ddurbin@polyslo.CalPoly.EDU (Daniel A. Durbin) (04/08/89)
There was some discussion a while back concerning the transfer of the toner from a laser printed transparency of a PCB layout to the actual copper of the PCB to be etched. A friend of mine has tried this but has had trouble getting a good transfer efficency of the toner to the copper. This subject was discussed in follow-ups to an article on PCB production, but I missed all of it. If someone has a transcript of those discussions or an efficient method of transfer, please forward them to me. Thanks in advance. Daniel Durbin___________________________________________________ SysOp: Cygnus X-1 BBS | CIS: 73447,1744 (805) 541-8505 (data) | GEnie: D.DURBIN EL major at PolySlo | ddurbin@polyslo.CalPoly.EDU
ddurbin@polyslo.CalPoly.EDU (Daniel A. Durbin) (04/11/89)
I would like to thank all who have sent responses to my inquiry about the discussion that took place about PCB's using transparancies. I would especially like to thank Kevin Kenny who sent me what appears to be a complete transcript of the discussion. The transcript is very long, so I didn't included it in this posting, but I will email it to anyone who is interested. If enough interest is presented, I will post it as an article. Daniel Durbin___________________________________________________ SysOp: Cygnus X-1 BBS | CIS: 73447,1744 (805) 541-8505 (data) | GEnie: D.DURBIN EL major at PolySlo | ddurbin@polyslo.CalPoly.EDU
ddurbin@polyslo.CalPoly.EDU (Daniel A. Durbin) (04/12/89)
The following is what seems to be a complete transcript of the discussion that took place a while back concerning using transparencies to etch PCB's. I am posting this since the response I received was overwhelming. If anyone has additional information or an improved proceedure, I would be very interested in hearing about it. Thanks to all for responses. Daniel BEGIN discussion ---------------- From kenny%f.cs.uiuc.edu@a.cs.uiuc.edu Mon Apr 10 11:43:30 1989 Received: from A.CS.UIUC.EDU by polyslo.calpoly.edu (5.61/1.881115) id AA16359; Mon, 10 Apr 89 11:41:33 -0700 Received: from f.cs.uiuc.edu by a.cs.uiuc.edu with SMTP (UIUC-5.52/9.7) id AA17292; Mon, 10 Apr 89 12:39:18 CST Received: by f.cs.uiuc.edu (UIUC-5.52/9.7) id AA24304; Mon, 10 Apr 89 12:39:05 CST Date: Mon, 10 Apr 89 12:39:05 CST From: kenny%f.cs.uiuc.edu@a.cs.uiuc.edu (Kevin Kenny) Message-Id: <8904101839.AA24304@f.cs.uiuc.edu> To: ddurbin@polyslo.CalPoly.EDU Subject: PCB's using transparancies Status: R /* Written 3:57 pm Apr 7, 1989 by ddurbin@polyslo.CalPoly.EDU in m.cs.uiuc.edu:sci.electronics */ /* ---------- "PCB's using transparancies" ---------- */ There was some discussion a while back concerning the transfer of the toner from a laser printed transparency of a PCB layout to the actual copper of the PCB to be etched. A friend of mine has tried this but has had trouble getting a good transfer efficency of the toner to the copper. This subject was discussed in follow-ups to an article on PCB production, but I missed all of it. If someone has a transcript of those discussions or an efficient method of transfer, please forward them to me. Thanks in advance. Daniel Durbin___________________________________________________ SysOp: Cygnus X-1 BBS | CIS: 73447,1744 (805) 541-8505 (data) | GEnie: D.DURBIN EL major at PolySlo | ddurbin@polyslo.CalPoly.EDU /* End of text from m.cs.uiuc.edu:sci.electronics */ OK, here's the stuff. < Written 2:38 pm Jan 13, 1989 by kenny@m.cs.uiuc.edu in sci.electronics > < ---------- "Thermofax for PC negatives?" ---------- > I've got a question about PC board fabrication. The major cost of producing a PC layout is the artwork, of course. One thing that I've been tempted to do is to produce a (negative) etching template on a PostScript engine, on paper. A film negative can then be produced using a ThermoFax [1] machine, and the photoresist exposed through this negative. I've already done the first stage of this -- producing board artwork in PostScript (Don't ask about the software -- it's a hideous kludge, and I'm not willing to put in the effort right now to get it to the point where anyone else could use it). With careful tweaking of the `scale' operator, I can overcome aspect ratio problems on the printer (at least on the Imagen I'm using -- a desktop model might have problems with nonlinearity in positioning) and place the image within acceptable dimensional tolerances. Has anyone any experience with exposing photoresist through ThermoFax film? Is the film sufficiently transparent to UV (in the clear areas) and sufficiently opaque (in the dark areas) to make the photoresist take a good image? I'm willing to do touchup work with opaquing ink (for holes in the black areas) and an X-Acto knife (for specks), but I would prefer to avoid nasty surprises. If it's feasible, this would seem to be a really neat technique, particularly for basement operations; most schools have a ThermoFax machine or two somewhere. I'd be surprised if someone out there hasn't tried it already. Comments? Pitfalls that I'm overlooking? -------------------- [1] ThermoFax is a process for producing overhead transparencies. There is no problem with aspect ratio control, as there might be with the technique of photocopying onto acetate, because ThermoFax is a contact printing process. Kevin Kenny UUCP: {uunet,pur-ee,convex}!uiucdcs!kenny Department of Computer Science ARPA Internet or CSNet: kenny@CS.UIUC.EDU University of Illinois 1304 W. Springfield Ave. Urbana, Illinois, 61801 Voice: (217) 333-6680 < End of text from sci.electronics > < Written 6:16 am Jan 14, 1989 by w-colinp@microsoft.UUCP in sci.electronics > Some fellows at the University of Waterloo hardware lab managed to stick a resist pen onto a flat-bed plotter. Now, they just stick in some plastic- coated copper :-) and let it run. Into the etch, and presto! I didn't ask, but i'd think the plotter would have adequate repeatability to do 2-sided boards. -- -Colin (uunet!microsof!w-colinp) < End of text from sci.electronics > < Written 7:36 pm Jan 14, 1989 by gbell@pnet12.cts.com in sci.electronics > I've had some experience developing PC boards from Xerox copies... with some heating, and a few tricks, the toner on a transparency copy of your artwork can be applied to a copper board. It then hardens and acts as an excellent etch-resist. A few companies are trying to perfect this method and market it... but I've had some good results as an experimenter. Let me know if you're interested, and I can E-Mail you an article I wrote. Or, if there's sufficient interest here, I'll post it. Greg Bell_________________________________________________________ Hardware hacker | Electronics hobbyist | UUCP: uunet!serene!pnet12!gbell EE major at UC San Diego | < End of text from sci.electronics > < Written 3:48 pm Jan 16, 1989 by craig@hp-lsd.HP.COM in sci.electronics > > Or, if there's sufficient interest here, I'll post it. You've got one vote. Craig McCluskey HP Logic Systems Division Colorado Springs, CO < End of text from sci.electronics > < Written 4:36 pm Jan 16, 1989 by gbell@pnet12.cts.com in sci.electronics > < ---------- "PC Boards using Transparencies" ---------- > Wow! I got about 14 E-Mail requests for the article I wrote! I E-Mailed a few responses before I realized it would be much easier to just post it. Maybe the word "article" is misleading. What I wrote is simply a document of what I know about the method. Personally, I prefer wire-wrapping for prototyping, but this method has potential. In fact, a few companies are trying to making this method a commercial product. Anyway, here's what I've got. Please let me know what you think, any questions you have, and any experience you gain trying out the method... ########################################################################### Making PC Boards Using Xerox Transparencies This method is not perfect, but its simplicity makes it worth trying. I have successfully made a few simple PC boards using this method and have tried a more complicated board. Due to a design error with the complicated board, I never figured out whether the circuit board was OK (I ended up wire wrapping the thing). The beauty of this method is that you can create the artwork for the board using regular pens and drafting supplies- much as you would be able to for the standard photographic technique. This is welcomed by those of use who have tried to use etch resist pens or lacquer. The cost of making boards this way is much cheaper than regular photographic techniques. Make sure all lines on the finished artwork are as black as possible (use black ink). The artwork must be Xeroxed onto transparency plastic. Beware! You can NOT use just any kind of clear plastic sheets. The temperature inside a Xerox machine will melt most plastics and ruin the machine. There is a specific type of plastic made just for Xeroxing things onto transparencies. I got a pack of 25 sheets for $14 at my university's bookstore. There are different types of this stuff, and some types work better than others. I was fortunate in that I was able to try out a few sheets of different types before I bought an entire pack. The types that don't work too well have an extra layer of thin plastic laminated onto the thicker sheet of transparency. This is not apparent until later in the process. You might be able to tell by looking at light reflecting off the surface of the transparency- both sides should be shiny. If one side is shiny, and one side is somewhat dull, then chances are the sheet is of the laminated type. Perhaps these types of sheets would work if you Xeroxed onto the shiny side but I haven't bothered to experiment with this. Once you have located the right kind of transparency (or have decided to try whatever transparency plastic you could get), Xerox your artwork onto the transparency with the machine set at its darkest contrast. This assures that the most toner gets deposited onto the plastic. Its a good idea to make more than one copy as a backup. Another tip: try Xeroxing onto paper first to see what the image quality is like. If the image looks less than acceptable, try another machine. When a Xerox is made onto paper, the porous surface of the paper absorbs the toner. But, on the transparency plastic, the toner can be removed... The next step requires a vise and a clothes iron. Set the iron to a moderately high temperature (again, there is a lot of room for experimentation here). Mount the bare circuit board (cleaned well with steel wool) vertically in the vise so that you have access to both sides. Cut the circuit image out of the transparency and line it up on the copper board. Tape the plastic's edge to the board's edge so that you have a hinge of sorts (masking tape is best). You should be able to lift the plastic up like a book cover, and be able to put it back down against the board without the image shifting. I have used double sided circuit boards every time I have used this method, even though I was making a single sided board. Reason: I'm not sure if the non-metal side of the board will hold up to the iron's heat (I haven't tried because I didn't want to ruin the iron). I suppose its possible to heat the board from the one metal side. I have not tried making a double sided board. The only difficulty I anticipate is in lining up the two sides' images so that the holes will match up. The copper must be heated to a high enough temperature to re-melt the toner. I have had success, like I stated above, heating the board from behind while I press the transparency plastic hard against the front part of the board. I use a bundled up rag to press against the copper since it gets VERY hot.. Press the plastic against the board using a "smoothing" wiping away from the tape hinge. Continue this for a couple minutes. The time is a big variable - too short of a time and the toner won't melt. Next, carefully start to peel the transparency from the board. Do this SLOWLY. If you see some of the toner lift off, you can put the plastic back against the board and continue heating/smoothing. Eventually you should be able to get the plastic off and a nice sharp black image of your circuit will be left behind on the copper, most of the toner should come off the transparency. If the transparency is laminated, chances are that the layers will separate at some time during this stage. In my case, the transparency left the thin layer of plastic on the copper, and it was a hassle to get it all removed. Don Lancaster, of CMOS Cookbook, TTL Cookbook, and Radio-Electronics fame (Hardware Hacker column) suggested to me that the board be placed in a freezer for a while after the plastic is removed to "fuse" the toner. If the image looks pitted in some areas, touching up the lines may help. An etch-resist pen might work, or lacquer could be used. Finally, etch the board using standard etchant. The toner makes an excellent etch resist (ie. it doesn't dissolve). When the board's finished, the toner can be removed using many different solvents. Let me know what experiences any of you have with this. I'm especially interested in tips and success/failure stories. I can be reached on USENET or on the Circuit Cellar BBS at 203-871-1988. By the way, I first read this idea in a letter in Radio-Electronics. Don't bother trying to look up the original letter because it wasn't very long or detailed. Greg Bell serene!pnet12!gbell ############################################### for a better return address, see my sig below... Incidentally, I need to find out what brand/part number the particular transparency plastic I use is. But I don't have the package here, so I will post that information when I get it. Greg Bell_________________________________________________________ Hardware hacker | Electronics hobbyist | UUCP: uunet!serene!pnet12!gbell EE major at UC San Diego | < End of text from sci.electronics > < Written 2:39 am Jan 17, 1989 by smadi@rlgvax.UUCP in sci.electronics > In article <308@serene.UUCP> gbell@pnet12.cts.com (Greg Bell) suggest an ingenious way to fabricate short runs of PCB. He uses a copying machine to transfer the artwork onto an OHP transparency, then irons it onto the PC board. The transfered copier toner acts as an etch-resist. A suggestion: Use a laser printer to generate transparencies. This works great with Apple LaserWriters(tm). MAKE SURE YOU USE COPIER-SAFE MATERIAL. And a query: Using manual feed, NEC machines can print on rather thick material. Will they print directly on thin PCB? Unfortunately* I have no access to one; otherwise I'd try it on thin material and smooth the edges to save the printer drum from scratches. Has anybody tried this? * My bad luck may have just saved a $3k printer... On (just a guest of ...!uunet!rlgvax!smadi) Paradise < End of text from sci.electronics > >From rlgvax!smadi@uunet.UU.NET Wed Jan 18 12:23:47 1989 Date: Sat, 14 Jan 89 05:57:42 est From: Smadi Paradise <rlgvax!smadi@uunet.UU.NET> To: uunet!kenny%m.cs.uiuc.edu@uunet.UU.NET Subject: Re: Thermofax for PC negatives? Newsgroups: sci.electronics In-Reply-To: <21000005@m.cs.uiuc.edu> Organization: Computer Consoles Inc, Reston VA 22091 Cc: In article <21000005@m.cs.uiuc.edu> you write: > > A film negative >can then be produced using a ThermoFax [1] machine, and the photoresist >exposed through this negative. Most printers can produce transparancies directly on OHP material. Use only sheets made FOR PHOTOCOPIER USE, as conventional seets would melt and DAMAGE THE PRINTER FOR GOOD. Boxes of the right stuff are clearly marked, and should be <$40 for 100 sheets. It seems to be very tough Mylar(tm), which can whistand the temperature and is probably transparent to UV. I used this quite a lot (along with a troff macro package) to produce slides for lectures. Playing with the ``dark/bright'' knob, you can deposit a fair amount of toner. I have no idea if this is UV opaque, but please summarize to this group when you find out. Synergetics sells PostScript printed circuit software for $40. I have no idea what is it like, but their address is: Synergetics Box 809B Thatcher, AZ 85552 (602) 428 4073 Good Luck! On >From haynes@ucbarpa.Berkeley.EDU Wed Jan 18 12:23:57 1989 Date: Sat, 14 Jan 89 12:13:48-0800 From: haynes@ucbarpa.Berkeley.EDU (Jim Haynes) To: kenny@cs.uiuc.edu Subject: PC artwork I've been looking for an article I'm sure I read, probably in Radio-Electronics and the author was probably Bruce Snow. He said after you get the artwork done, make a transparency on an office copier (not Thermofax). Then you can use an iron, he says, to tranfer the black stuff from the transparency to the copper, and use it directly as a resist. Now I can't find the article. >From aplcen!osiris!consult@mimsy.umd.edu) Thu Jan 19 22:52:33 1989 Date: Thu, 19 Jan 89 13:33:50 EST From: aplcen!osiris!consult@mimsy.umd.edu (Unix Consultation Mailbox (Phil)) To: m.cs.uiuc.edu!kenny@mimsy.umd.edu Subject: Re: Thermofax for PC negatives? Newsgroups: sci.electronics In-Reply-To: <21000005@m.cs.uiuc.edu> Organization: The Johns Hopkins Hospital, Information Systems In article <21000005@m.cs.uiuc.edu> you write: >The major cost of producing a PC layout is the artwork, of course. >One thing that I've been tempted to do is to produce a (negative) >etching template on a PostScript engine, on paper. A film negative >can then be produced using a ThermoFax [1] machine, and the photoresist >exposed through this negative. Why not put transparency stock in the PostScript engine? LaserWriters will print on it, and your Imagen should too (still using those old beasties there, huh?). Set the transfer function to invert black/white, or just hack the generating program so it draws the right areas (resist or expose) in black, depending on the emulsion you're using (you can get positive emulsions, too). >Has anyone any experience with exposing photoresist through ThermoFax >film? Is the film sufficiently transparent to UV (in the clear areas) >and sufficiently opaque (in the dark areas) to make the photoresist >take a good image? This is why I'd be tempted to to print the transparency directly.. I haven't done it, but I would not trust the thermofax film to be contrasty enough to give good exposures. The transparency film *should* be contrasty enough, and you can always screw with the printer's blackness setting if it's not (something you can't do with thermofax). I've also thought much about using this technique (with transparency film in the PostScript printer) to do color screen printing from digitally generated or scanned images. It would be pie to produce a negative for exposing a film emulsion, although the largest image size is not as big as I'd like on a LaserWriter... Phil Kos >From osiris!consult@aplcen) Mon Jan 23 12:31:30 1989 Date: Mon, 23 Jan 89 11:20:43 EST From: osiris!consult@aplcen (Unix Consultation Mailbox (Phil)) To: kenny@m.cs.uiuc.edu Subject: Re: Thermofax for PC negatives? I must only have had exposure (no pun intended) to really cheap Thermofax equipment. Hope yours works out OK. As for the durability of LaserWriters, we've found it's pretty good.. granted we don't go through a dozen reams of paper a day per printer (even when I was at UofI in '82 they thrashed that old Imagen like nothing) but we haven't had one die yet, and several of ours have over 300,000 sheets under their belts. If you can wait a little longer for your hardcopy, we've found them to be quite a good alternative. Anyway, thanks for the reply, let us know how the negatives work out... phil /* Written 11:17 am Jan 23, 1989 by rzh@lll-lcc.llnl.gov in m.cs.uiuc.edu:sci.electronics */ /* ---------- "Xerox Method of Making P. C. Boards" ---------- */ There's another potential complication in the Xerox method, I think. It has been my experience that copy machines frequently distort in one, or both, dimensions. Is this loss of 1:1 scale a problem?? It can be very difficult to notice in copying the printed page, but bothersome when copying things that need to be at the right scale (e. g. maps). Roger rzh@lll-lcc.llnl.gov /* End of text from m.cs.uiuc.edu:sci.electronics */ /* Written 2:21 pm Jan 24, 1989 by kenny@m.cs.uiuc.edu in m.cs.uiuc.edu:sci.electronics */ rzh@lll-lcc.llnl.gov writes: >[...] copy machines frequently distort in one, or both, dimensions. >Is this loss of 1:1 scale a problem?? It can be very difficult to >notice in copying the printed page, but bothersome when copying things >that need to be at the right scale (e. g. maps). That's the reason that I was discussing output from a premium laser prnter, and mentioning that I was twiddling scale factors to keep everything within tolerance. Making the transparency with ThermoFax wouldn't mess up the aspect ratio, because ThermoFax is a contact-printing process. Kevin Kenny UUCP: {uunet,pur-ee,convex}!uiucdcs!kenny Department of Computer Science ARPA Internet or CSNet: kenny@CS.UIUC.EDU University of Illinois 1304 W. Springfield Ave. Urbana, Illinois, 61801 Voice: (217) 333-6680 /* End of text from m.cs.uiuc.edu:sci.electronics */ /* Written 11:27 pm Jan 23, 1989 by gilley@goofy.apple.com in m.cs.uiuc.edu:sci.electronics */ /* ---------- "PC. boards" ---------- */ Notes: Kepro Circuit Systems, Inc. (800-325-3878) offers a cheap negative acting dry film photo resist copper clad. The development solution is a water based sodium carbonate (none of that nasty solvent stuff). I've had good luck with negative, 1:1, artwork on a laserprint transparency. One line between pin resolution. For great precision mechanical components of all types: Winfred M. Berg, Inc. (516-599-5010). They have this real neat 3-D (x-y-z) belt and sprocket product. Tom Gilley /* End of text from m.cs.uiuc.edu:sci.electronics */ Kevin Kenny UUCP: {uunet,pur-ee,convex}!uiucdcs!kenny Department of Computer Science ARPA Internet or CSNet: kenny@CS.UIUC.EDU University of Illinois 1304 W. Springfield Ave. Urbana, Illinois, 61801 Voice: (217) 333-5821