raoul@eplunix.UUCP (Nico Garcia) (05/24/90)
Thank you, folks, for the pointers on this technique. I tried it today, and after several attempts, finally got a decent board out of it. The July issue of Popular Electronics does indeed have an article on the technique. However, the author says to use TEC-200 transparencies, and gives two places to get it. Unfortunately, the only phone number he gives is for a *different* DC Electronics. The correct number is (602) 945-7736. They now have a minimum one-week back order, due to the article, and it'll get worse before it gets better. I tried to find some office supply place that had heat-fused laminating film, which the article suggests as an alternate. Unfortunately, all the office supply places I tried here (Boston) said they'd have to special order it. So I took several people's advice and tried running ordinary transparency sheets through a Macintosh Laserwriter. My artwork is in Mac files anyway, so that was no loss. This didn't work very well, with poor trace adhesion. Taking paper artwork from the Laserwriter and copying it onto the transparency with our office Xerox machine worked much better. For those of you who want to try it: Make your artwork, making sure that the traces are not closer than, say, .02 inches, and a minimum line width of .02 inches. Copy it onto the transparency. Trim your transparency to the size of your board, with one side or corner sticking beyond the board. Trim, scrub, and degrease your PC board. Make sure all your surfaces and materials are clean and dry. Scotch tape your transparency onto your board, making sure that there is an edge (that protruding one) that you can grab to pull it off. (For we who make double-sided boards, make sure your other side is lacquered before taping.) Place the board on a flat non-heat-sink: I used a notepad and paper towels. Place a clean piece of thin paper or cotton cloth on the board (I used a piece of notebook paper, so I could see through it to the traces). Place a very hot pre-heated iron (290 degrees, or the cotton/linen setting, and give it 10 minutes to heat up), on top of the paper and board for 10 seconds. Then, with moderate pressure, rub the paper and board for another 20 seconds. With the tip of the iron, go over the entire pattern to make sure it all adheres properly. Last, immediately after removing the iron, grab the protruding transparency edge and gently peel it off. Be careful: the copper is still quite hot. (Believe me: Ouch!) That immediate peeling part is the trick that Popular Electronics failed to mention. I had to strip 3 boards before I got that right. Don't forget to touch up your board with a resist pen and an sharp knife. If anyone finds a place to get better plastic, such as a New England distributor for that TEC-200 stuff or a supply of heat-fused laminating film in Boston, please contact me. -- Nico Garcia Designs by Geniuses for use by Idiots eplunix!cirl!raoul@eddie.mit.edu
pa1487@sdcc13.ucsd.edu (pa1487) (05/25/90)
Instead of immediately removing the transparency, take the whole assembly and run it under a cold tap. The hardens the toner and makes a better transfer and since the toner isn't melted anymore, its less likely to tear and stretch... I've also heard that putting the board in the freezer "fuses" the toner to the board. GBell