October 1969 Electronics World
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
Electronics World, published May 1959
- December 1971. All copyrights hereby acknowledged.
Printed circuit boards (PCBs), especially
high density and many layered, were still a relatively new technology in 1969. Point-to-point
wiring was still a large part of most products in the commercial, military, industrial, and
aerospace worlds. Producing artwork and contracting for a lot of PCBs was rather expensive,
especially in small quantities. Many people, including me, made quite a few single- and two-sided
boards using photoresist pens and self-adhesive tape and pads, then bathing them in an etchant
solution of ferric chloride. Through holes were made on a drill press and then traces and
pads were tinned with flux and solder laid down on all exposed copper. Pseudo plated through
holes were made with short pieces of bare wire running through the top-to-bottom holes and
clinched down to the pads. Solder mask was not needed for small quantity runs, especially
at a time when the smallest distance between component leads (i.e., pitch) was 1/10 inch for
Here is a rundown on some of the PC kits that are readily available for
use by small laboratories or in the workshop.
The author has been associated with various satellite
programs utilizing the Agena vehicle since joining Lockheed Missiles and Space Company in
1963. Areas of responsibility have included guidance and control, communications and command,
and electrical power systems. He was previously employed by Montronics Inc., now a subsidiary
of John Fluke Mfg. Co., while attending Montana State University (BSEE). He has written for
various electronics magazines.
By Donald L. Steinbach / Senior Research Engineer Lockheed Missiles & Space Co.
Professional-quality etched-circuit boards may be produced in the small laboratory or in
the workshop. The process is neither difficult nor particularly hazardous, and special equipment
is not required. The purchase of one or more of the several inexpensive printed-circuit kits
that are available affords an excellent means of becoming acquainted with the various materials
and techniques. The kits contain all of the constituents (including instructions) necessary
to produce a limited quantity of quality boards. The kit materials may be replenished, and
the per-board cost will be reduced significantly if larger quantities of the individual items
Selecting & Using a Kit
Selecting the most appropriate kit for an intended application requires some initial familiarity
with the commonly used materials and processes. Board materials, resists, and etchants may
then be chosen to best suit the technical requirements or interests of the user.
Copper-clad PC board material is readily available in either NEMA grade XXXP phenolic paper
or grade G-10 general-purpose epoxy-glass laminates, 1/16" thick, covered uniformly on one
or both sides with copper foil, 1 or 2 ounces per square foot of board material, and with
or without a photosensitive resist coating. Grade XXXP is less expensive than G-10, is easier
to machine, and is entirely adequate for most applications. Grade G-10 should be used, however,
for high-frequency r.f. applications. The foil thickness required is a function of available
conductor width and required current-carrying capacity. A 0.100" wide conductor of 1-ounce
(0.00135") foil will safely carry 3 amperes, and the same width of 2-ounce foil (0.00270"
thick) will carry 5 amperes. Both figures are for a 20°C maximum temperature rise.
The resist is applied mechanically to an unsensitized board, or created photographically
on a sensitized board. Mechanical resists are available in tape (stick-on), dry transfer (rub-on),
or liquid form; the most suitable mechanical resists have an asphalt or vinyl base. The more
expensive photographic process requires the preparation of a mechanical or photographic negative
of the PC board layout. It is ideal when several identical boards are required, when the artwork
is to be prepared on a larger format than that of the finished board, or when the ultimate
in finished appearance is required. Both the dry-transfer resists and the photo-resists have
a limited storage life (approximately one year).
Typical example of printed-circuit kit showing all the components. The
kit shown, the Techniques No. 5003, at around $10, has ample supplies for several projects.
Ferric chloride or ammonium persulfate are the two most commonly used etchants. A typical
ferric-chloride etchant is 34% (by weight) FeCl3 in water, although the concentration
may range from approximately 28% to 42%. The mixed solution will contain a small amount of
hydrochloric acid; proprietary etchants may be modified to contain up to 5% HCl. Ferric-chloride
etchant has an indefinite shelf life, may be reused, and has a useful capacity of around 12
to 15 ounces of copper per gallon of solution. The etching time decreases with increasing
temperature; the solution may be used from room temperature up to about 160°F. Ferric
chloride attacks solder, steel, cast iron, and many other metals.
Typical ammonium-persulfate etchants contain about two pounds of ammonium persulfate per
gallon of water. A mercuric-chloride (1 ml of 27 g/l solution per gallon) or sulphuric acid
(60 ml of 96% H2SO4 per gallon) catalyst is usually added. The mercuric
chloride is poisonous, but the etchant should not be stored in a tightly stoppered bottle
because of gas release. The ammonium-persulfate etchant has a useful capacity of about 7 ounces
of copper per gallon of etchant and should be used warm (115°F typical).
When the concentration of copper reaches 5 ounces per gallon, the etch temperature should
be kept above 130°F. It is unstable above 150°F and should be used within a few days
after mixing. Spontaneous decomposition may occur if it comes in contact with ferric chloride.
Its chief advantage lies in its compatibility with most of the plated-metal resists.
All traces of the etchant must be removed from the finished board. Ferric chloride, especially,
has a tendency to contaminate the laminate substrate with insoluble forms of ferric oxide.
The etchant can normally be removed from the board by thorough rinsing and scrubbing immediately
after etching. Tape resists are simply peeled off; liquid resists, dry-transfer resists, and
photoresists can be removed by scrubbing the board with an abrasive household cleanser or
washing with a suitable solvent.
Typical Available Kits
Printed-circuit kits are available from several sources and range in price from $3.49 to
$42.95. Seven kits, representing five major vendors and priced under $10.00, were examined
and tried by the author. They represent a comprehensive selection of board materials, foil
configurations, resists and etchants. In addition to the seven PC board kits, two special
kits designed for the production of photographic artwork and contact negatives are included
in the brief summary that follows.
Editor's Note: There are many other PC kits available for use for short runs or in the
workshop. However, we are including the following as representative examples of those kits
that are most readily available from the larger electronics parts dealers.
Amidon Associates (12033 Otsego Street, North Hollywood, Calif. 91607).
E-Z Etch Printed-Circuit Kit No. 246-D ($5.95) contains dry-transfer resist. 48 square
inches (2 pieces) of 1/16" epoxy fiber glass board clad on one side with 2-ounce copper foil,
and dry ammonium-persulfate etchant crystals.
A single-board kit is available at a corresponding reduction in price. The small pads and
narrow conductor strips included in this kit will be of particular interest to IC users.
The dry-transfer resists are applied easily and rapidly. The ones shown
being used here are from Amidon Association.
The complete line of Amidon products may be obtained from Amidon, or from World Radio Laboratories.
Many of the local Lafayette Radio Electronics stores stock the printed-circuit kits.
Injectorall Electronics Corp. (4 North Rd., Great Neck, N. Y. 11024).
Printed-Circuit Kit No. 500 ($5.95) consists of 2 3" x 4 1/2" 1/16" XXXP phenolic boards
clad on one side, a resist-ink pen, resist-ink solvent, a 6-oz bottle of ferric-chloride etchant,
a 1/16" drill bit, and a 5" x 7" x 2" plastic case in which the boards are etched and the
kit is packaged. Kit is available from Lafayette Radio Electronics and other parts dealers.
Kepro Circuit Systems, Inc. (3630 Scarlet Oak Blvd., St. Louis, Missouri 63122).
Standard Kit No. S-101A ($3.95) contains both liquid and tape resists, 54 square inches
(3 pieces) of plain and perforated 1/16" XXXP phenolic board clad on one side with 1-ounce
copper foil. and liquid ferric-chloride etchant.
Professional Kit No. P-101A ($5.85) utilizes the photographic process. It contains 45 square
inches (3 pieces) of 1/16" XXXP phenolic board clad on one side with 1-ounce presensitized
copper foil mechanical negative material, photoresist developer, and liquid ferric-chloride
Both kits are available with G-10 glass epoxy boards instead of phenolic boards at a corresponding
increase in price.
Photo Layout Kit No. PL-2A ($3.95) is designed for making photographic artwork layouts
for contact or photographically reduced negatives. It contains mechanical negative material,
clear acetate film, and pressure-sensitive tapes, pads, and letters.
Photo-Reversing Kit No. FK-701 ($7.20) is a unique kit for producing high-contrast line
negatives from inked or taped artwork. The artwork is contact-exposed on the film provided
(480 square inches total) and developed with the developer supplied.
Kepro products may be obtained from Allied Electronics, Newark Electronics Corporation,
Techniques, Inc. (235 Jackson Street, Englewood, New Jersey 07631).
Experimenters Printed Circuit Kit No. 5002 ($4.75) contains tape resist, 72 square inches
(6 pieces) of 1/16" XXXP phenolic board clad on one and both sides with 1-ounce copper foil,
and the liquid ferric-chloride etchant.
Technicians Printed Circuit Kit No. 5008 ($9.75) is an enlarged version of the 5002 kit,
containing both tape and liquid resists, 128 square inches (10 pieces) of board material,
and proportionately larger amounts of the other supplies.
Techniques products may be obtained from Lafayette Radio Electronics. Do not order small
quantities of material directly from Techniques in Englewood.
Vector Electronic Company, Inc. (12460 Gladstone Ave., Sylmar, Calif. 91342).
Etched Circuit Kit No. 27XA ($6.50) contains dry-transfer resist, approximately 80 square
inches (4 pieces) of plain and prepunched XXXP phenolic board clad on one side with 2-ounce
copper foil, and dry ammonium-persulfate etchant crystals.
Vector products may be obtained from Allied Electronics, Newark Electronics Corporation,
or Lafayette Radio Electronics.
The prospective PC board user would do well to obtain catalogues from the listed vendors
and examine the other products they have to offer.
Posted October 16, 2017