At 02:13 PM 3/28/01 -0600, Eisermann, Phil [Ridg/CO] wrote: > As for the other questions: I connect two layers with wires inserted >through the holes. When I am laying out a board for myself, I try very hard >to minimize the number of through holes, because aligning the layers is such >a pain. Not as much as drilling all those through holes, and then shoving >#30 wire through them. I could make the holes bigger i suppose. I (we) make a lot of proto boards here at our shop. I worked out a technique for registering the negatives when making double sided board that has worked very well over the past 20 years or so. Its so simple that I feel embarrassed to mention it, except that it works! Just take a scrap of the exact same PCB material that you are exposing (with copper surfaces). Cut it into an "L" shape, with 1 leg at least 2" long and the other leg at least 3 or 4 inches long. Take your time when cutting the inside corner: make it nice and square, with smooth edges. We make ours about 3" x 4", with 1" wide legs. Think of a carpenters square. Cut the board that you want to expose about 1/2" larger than you need. This leaves a border of about 1/4" of waste material you will have to cut off when the board has been etched. Its a PITA but you need the space. The board you are going to expose sits in the inside corner of the jig. Since this little jig is made of the same material as the board, it is the same thickness. That is important. Attach one of the transparencies to the jig. Position it so that the actual image is about 1/4" away from both arms of the jig. Tape it to both arms of the jig using thin Scotch Tape. Flip the jig over and position the other transparency on the jig. Line up the holes in the center of the pads. Tape only to the long side of the jig. You want the transparency to 'hinge' on the tape. Take your time aligning the transparencies - this is what determines how well the pads will line up on the finished board. Thats it! To use, just tuck the sensitized board into the corner of the jig. Place into your expose frame (we use 2 pieces of glass and a vacuum pump) and expose. Turn over and expose the other side. Develop and etch. This might also work with toner transfer paper but I haven't tried it. But I suspect it would work just fine. For what its worth, we use Riston 4315 film and a modified Ibico laminator to sensitize our boards. We develop using 'soda ash' (Sodium Carbonate), etch with Ammonium Persulfate and strip the resist off with Caustic Soda (Sodium Hydroxide). The expose lamp is a 175 Watt Mercury Vapour lamp with the outer envelope removed. Its in a metal box with a motorized shutter controlled with a timer. We don't allow anyone to remain in the PCB room when the shutter is open. We've made thousands of boards over the years with extremely good results. But drilling all those holes is still a pain. dwayne PS: We asked our local University to come up with an inexpensive technique for safely disposing of spent Ammonium Persulfate etchant. They succeeded in doing so. Check with the Chemistry department at the University of Alberta. I'd be happy to pass on the technique but I'd prefer you get it from the experts. Plus - they deserve the attention and the credit. dwayne Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 17 years of Engineering Innovation (1984 - 2001) * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads