Steam your PC Boards

By Peter Reilley <pvr@wiis.wang.com>

I have tried all sorts of ways of pc boards, except for plotting with ink on copper directly. I don't have a suitable plotter.
I have tried transparency film and release paper with only mediocre results.
The best luck that I am having now uses ordinary copier paper. I print on the paper at normal density. I am using a "super black" toner cartridge from Black Lightning. I don't think that this is necessary because I tried the output from another printer with an ordinary cartridge and got equivalent results. All of the following technique is with the super black toner.

I prepare the copper surface by sanding it with number 320 wet sanding sand paper. I do the sanding dry (don't know if this matters). I sand in small circles so the scratches go in all directions so the adhesion will not have a perfered axis.
I iron the paper onto the copper with the iron at 170 degrees C, that is the highest temperature on my iron. The fuser in my laser printers (LaserJet II and III) runs at 160 degrees C.
I iron for about 30 seconds on my counter top with a paper towel between the board and counter top. This provides insulation and a slight springiness to the board as I iron.
I iron enough to insure that every part of the paper is heavly pressed onto the board.

Immediately after ironing I place a wet (dripping) paper towel on the ironed on paper and press the iron onto the wet towel. This drives steam into the paper. Without this step the paper will shrink and pull the toner off the copper. The steam causes the paper to swell up and relieve the strain.
The iron should be placed on the towel for a split second or the paper will dry out.

I then soak the paper with dripping water and let it sit for about 5 minutes. The paper should be completely soaked and swelling between traces.
I then rub the paper with my fingers under running water. The paper will begin to ball up and come off in layers. I rub it until I get as much off as I can.
At this point the traces should be well attached to the copper and not at risk at coming off. You will find that all the toner has a paper fibers imbeded into its surface.
This is not a problem in most cases.
The problen arises when the fibers bridge the gap between traces or pads. To solve this I scrub the board with a brass brush. This brush is like a tooth brush with bristles made of fine brass wire. The brush will break the fibers that bridge gaps between toner areas. Do this while the board is wet.

Let the board dry and inspect all the toner for fibers that would prevent proper etching. Pick any remaining fibers away with an exacto knife.
While I etch the board, I periodically scrub the surface with a real tooth brush to insure that the fibers are not blocking etchant access to any portion of the exposed copper. Do not use the brass brush in the etchant as it will be desolved itself.

I have made a number of small boards up to 2 by 4.5 inches using this process and some with very fine traces and spacings.
I complete the etching of one side before I apply the toner to the other side. I don't know it this process will scale up to larger sizes well.
It seems to me that the steam step is particularly important. Before I did this traces would pull off at the edges of the board as the board cooled.
Good luck.