Arduino Teaches Old Coder New Tricks

The cheapest and simplest method is simply to use ordinary copier paper. Once heated under pressure, the toner ends up adhering to both the paper and the copper-laminated board. The paper/copper-laminated board is then soaked under water, and the waterlogged paper is rubbed off with your fingers. This method leaves a lot of paper residue embedded in the toner's surface, this is undesirable for reasons explained later.

Many other paper types are used by various DIYers. One of the most popular is to use a high-quality magazine page that has a smooth, glossy appearance. The gloss is caused by a white clay (kaolin) coating. Because the kaolin fills in many of the pores of the paper, the toner is less firmly bonded to the paper. Second, the kaolin dissolves in water, thus freeing the toner more readily than plain paper. This method is superior to using plain paper, but it still leaves too much paper residue embedded in the toner's surface.

Another popular method is to print onto the glossy side of photo paper or backing paper for labels. This method is superior to either plain paper or high-quality magazine paper, because there is no paper residue embedded in the toner's surface. However, a significant problem with this method is actually getting the toner to stick to the paper evenly. Quite often, PCB traces simply fall off the slick surface while the paper works its way through the printer. Obviously, there is a lot of variability among laser printers and glossy paper types. I don't like variability; I like dependable repeatability.

This leads me to the paper and method I use that has dependable, predictable results. The paper is colloquially known as dextrin-coated paper. Some DIYers actually make their own by making dextrin and coat paper with it. Dextrin is simply cooked corn starch, and the process is easy albeit a bit labor- and time-intensive. Also, getting an even coat is a challenge. If you are interested, numerous articles and videos exist on the subject—simply google "make dextrin paper". I, however, feel that purchasing commercial dextrin paper is worth the cost. My preferred product is made by PulsarProFX (http://www.pcbfx.com). The company primarily sells a kit called Fab-In-A-Box, but the entire kit isn't really necessary. Instead, buy the refill package of Transfer Paper. Also buy the Green Toner Foil. Digi-Key sells refill kits of both. Pulsar really pushes use of a laminator but cautions that its laminator isn't hot enough to melt the toner used in Brother laser printers. My printer is a Brother HL-2140, so I simply use a clothes iron. A word of caution here: use genuine Brother toner. After-market toner cartridges may contain fuser oil that prevents the toner from adhering to copper. After several failed boards, I figured out that the problem was my new Rosewill-brand toner cartridge. When I put in a genuine Brother cartridge, my boards were successful again.

You need the Green Toner Foil because the toner adhering to the copper-laminated board is porous, and even though you cannot see it with the naked eye, there are sufficient holes for the etchant to penetrate the toner traces and remove metal that you do not want removed. The Green Toner Foil is ironed onto the copper-laminated board resident toner, creating a smooth, impervious surface on the top of the toner traces, resulting in superior board etches. Now, remember that I said that the aforementioned transfer methods were deficient due to paper residue embedded in the toner's surface? This is because the paper residue prevents the Green Toner Foil from making a good bond to the toner.

How do I make my own single-sided PCBs? It's fairly simple:

• Print a reverse image positive of the PCB pattern onto the shiny side of Pulsar dextrin transfer paper.

• Place the transfer paper's toner side against a copper-laminate board that has been cleaned with steel wool.

• Place a sheet of ordinary paper above the transfer paper to help prevent slippage.

• For two minutes, apply, with a few of pounds of pressure, a common clothes iron set to the highest "cotton" setting.

• Immerse into water, the ironed-together paper/copper-laminate board. After a couple minutes, the paper probably will float off. If it doesn't, lift it off.

• Dry the board, and with the toner side up, lay the dull side of the Green Toner Foil against the toner and another piece of ordinary paper above that.

• Using the same clothes iron set slightly cooler (to "wool"), iron for one minute with a few pounds of pressure.

• Peel off the Green Toner Foil.

• Etch the board as described below.

I make only single-sided boards. If you'd like to make a double-sided board, watch the video at http://youtu.be/XX7IekbCNIY. This DIYer uses HP's glossy brochure paper and seems to get pretty good results.

Etching the PCB

Having read much of what is readily available on the Web concerning DIY PCB etching, when the need arose, I decided to etch a single-sided board two different ways: first with the vinegar and salt method and second with the sponge and ferric chloride method. Some DIYers are using muriatic acid, but I have not tried that.

The vinegar and salt method works, albeit slowly. Etching my small board took two hours. The formula I used was equal parts vinegar and hydrogen peroxide and a few tablespoons of table salt. Keep adding salt until the "fizzing" continues all by itself. The liquid starts out clear but then turns an attractive shade of blue (Figure 10).

Figure 10. Vinegar and Salt Etchant