Toner Transfer PCBs:
  1. Cleaning
  2. Ironing
  3. Defects

Best Results for Home Etching PCBs

Occasionally, I need to make a PCB at home rather than wait for a PCB manufacturer. A while back, I wrote an article about color PCBs that included some really poor quality boards that I made. Edges on the board had bare spots while some letters and traces were too thick at seemingly random locations. That circuit required manual correction with a permanent marker before etching.

I decided to apply a little bit of scientific process to determine how to consistently obtain higher-quality circuit boards using a clothes iron and toner transfer sheets. Specifically:

PCB Test CAD Design

I designed a sample board in a PCB layout design program.

PCB Etch Test design

PCB Etch Test design

The PCB test design includes:

The actual size of the board is only 2 inches by 1 inch.

PCB Etch Test design actual size

PCB Etch Test design actual size

Cutting and Sanding Boards

I learned from earlier experiments that you can cut copper clad boards using shears. For example, the hefty Midwest Tool and Cutlery MWT-1200 Straight Cut MagSnip cuts cleanly through common 0.062 inch thick copper clad boards. One benefit of using shears is that you don’t get dust all over the place.

Midwest Tool and Cutlery MWT 1200 Straight Cut MagSnip

Midwest Tool and Cutlery MWT 1200 Straight Cut MagSnip

In this case, I knew I was going to need several dozen boards for testing. To save time, I chose to use my table saw to cut apart a large PCB panel.

Regardless of how you cut your boards, you must remove any copper burrs from the edges. The burrs are unsightly, can cut you, and will shred sponges. Most significantly, anything that causes lack of flatness will interfere with the toner transfer process. Not only will the bumps on the edge prevent the transfer paper from making full contact with the copper, but the pressure and heat from the iron will be applied unevenly.

Simply rub the edges of the copper clad board on 320-400 grit paper to produce a flat surface.

What a difference it makes to sand the copper clad edge

What a difference it makes to sand the copper clad edge

Cleaning the Boards

The cutting and sanding contaminates the board with dust and fine bits of copper. The handling of the boards deposits oil from your fingers and equipment. Lastly, unless you are using freshly-opened copper clad stock, the copper may be stained or tarnished.

The first step to cleaning the board is to rinse it in clean water to remove loose surface contaminants. Follow this by washing the board in soapy water (dishwashing soap) with a cloth. A final rinse in clean water removes the soap.

Warning: This next section involves experimenting with and applying chemicals that are hazardous. There are several safe and effective cleaning products (dish soap, scouring pads, and Soft Scrub cleanser) that should be used unless you are experienced with chemicals and have the proper safety equipment and environment.

Because I was using old copper clad panels, my boards still had plenty of stains and discolorations even after washing. So, I next tried a variety of treatments.

Copper clad cleaning results

Copper clad cleaning results (click to enlarge)

① The first board is the 'control'. This has no extra treatment other than a soapy wash and clean rinse. Take particular note of the discoloration on the left side of the board, indicated by a blue arrow. This side of the full copper panel was exposed at the edge of the cardboard box, whereas the remainder of the panel was better protected by the sheets lying against it. The discoloration pattern originally appeared on the left side of all of the boards in the above picture. It is reasonable to conclude that boards still containing the pattern (such as ⑤, ⑥, ⑦, and ⑬) had less effective treatments applied.

② Mr. Clean Magic Eraser

③ Bar Keepers Friend scouring powder. Note the scratches and change in color.

④ Scotch Bright scour pads. Faster than powder, but more scratches.

⑤ Klean Strip lacquer thinner

⑥ MG Chemicals Flux Remover

⑦ Acetone. I think we can agree that lacquer thinner, flux remover, and acetone are ineffective at removing heavy stains on copper. Acetone definitely removes oily fingerprints, though.

⑧ CRC QD Electronic Cleaner

⑨ CLR Calcium Lime Rust Remover. Submerged for several hours. The manufacturer indicates the CLR will remove the finish from copper, but that’s probably desirable for our purpose.

⑩ Bon Ami. No obvious scratches. Gentler than other scouring cleansers.

⑪ Evapo Rust. Submerged for several hours.

⑫ Ferric Chloride. This was a disaster. I rubbed it on with a paper towel. Instead, I should have tried dipping the board in it.

⑬ Hydrogen Peroxide 3%

⑭ Drain cleaner (concentrated sulfuric acid 93.2%). Big mistake! The reaction is rapid and exothermic. The heat melted the fingertips of my nitrile gloves. I was unharmed because I was performing these tests over a utility sink with running water, plenty of ventilation, chemical-resistant gloves, and eye protection. Don’t get complacent with safety because you are “only using a small amount of a chemical on a small test area”.

⑮ Easy Off BAM (sulfamic acid <10%, formic acid <10%)

⑯ Vinegar (acetic acid) and salt. Surprisingly effective. Keep this in the back of your mind if you run out of your preferred treatment.

⑰ Wright’s Copper Cream (citric acid). Took some effort, but it looks nice.

⑱ Lysol Toilet Bowl Cleaner (hydrochloric acid 9.5%). I avoided other toilet bowl cleaners that included additional active ingredients, such as bleach.

⑲ Soft Scrub All Purpose

⑳ Sandpaper 400 grit. Heavily scratched and uneven cleaning. I also tried 1200 grit (not shown), which was really uneven in cleaning.

Recommendations for Cleaning Copper Clad Board

I have not tried etching a design onto each of the treated boards. So, I am basing my results on the appearance of the copper.

Next Step

At this point, we have cut and clean boards. Now, how do we transfer the design pattern?