Home Etching: Toner Transfer and Photoresist
Making a board with chemicals: transfer, exposure, etch time, undercut, copper budget and drilling.
The process in outline
Etching makes a board by covering the copper you want to keep with a resist and dissolving the rest in an etchant. The resist is toner (laser-printer ink transferred to the copper) or a light-sensitive photoresist exposed through a film. The method needs chemicals and care (see Chemicals, Dust, Tools and Safety) and gives single- or double-sided boards without plated holes.
- 1. Print the artwork (mirrored for toner transfer, as a film for photoresist).
- 2. Clean the copper-clad board (scour with a fine abrasive, wash with soap and alcohol).
- 3. Apply the resist: transfer the toner, or expose a photoresist board and develop it.
- 4. Etch in ferric chloride, sodium persulfate or hydrochloric acid and peroxide, warm and agitated.
- 5. Clean and strip the resist (acetone for toner, a developer-type solution for photoresist).
- 6. Drill the holes, tin or lacquer the copper and cut to size.
Design rules for home etching
| Item | Home etching | Why |
|---|---|---|
| Track width | 0.4 mm or more (0.3 mm minimum) | Undercut and resist defects |
| Space between copper | 0.3 mm or more | Resist bridging and over-etch |
| Pad diameter | hole + 1.0 mm (1.8 mm for a 0.8 mm hole), at least 1.8 mm | Drill wander; no plating to hold the pad |
| Hole size | 0.8 mm for most parts, 1.0 mm for connectors, 0.6 mm minimum | Small carbide bits break |
| Part pitch | 2.54 mm through-hole and 1.27 mm SOIC | Finer pitch needs finer rules |
| Ground fill | Hatch or keep copper where practical | Less copper to dissolve and a plane for the circuit; but see the budget below |
| Artwork | Black as dark as possible; no gray; no fine text under 1 mm | Resist adhesion and contrast |
The design side is on PCB Design and Layout: choose single-sided routing, wide traces and through-hole parts, and add jumper wires where a trace cannot be routed.
Toner transfer
Laser-printer toner is a plastic that softens with heat and sticks to copper. Print the artwork mirrored on glossy paper (photo paper, magazine pages or special transfer paper) with a laser printer, press it on the clean copper with heat, and peel the paper away so that the toner stays on the board.
- Print on the darkest setting, without toner saving, and check that the black is solid.
- Heat and press: a clothes iron (no steam) at about 170 °C for 4 to 5 minutes with even pressure, or a modified laminator with several passes, until the paper is evenly stuck.
- Soak and peel: soak in warm water for 10 minutes and rub the paper off gently with a finger; retouch gaps with a permanent marker.
- Inspect under a lens: every track complete, no bridges.
Toner transfer is cheap and fast but is not very repeatable. Details such as the paper, printer and temperature change the result: expect to try a few times.
Photoresist
Pre-sensitized boards come coated with a positive photoresist (the exposed area dissolves in the developer). The artwork is printed on a transparency (black must be opaque to UV), placed in contact with the board under glass, and exposed to UV light; then the board is developed in a weak alkaline solution, which removes the exposed resist and leaves the resist over the tracks.
Worked example: exposure time
- A positive-resist board needs a dose of about 150 mJ/cm² of UV (typical; check the board’s sheet).
- Time = dose ÷ irradiance. A UV lamp or tube that delivers a few mW/cm² at the board:
| UV irradiance at the board | Exposure time for 150 mJ/cm² |
|---|---|
| 2 mW/cm² | 75 s |
| 3 mW/cm² | 50 s |
| 5 mW/cm² | 30 s |
| 10 mW/cm² | 15 s |
Measure the irradiance with a UV meter if you can, or do a test strip: expose a piece in steps and develop it. Too little exposure leaves resist where it should not be; too much thins the resist on the tracks.
Worked example: developer
- Positive-resist developer is a dilute solution of sodium hydroxide, about 7 g per liter (about 0.7 %): 7 g ÷ 40 g/mol = 0.18 mol/L.
- The solution is caustic: wear gloves and glasses. The resist should clear in 30 to 90 s; if it takes longer or the tracks fade, the developer is too strong or the exposure too long. A 100 mL batch needs 0.7 g.
Etching: chemistry, time and undercut
Etchants dissolve the exposed copper. Ferric chloride (FeCl3) is the classic, and stains everything; sodium persulfate is cleaner and clear but needs heat; hydrochloric acid with hydrogen peroxide is fast, cheap and regenerable, but fumes. The reaction with ferric chloride is Cu + 2 FeCl3 → CuCl2 + 2 FeCl2.
| Etchant | Etch rate (typical) | Time for 35 µm | With over-etch |
|---|---|---|---|
| Ferric chloride, 25 °C | 1.2 µm/min | 29 min | 35 min with 20 % over-etch |
| Ferric chloride, 40 °C, agitated | 2.5 µm/min | 14 min | 17 min with 20 % over-etch |
| Sodium persulfate, 50 °C | 2.0 µm/min | 18 min | 21 min with 20 % over-etch |
| Hydrochloric acid + hydrogen peroxide | 8.0 µm/min | 4 min | 5 min with 20 % over-etch |
- Warm it to 35 to 45 °C (a water bath or aquarium heater) and agitate (rock the tray, or bubble air): the reaction slows when the fresh etchant is not renewed at the surface.
- Watch it: stop as soon as all the unwanted copper is gone, as over-etching thins the tracks.
- Rinse thoroughly, then strip the resist.
Worked example: undercut and surviving track width
- Etching eats sideways about as fast as it goes down (an etch factor near 1). The 35 µm copper plus a 20 % over-etch gives an undercut of about 42 µm on each side.
- A drawn track of width w ends up w − 2 × 0.04 mm wide, and the gap between tracks grows by the same amount: a 0.30 mm gap becomes 0.38 mm.
| Drawn track width | Undercut per side | Finished width | Result |
|---|---|---|---|
| 0.20 mm | 0.04 mm | 0.12 mm | fragile or lost |
| 0.30 mm | 0.04 mm | 0.22 mm | sound |
| 0.40 mm | 0.04 mm | 0.32 mm | sound |
| 0.60 mm | 0.04 mm | 0.52 mm | sound |
For this reason 0.4 mm tracks and 0.3 mm gaps are the practical limit of home etching with 35 µm copper; thinner copper (17.5 µm, “half-ounce”) etches more finely.
The copper and the etchant budget
Worked example: how much etchant per board?
- A 100 × 100 mm board of 35 µm copper holds 350 mm³ = 3.14 g of copper (density 8.96 g/cm³), which is 49.35 mmol.
- Ferric chloride needs 2 mol per mole of copper: 98.69 mmol × 162.2 g/mol = 16.0 g of FeCl3 to dissolve all of it, i.e. 40 g of a 40 % solution.
- In theory a liter of 40 % solution (1 420 g, 568 g FeCl3) can dissolve about 111 g of copper, but it slows long before that: use about 30 g per liter in practice.
- A board from which 60 % of the copper is etched releases 1.88 g: a liter handles about 16 such boards, i.e. about 63 mL of etchant per board.
- That is why a board with a large ground fill (little copper removed) is easy on the etchant and the board that is almost all etched away costs more.
Spent etchant is a hazardous waste because it holds copper: see Chemicals, Dust, Tools and Safety for how to dispose of it.
Drilling, cutting and finishing
Worked example: drilling speed and bit life
- A 0.8 mm carbide drill at 20 000 rpm has a surface speed of π × 0.8×10−3 × 20 000 ÷ 60 = 0.84 m/s (50 m/min): fine for FR-4, but the abrasive glass wears bits quickly.
- If a bit drills about 300 holes before it dulls, a board with 400 holes uses 1.3 bits: a pack of ten bits is good for about seven such boards.
- Use a rotary tool in a drill stand or a small drill press, a sharp bit, light pressure, and drill from the copper side with a scrap board underneath.
- Cut the board with a hacksaw, a guillotine or a score-and-snap: wear a dust mask when cutting and sanding fiberglass (see Chemicals, Dust, Tools and Safety).
- Protect the copper after etching: rub it with fine steel wool and apply flux lacquer, tin it with chemical tin (a thin film), or leave the resist (toner) on and solder through it.
- Solder as usual (see Soldering); the pads have no through-hole plating, so solder each lead on the side where the part sits too if you can.
Double-sided boards
A second copper layer is possible but harder: the two artworks must register to within about 0.2 mm (use fiducial holes and a jig of two sheets with alignment pins), both sides need resist, and there are no plated holes, so each via is a wire soldered on both sides (or a hollow rivet). Most designers avoid it: lay the board out on one side with a few wire jumpers, or order a plated two-layer board (see Ordering from a Fabrication Service).
Troubleshooting
| Symptom | Likely cause | What to do |
|---|---|---|
| Toner does not stick or tracks are broken | Not enough heat or pressure; dirty copper; wrong paper | Longer heating; clean the copper; test other paper |
| Toner smears or tracks merge | Too much heat or pressure | Lower the temperature; lighter pressure |
| Copper remains between tracks | Etchant exhausted or cold; resist residue | Fresh or warmer etchant; agitate; check the developer |
| Tracks are thin or missing | Over-etched; undercut; pinholes in the resist | Shorter etch; wider tracks; retouch with a pen before etching |
| Photoresist will not develop | Under-exposed or exhausted developer | Longer exposure; fresh developer |
| Photoresist washes off everything | Over-exposed or developer too strong | Shorter exposure; dilute the developer |
| Drill bits keep breaking | Too thin, too much pressure, no stand | Use a stand, 0.8 mm or larger, light pressure |
Related
- PCB Prototyping: the overview of this guide.
- Chemicals, Dust, Tools and Safety: handling and disposal.
- CNC Isolation Milling: the alternative without chemicals.
- Choosing a Route: Breadboard to Production: when to etch and when to order.
FAQ
How long does etching take?
About 10 to 30 minutes in warm, agitated ferric chloride for 35 µm copper; a few minutes in hydrochloric acid and peroxide.
What is the smallest track I can etch at home?
About 0.3 mm with careful toner or photoresist work; 0.4 mm is comfortable. Undercut takes about 35 to 45 µm from each side.
Which etchant is best?
Ferric chloride is forgiving and slow; sodium persulfate is cleaner; hydrochloric acid with hydrogen peroxide is fast and cheap but needs ventilation and care.
Can I etch plated through-holes at home?
No: the holes are not plated. Use wires or rivets for vias, or order the board from a service.
How do I dispose of used etchant?
It is hazardous waste because of its copper and acid: take it to a hazardous-waste collection. Never pour it down the drain or onto the ground.
References
- Coombs, C. F. (ed.), Printed Circuits Handbook, McGraw-Hill (etching chemistry, undercut and etch factor).
- Etchant and photoresist-board manufacturers’ data sheets (exposure, developer, etch rates); safety data sheets for ferric chloride, sodium persulfate and sodium hydroxide.
- IPC-A-600, Acceptability of Printed Boards.
Last reviewed: October 2026. Etch rates, exposure doses and capacities are typical: follow the data sheets of your chemicals and boards.