusion

    The first time you try any system, it takes a long time.  The
second time goes much more smoothly as you begin to learn what to
expect.  This is an outline of my system, and some hints on things I
learned which made the process run more smoothly.
    I hope that you will find my ideas useful for making PC boards and
that this article will help you to avoid some of the pitfalls I
encountered. 

Enhancements
    Dyna Art Toner Transfer system ($9.95 + $2.50 shipping + 8.25 Cal
tax if necessary)
    Dyna Art Designs
    3535 Stillmeadow Lane
    Lancaster, CA 93536
    (805) 943-4746
    Popular Electronics August 1992, New Products, p.86
    Circuit Cellar Ink, The Computer Applications Journal,
        August/September 1992, From the Bench, Jeff Bachiochi, p.80-84

    Better software

References
    Magazine articles
    Books
    Making your own PC Boards, by Carl Laron, Radio Electronics
February 1988, pp.51-54, 70 covers other methods of PC board
fabrication that I chose not to use but might be useful for different
applications.  It is a good overview of what materials are needed for
other methods of fabrication.  (re-write all of this)

    PC-board breakthrough, Hardware Hacker, by Don Lancaster, Radio
Electronics December 1989, pp.68-76

    Developing and Etching a PC board, Drawing Board, by Robert A.
Grossblatt, Radio Electronics December 1989, pp.77-78

    Direct Toner PC update, Hardware Hacker, by Don Lancaster, Radio
Electronics February 1990, pp.69-71
