Making A Small Circuit Board with Press-n-Peel

James Waldby -- July 2006

Click on thumbnail or short captions if you wish to see a larger image.

Left: Circuit on paper; Right: on transfer film

Mark two sheets of paper with a "^" to show which way to place them in the paper hopper. (These marks are visible in the overall picture, below.) Print the circuit on one sheet, then place that sheet in front of the other and poke a straight pin through each circuit corner. On the second sheet, draw guide lines through the pinholes. Cut out a piece of "Press-n-Peel PCB Transfer Film" with a little room to spare; tape it to the second sheet [with one short piece of tape like "Scotch Magic", across the leading edge - see photo], and print the circuit on that sheet. Note - print a reverse image so that the transferred image will be a forward image. Note - You may need to clean the film surface with clean compressed air before printing and before transferring to board. Or do all your work in a clean-room environment.

Closer view of printing on film

Trim the printed film to the same size as the board. This makes it easier to align, which in turn makes it easier to drill. (That is, lines of holes should be parallel to board edges.) Wrap the board and film in aluminum foil to keep them aligned during heating.

Overall view of heating apparatus

I use two thrift-shop irons. One is mounted bottom-up. I cut two pieces of aluminum from 3" x 3/4" bar, each 8.5" long, and drilled 1/4" holes in the corners of one, and drilled and tapped 1/4"-20 in the other. Thin rubber sheets distribute force evenly when I bolt the two pieces together with the board-and-film package in between. This apparatus is bulky and cumbersome to handle when hot but I expect to get more-consistent results with it than when heating the board-and-film package directly between the irons. I have also made circuits using one iron rather than two, but for me two work a lot better than one.

Putting board and film on heater.

The aluminum foil wrap is to keep them aligned. I usually align one foil edge with board edge for the first wrap, ie, avoid "seam lines" over the circuit.

Board and film after heating.

In this view of the aluminum-foil-wrapped board and film after heating, a few circuit trace features are just visible in the photo. I quenched the package in a cup of water. The directions at www.techniks.com suggest cold running water but I haven't found quenching to be particularly important.

Film stripped from board.

Board, after drilling and touchup.

With a Sharpie, I filled in around the drilled holes; with a scribe, I opened lines that had filled in due to overheating. (On this first run with the two aluminum blocks, I didn't know how long or how hot would work.) I also scribed a thin line in the unused copper-pour area along the top edge, as a sort of small-feature test. Note, this board is 2.65" long by 0.70" wide, or about 67mm x 18mm, ie 12cm^2 area, with etched-away area probably less than 1cm^2.

75mL of FeCl

This 125mL Nalgene bottle contains about 75mL of FeCl, mixed up from water and a few mL of dry FeCl powder. It has been used to make 7 small boards so far, with total area around 100cm^2 and etched-away area less than 10cm^2. I have also etched some boards with hardware-store muriatic acid (HCl) mixed 1:1 with drugstore hydrogen peroxide (H2O2) in same manner as described below. The HCl-H2O2 combination works reasonably rapidly at room temperature but I don't have an easy way to store it for reuse.

Board in etchant in ziplock

Board in small (pint size?) ziplock at start of etching, at 23:05 10 July 2006.

Automatic agitation and heating

I put the ziplock bag in a small plastic tub under slowly-running hot water tap, to accelerate etching and agitate the FeCl.

Etching finished, 23:20 10 July.

Board after etching, with resist cleaned off. I used a couple mL's of acetone, and cotton swabs, to clean it, then detergent and hot water. This board will mount 3 diodes and 9 transistors in SOT-3 packages, and 12 0811-size resistors, making 9 20-mA more-or-less-constant-current LED drivers.

As assembled, top

In use, another 10 connectors will attach

As assembled, bottom

Blame the blobby soldering on absence of tinplate and solder mask