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Re: gEDA-user: footprints -- novice`s problems

Dave McGuire wrote:
Igor2 wrote: 
Someone sells special film for this purpose, and that costs much. I am
not an expert, so I may be wrong on the mechanism, but I think the idea
is that the laser printer doesn't use ink but some sort of polimer that is
melted on the media. If the media is paper, some of the polimer paint
works off in the paper. If you try your good old non-ball-point pen with
normal paper, it 'drinks' the ink. However, if you use the special film,
it has a shiny surface which won't 'drink' the ink or paint. The trick is
not to buy that special film, but use some shiny paper with similar
surface. This kind of paper is used for magazines and printed spam. It's
usually thicker than normal paper. (I can't translate the name of the
paper, my dictionary lacks this word.)

I could buy some in a local decoration shop, in my experience most
printers can handle ones between 100 and 130 gram/m^2. The critical part
is when the printer tries to feed the paper and it slips.

Someone reported that he was too lazy to buy such paper and used some spam
or magazine. I haven't tested this, it may be an urban legend. 

I hope this helps; if my description was not useful enough, I could
snail mail you a sample.


  Very interesting...Yes I think I understand what you're describing.
I've not tried anything like that; I would like to do so at some point.
 Perhaps soon.  Thanks for the info (everyone else too!)

        -Dave


Hi Dave,

Here are the 2 things I've used for the toner transfer method. One is called "Toner Transfer System". Interestingly nothing in the 4 pages of documentation in my leftover stash of it indicates who makes it. Doesn't matter because I didn't think it worked very well. Basically it is a shiny paper. The important bit is if you use regular laser printer paper you'll get these little paper fibers which will be stuck to the toner and they'll transfer to your board and its pretty easy to get tiny little shorts.

The other stuff I've used is called "Press-n-Peel Blue". It is made by Techniks Inc. Ringoes, NJ. This stuff is some sort of plastic sheet which feels like a transparency sheet. One side is coated with some blue stuff that gives sort of a matte finish. You print onto the blue stuff. When you iron it on and then peel it off, the blue stuff that had toner on it peels off to which gives an extra layer of etch resist. My notes from about a decade ago read: "Set iron on edge between wash+wear and wool. Let the board cool before peeling." They claim you can get 5 mil traces with this stuff but I'll believe that when I see it. I did get reasonably good results. My biggest complaint is that its really only good for 1 layer as it is rather difficult to align 2 layers. Also I don't have a chemical sink and hood in my garage along with convenient and environmentally friendly ways of dealing with the etchant. Also I never had a decent heater or agitator both of which seemed to be important.

What I've settled on is that for quick prototype builds I like to use this checkerboard material I have. I used to use a pattern of 90x90 mil squares on 1 100 mil pitch. Since then I've moved to 40x40 mils on a 50 mil pitch. This is on the top of the board and the bottom is solid ground. I've found that I can very quickly prototype things with 1206 and 0603 passives, sot-23 and similar sized transistors and DIP or SOIC parts. You can do a suprisingly good job of placing the parts so you don't need to add a bunch of wirewrap wire for jumpers. For ground connections, I just drill down and stick in a bit of 30 AWG wire and solder the top and bottom. FWIW I have prototyped a complete TV tuner
frontend with this method and had no problems with signals in the
several 100's of Mhz range. I find this method to be very fast with no real speed penalty for circuits which work up to close to a GHz. Obviously microstrip is a bit more work although at one point one could buy copper tape of varying widths. That worked better in the days of 62 mil dielectrics and not as well with a 10 mil dielectric.

For a lot of stuff though, I can wait the 2-3 days for a quick turn board house. I usually have plenty of stuff to fill the intervening hours with!

-Dan






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