Steel Sandwich: A PCB toner transfer experiment (Part I, the idea)
While lying in bed last night, I was going over in my head everything I could recall having learned about getting a PCB layout out of my computer and onto a piece of copper clad.
At this point in history I’ve managed to successfully iron a toner pattern onto a board only about three times, and each success came at the cost of around ten failures. The glossy photo paper is the only thing I’ve gotten to work; with magazine paper the image was too smudged to use, while with parchment paper hardly any of it stuck (though what did stick was high-fidelity). What has really been frustrating in this whole process is that there are too many variables and not enough correlation. I don’t know whether I haven’t been using enough pressure, waiting enough time, executing the correct motions, or using the right setting on the iron. For all I know, I could just have a crappy iron!
And everyone seems to have something different to try, with the most consistent results apparently from either (a) using a modified laminator for the toner transfer or (b) equipping for photoresist boards. Of the two, I would surely choose the photoresist, in part because it produces truly sharp results but mostly because the failure/success ratio seems to be lower. But both options involve buying new equipment (and in one case ruining it) with no guarantee of out-of-box success, and given the laser printer and copper-clads already in my possession, I’m already well in.
Anyway, I suddenly had an idea that, if it works, combines the even heat and pressure of a laminator with extremely low (new) equipment cost and increased controllability, the latter of which translates into more meaningful experiments and, when an experiment succeeds, more repeatable results.
What I decided was necessary is as simple as this:
- The patterns are printed in reverse on the medium of choice—for me, it will be parchment paper since it already exists in my house.
- The board is placed in alignment with the patterns on one or both sides.
- The board and patterns are placed between two flat plates of rigid metal, such as steel.
- The plates are bolted together and tightened at least to the point that nothing slides around.
- Here, the sustained flatness of the plates is important so that the pressure remains fairly even across the entire pattern.
- If you have any way to gauge it, take note of the tightness or pressure of the plates on the board. This is possibly one of the variables.
- The oven is set to the target transfer temperature.
- To be truly scientific about it, use an oven thermometer to ensure the knob is telling the truth.
- The temperature is certainly one of the variables.
- The oven is allowed to preheat until up to temperature.
- My hypothesis is that a consistent result is probably easier to obtain from a preheated oven due to variances in rise time.
- The plate apparatus is placed in the oven near the heat source.
- If the apparatus can be hung sideways from the rack, do so allowing equal heat exposure to the two sides.
- If the oven has a convection mode, it might be worth using.
- A prescribed amount of time passes.
- Another variable.
- The apparatus is removed from the oven.
- The apparatus is allowed (as by air) or forced (as by water) to cool to a safe temperature for handling.
- Maybe another variable.
- The apparatus is disassembled and the results are examined.
- An effective transfer should stick well enough that it does not lift or flake when the medium is pulled away. Therefore, the medium can be pulled away without being exceedingly gentle.
- If the result is unsatisfactory, a hypothesis is formed as to why that relates to one of the variables. The variable is adjusted and another attempt is made.
With this basic process in my head, I went to Chain Home Improvement Store to seek something I could use for the plates. What I found was square steel covers for electrical work boxes, in a flat variety with no punchouts. They already have holes for fasteners at two of the corners, and it was only $1 for the pair. I also got #10-24 stainless steel bolts and wingnuts which themselves totaled $4. This setup should adequately accommodate boards up to about 3 by 4 inches (for comparison, the standard Arduino footprint is 2.7 by 2.1 inches).
I now have all the equipment I think I’ll need to give this a shot, and that could happen as early as this weekend (and I’ll try to take photos). I really hope it works, not just because it would be convenient for me, but because it has the potential to lower the blood pressure of many other frustrated hobbyists.
- printed circuit board↩
I actually had a variation of this very same idea a few days ago but haven’t had the opportunity to try it yet. My idea was to take the PCB with the toner transfer paper attached, place it Cu-side down on a regular cooking griddle, and to clamp it down to the griddle under a small piece of thin aluminum sheet stock to evenly spread the pressure.
I’m really interested to see your results.
It sounds sane to me. I also considered aluminum, but I’m currently presupposing that it might be too flexible to apply even pressure when clamped. But if you’re not using clamps, it may be plausible as a solution. When and if you give it a try, I’d like to know how it does.
You might also be interested in another process I found while researching for this experiment in which a heavy iron plate is placed upon the heating element of a stove.