Printing on aluminum?

[nheng]

I've had good luck with the blue PNP sheets but the copper definitely has to have "teeth".

Scrub the copper (or other metal if you're labeling with it) with an old toothbrush and Comet or other abrasive cleanser. Rinse with clean water, wipe the water off with a paper towel and never touch it again ! I put about 20 sheets of old letter paper on a flat surface, under the pcb and one sheet on top of the blue sheet. Press with a hot iron (highest setting) without moving for about 10 - 20 seconds, then move to a few different orientations (probably helps to make it "hit" all areas).

Do not move the iron while applying more than light pressure as you may smear or distort the heated toner below.

Cool under running water before peeling away the sheet. The last board I did was about a month ago and had 4 or 5 tiny SSOP packages on it. Not perfect but had 98% continuity before touchup.

This would probably not work on any thicker material (1 oz. pcb is 1.4 mils thick) without a preheat or baking as mentioned.

[mr coffee]

I've spent a lot of time trying to get PnP blue to work well on both copper clad and Aluminum panels.

I highly recommend three other things I've found helpful.

1) AFTER you clean with Comet or whatever and rinse, go over the board\panel with Scotchbrite and wipe the panel off with plain white paper towel before applying the PnP. If you have a ceramic cooktop on the stove, it seems to make an idea base to do the ironing on.

2) After you peel the backing and have a successful transfer of the pattern to the panel, iron a second BLANK piece of PnP Blue onto the toner image on the panel. Then (of course) peel the second backing off and etch. This seems to make a thicker resist that allows etching 2 oz + copper clad and put deeper images in Aluminum.

3) Don't plunge aluminum into the etchant. Apply the etchant with a soft paint brush and rinse and check frequently. It will take 10 minutes instead of 10 seconds, but the detail will be a lot better. The violent etching by immersion takes some of the PnP off with it if you plunge it into etchant.

[lwalker]

Interesting.
I usually clean the copper with degreaser and rinse well since I thought that it was oils, etc that was causing poor adhesion. I'll try going over it with fine sandpaper to give it a better surface; in fact I have an LED power flasher board I'd like to test it with.

I would love to try etching aluminum: what kind of etchant do you use? I have ferric chloride, but a friend has some ammonium (?) persulfate he wants me to take off his hands also.

[Evan]

This is something with which I am familiar. Toner transfer sheet were developed a long time ago shortly after the Xerox Standard Camera was developed and sold. It predates the first real copier and is a large format studio camera that uses selenium plates and the xerographic process to develop an image.

The problem now is that in the 1980s certain patents on magnetic roll development held by Burroughs expired. Xerox immediately took advantage of this and began switching over to mag roll development systems. This requires that the toner be magnetic and so it is compounded with ferrite powder. This magnetic toner doesn't work worth squat compared to the non magnetic toner in the pcb transfer process.

This is easy to test. Print a small patch of solid black on a piece of ordinary paper and cut it out. See if it is attracted to a super magnet. If so, and there will be no doubt, then you need to find a machine that doesn't use magnetic toner. They still exist as not every manufacturer jumped on that bandwagon or for every model. It does have some disadvantages. Another thing to try is a color laser and print the image in solid magenta toner only. It can't be compounded to be magnetic unless they have made some recent discovery I haven't heard about.

To etch aluminum use a weak lye solution.

[Mad Scientist]

I started out using PnP’s paper backed product and quickly decided that it was an exercise in frustration. Then switched to their mylar product, after much experimenting I am able to get it to work reasonable well. As already mentioned the board must be spotlessly clean and have a slightly roughed up surface. I use steel wool followed by an alcohol wash.

Don’t have a laser printer so I use a copier to put the image on the film. Copier is set to its darkest position to put the maximum amount of toner onto the film. (It’s the “plastic” toner that is the acid resist material. Hence the more the better.) Try to avoid touching the printed image, don’t want oily finger prints here.

Next is the tricky part, transferring the image to your metal/pcb. The goal here is to apply enough heat and pressure to re-melt the toner so it will stick. Too much heat and pressure and the image will mush out and become fatter. Not enough heat or pressure and it will not stick. 250 degree heat is not too hard to obtain but the correct pressure is trial and error.

2) After you peel the backing and have a successful transfer of the pattern to the panel, iron a second BLANK piece of PnP Blue onto the toner image on the panel. Then (of course) peel the second backing off and etch.

I have not tried this and not sure how it would help. Perhaps the reheating will cause the toner to stick better.

I would love to try etching aluminum:

Many years ago my mother made etched aluminum trays by hand painting a design on them with asphalt paint then etching them with muriatic acid. The acid would not bother the paint put it was easily washed off with turpentine. The toner being plastic should also be able to resist the acid. But I think I would want to start of with a diluted mixture.