Instructions for Making Printed Circuit Boards
The process presented here is based on an article by Larry Ball in Electronics Now1. Several
students at in the Electrical and Computer Engineering program contributed to detailed
instructions below. Following the steps below will help you build working circuits, however, it
is not completely failsafe and some errors and touch ups are generally required.
Overview
Printed Circuit Boards (PCBs) start out with copper on one or both sides. The continuous layer
of copper must be divided into conductive wires separated by insulating spaces. Many of the
steps described below are dedicated to transferring the pattern of conductive wires and pads to
the PCB. The circuit pattern is drawn using standard features based on the components used and
the connections specified by the electrical schematic.
The technique presented here takes the circuit pattern printed on special toner transfer paper and
irons that pattern onto a clean copper surface. A chemical etching solution dissolves the exposed
copper and the toner protects the copper lines that become the circuit wires. After etching it is
necessary to drill holes in the board for the component leads to pass through the board. Finally,
the component leads are soldered to the copper wire lines to complete the electrical circuit.
Several common pitfalls will be discussed along with repair methods. The most important step is
to CLEAN THE COPPER SURFACE thoroughly. A clean surface improves the adhesion of the
toner to the board, which in turn increases the quality of the etched board. If conductor lines are
etched through (making an open circuit) then it is necessary to solder a jumper wire over the gap.
All of these issues will be covered in the following pages.
Pattern Preparation
For the circuits built during the workshop, we have already prepared the patterns using a free
software program called EAGLE2. You can create your own patterns from a schematic using the
software or by hand using templates. Templates are necessary to match the circuit pattern to the
leads on the components. For example, an 8 pin DIP IC package must match a set of eight holes
properly spaced out on the board and the conductor lines must connect the proper pins to the
other circuit components. Conductor lines and spaces should be as large as possible to increase
the odds for successful pattern transfer and etching. Wherever possible, conductor lines and
spaces should be 30-50 mils wide (1 mil = 0.001 inch = 0.025 mm = 25.4 µm). Smaller lines
will not transfer and etch reliably. A typical via (donut) hole size is 70 mils outer diameter and
30 mils inner diameter. It is permissible to pass conductor lines under components using the
component as a bridge over the conductor line. Lines can also pass between the leads on an IC
chip, such as a DIP, by making the conductor line narrower to prevent a short circuit connection
to the adjacent via hole donuts. Rub on lines, donuts, and standard component templates can be
purchased from electronics suppliers or catalogs. One other option is to have a prepared drawing
that can be photocopied onto the toner transfer paper.
1
Larry Ball, "Make Your Own PC Boards Using Toner-Transfer Products", Electronics Now, Vol. 68, No. 8,
August 1997, pp. 48-51.
2
www,cadsoftusa.com EAGLE can be downloaded for FREE with a limit of 3x4 inch boards.
KEEP –Kentucky Electronics Education Project
Janet K. Lumpp
jklumpp@engr.uky.edu
It is also useful to have a box drawn around the circuit pattern that corresponds to the size of the
circuit board. During the iron on step the box outline helps align the board and pattern.
Pattern Printing
The toner transfer paper is somewhat like a decal. The features on the paper are transferred to
the circuit board surface and the backing paper is soaked off in water. Print onto the shiny side
of the Press and Peel Wet paper. It is necessary to make a VERY DARK print on the toner
transfer paper with a large amount of toner. The toner will protect the copper during chemical
etching so more toner ensures better etching resolution. Refer to the instructions on the toner
transfer package. In general, a dark print can be accomplished by increasing the print density on
a laser printer or by increasing the darkness on a photocopier. If the open white areas become
gray, that is OK. The chemical etchant will etch through this thin layer of toner.
Placing several patterns on a page will help conserve the toner transfer paper. After printing the
individual patterns can be cut apart in preparation for ironing onto the board.
Board Cleaning
A CLEAN COPPER SURFACE IS CRITICAL. Copper forms an oxide coating when exposed
to air and humidity exactly like the darkening of pennies and green coloring of a copper roof or
the Stature of Liberty. The toner will not adhere to the copper oxide and it is therefore critical to
remove this layer before ironing on the toner transfer printout. Scotchbrite scouring pads are
used to scrub the oxide layer off of the copper. Press firmly and scrub for at least one minute.
Scrub in a circular motion in the center of the board and parallel to the edges of the board. Fine
black dust should come off during the scrubbing process. Scratches on the copper from the
scrubbing process are OK. The copper should look bright and pink in color.
After scrubbing thoroughly, rinse the board with water and dry with a paper towel. Hold the
clean board by the edges to prevent any fingerprints on the surface. Fingerprints contain oil that
will prevent the toner from sticking to the surface. If the surface does become soiled, scrub
again, rinse and dry. Iron on the pattern immediately after cleaning.
Iron On Pattern Transfer
The toner transfer pattern is bonded to the copper by heat and pressure using a clothing iron.
Preheat the iron in the no-steam mode and set at the beginning of the steam range. Place the
clean copper board on a heat safe surface such as a wooden board with the copper facing up.
Place the toner transfer paper face down on the board aligning the edges of the board with the
box outline on the pattern. Press down firmly with the iron and hold in place for 60 seconds.
Move the iron every 60 seconds for a total of five minutes to ensure even heating. DO NOT
allow the iron to slide as it will smear the toner and blur the pattern. Heat, pressure, and time are
necessary to melt the individual toner particles into a continuous black coating on the copper
surface.
After ironing, place the board in a dish of water with the toner transfer paper facing up. Allow
the board to soak until the paper floats up off the circuit board, approximately five minutes. The
KEEP –Kentucky Electronics Education Project
Janet K. Lumpp
jklumpp@engr.uky.edu
result should be a clean piece of paper and a complete black pattern bonded to the copper
surface. If some pieces of toner are not well bonded to the copper, they can be repaired prior to
etching.
Pattern Touch Up
If there are major errors in the pattern - missing lines, blurring, and misalignment of the pattern
and board - then it may be necessary to scrub the board clean and iron on an new pattern. Small
errors can be repaired by drawing the missing sections with a permanent Sharpie marker. Rub
on lines and donuts can also be used to repair patterns.
At this point it is also useful to write initials or some other marking on an open area of the
pattern to identify whose board is whose. Using the permanent marker, make dark letters by
going over the letters at least twice. Dark letters will etch better just like the dark toner will
protect the conductor lines.
Etching
Several hobby class etchants are available in electronics shops and catalogs. The ferric chloride
solution or anhydrous solid that you can dissolve in water will etch copper quickly but is more
expensive. The less expensive alternative is sodium persulfate sold as a white crystalline powder
you dissolve in water. Etchant solutions are CORROSIVE and should be treated as hazardous
materials. WEAR GOGGLES AND GLOVES when working with the etchant powders and
solutions. Mix the solution according to the directions on the container. For sodium persulfate
the ratio is 1/2 pound per gallon. Tap water is fine or distilled water. Fresh solution will etch
more quickly and a solution that has been sitting for several weeks may not etch well. Heat
accelerates the etching process and sodium persulfate solution etches effectively at temperatures
up to 70°C. Using a Pyrex glass container, the etchant can be heated with a hotplate or Bunsen
burner with a thermometer for temperature monitoring. Professional etching tanks with heaters
and agitators are also available for approximately $120 and hold 1.5 gallons of solution.
Depending on the temperature of the etchant and the area of the circuit board, etching time varies
from 20-60 minutes. Circuit boards should be placed in the etching tank using tweezers or tongs
so that the copper is exposed to the etchant without other boards overlapping. Stir the etchant
occasionally to bring fresh solution in contact with the copper.
Initially it is difficult to observe any progress in the etching process. The copper color changes
slightly and the scratches disappear. Eventually the copper becomes thin enough to allow the
underlying board material to show through and the edges of the board come clean first. The
solution turns blue-green as the copper metal is converted to copper sulfate in solution. The
etching process is complete when the visible copper is gone and the only remaining features are
the black pattern lines. Under these lines are the copper conductor wires that will connect the
electrical components. Etched boards should be rinsed in clean water and dried with a paper
towel.
Via Hole Drilling
A hole must be drilled for each component lead. Small hand drills work best because they are
easy to control. With practice, a power drill such as a Dremel tool can be used to drill holes
KEEP –Kentucky Electronics Education Project
Janet K. Lumpp
jklumpp@engr.uky.edu
faster. WEAR GOGGLES while drilling because the fine drill bits snap easily. Place the circuit
board on a piece of scrap wood to protect your table surface. Hold the drill perpendicular to the
board and try to drill straight through not at an angle. Refer to the layout pattern to make sure all
holes are drilled. You may also need some larger holes for mounting a battery clip. A careful
job of drilling will make it easier to insert components and prevent the awkward job of drilling
holes in a partially assembled board.
Toner Removal
The remaining toner may be scrubbed off with the Scotchbrite pad or washed off with acetone to
reveal the underlying copper. The copper must be exposed to allow the solder to make contact.
Toner removal should be done just before soldering so that the copper does not oxidize.
Component Insertion
Components are inserted from the blank side of the board with the leads sticking out through the
copper donuts on the backside. The leads on axial lead components must be bent into a U shape
and three-lead components need to be separated into a tripod shape. The orientation of
components is CRITICAL to the operation of the circuit. All components have a specific
orientation in a circuit with the exception of resistors and some capacitors. The schematic,
layout, and component placement drawings will help you determine the correct orientation for
each component. For example, transistors are usually drawn as a half circle with the flat side
facing one direction and LEDs are drawn with one black side indicating the shorter lead.
Integrated circuit chips are easy to misalign by 180 degrees. The top of the chip is marked with a
half circle notch or a white stripe, or pin number 1 is marked with a circle. For example, if
power is supposed to go to pin 1 and the chip is in backwards, the power might be going to pin 5
or 8. The circuit will certainly not work as designed and the chips may be damaged if powered
up incorrectly. Attention to detail will save debugging time.
After insertion, the leads may be bent slightly to keep the component from falling back out of the
holes. Bending the leads is called clinching. Do not trim the length of the leads until after
soldering. In general, you can insert a few components at a time, clinch the leads, solder, trim
the leads and then insert a few more components. The short pieces of wire trimmed from
components are useful for repairing open circuits where the copper has been etched through.
Keep a few pieces until you are done debugging and repairing a circuit.
Soldering
Please refer to the handout on solder safety, proper technique and desoldering methods.
KEEP –Kentucky Electronics Education Project
Janet K. Lumpp
jklumpp@engr.uky.edu
Circuit Board Processing Steps
1. Prepare the pattern on the iron on transfer paper.
2. Trim the pattern to the size of the board.**
CLEAN IMMEDIATELY BEFORE IRONING.
3. Clean the copper surface thoroughly with a Scotchbrite pad.
4. Wash the board in water and dry.
5. Preheat the iron to the beginning of the steam setting without steam.
6. Prepare a tray of water.
7. Place the circuit board on the wooden board with copper facing up.
8. Place the pattern face down on the copper.
9. Press firmly with the hot iron for 5 minutes moving every 1 minute. DO NOT slide the iron.
10. Place the circuit board in the tray of water with the paper facing up.
11. Wait for the paper to float off the board.
12. Dry the board.
13. Inspect the pattern and repair any missing lines with the permanent marker.
14. Label the circuit board with your initials if you are processing multiple boards.
WEAR GOGGLES AND GLOVES WHEN WORKING WITH ETCHANT.
15. Mix the etchant powder in water at the proper ratio.
16. Preheat the etchant solution to 40-70°C.
17. Place the patterned circuit boards into the etchant bath.
18. Stir occasionally and monitor the temperature.
19. Remove the etched boards, rinse with clean water, and dry.
WEAR GOGGLES WHILE DRILLING.
20. Drill holes.
21. Scrub off remaining toner with Scotchbrite pad or rinse with acetone.
22. Preheat soldering iron.
23. Wet soldering iron sponge.
24. Insert components, clinch, solder, and trim leads.
25. Test circuit.
26. Troubleshoot and repair as needed.
**If you will be etching the same day as ironing on the pattern, you may mix and preheat the
etchant at this point (Steps 15 and 16).
KEEP –Kentucky Electronics Education Project
Janet K. Lumpp
jklumpp@engr.uky.edu
Supplies
Other supplies that are not included in the Electronics Assembly Kit.
Etchant
Etching dish
Heat source
Thermometer
Tweezers or tongs for removing boards from etchant.
Circuit Supplies
Press and Peel Wet transfer paper
Circuit schematics and layout patterns
1 ounce copper printed circuit boards cut to size
Components
The vendors listed below sell supplies that are consumed during circuit assembly. Additional
suppliers are listed in the Kit List for the Electronics Assembly Kits.
Vendor
Injectorall Electronics Corporation
110 Keyland Court
Bohemia, NY 11716
800-878-7227
FAX 516-563-3389
www.injectorall.com
Techniks Inc.
PO Box 463
Ringoes, NJ 08551
908-788-8249
www.techniks.com
Electronix Express
365 Blair Road
Avenel, NJ 07001
800-972-2225
www.elexp.com
Chaney Electronics
PO Box 4116
Scottsdale, AZ 85261
480-451-9407
Micro Tools
PO Box 6505
Vacaville, CA 95696-6505
707-446-1120
www.micro-tools.com
Products
Sodium persulfate: 1/2 pound and 10
pound bottles of salt powder.
Press and Peel Wet transfer paper: packs
of 5, 10, 20 or 100 sheets.
1 ounce copper printed circuit boards.
Soldering irons and stands.
Solder and desolder wick.
Hand tools.
Ready to solder project kits.
Fine gauge drill bits.
KEEP –Kentucky Electronics Education Project
Janet K. Lumpp
jklumpp@engr.uky.edu