Post by thread:[OT:] Homebrew DS pcb

On Wed, 3 Mar 2004, Hulatt, Jon wrote: > Previously I've mostly made SS pcb's at home with very good results. Last > couple have been double sided, but I'm still having problems getting the 2 > sides properly aligned. My last effort was "good enough", but I'm still > destroying half of the pad on the opposite side when I drill the really > small pads (like for my 4 vias). I'm about to branch into the double-sided world too, and I was thinking of printing out the overlays with cross-hairs out of the boards' area, then taping (or stapling) the two transparencies together to form an envelope using the cross-hairs for alignment. Then you could pop the board into it and tape it so it can't move. Well, it seems to work OK in my head anyway :) Cheers, Tim -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

That's about what I do. In fact, I don't even put cross hairs on it. I simply use the holes from through hole parts to line things up and then tape the two transparency sheets together to form the envelope. The only time this method hasn't worked for me is when I was careless inserting the PCB into the envelope. If you imagine the side profile of the PCB, you need to make sure the tape joint is half way between the top and bottom of the PCB. It is easy for the transparencies to slide so that the tape joint is at the top or bottom, causing the layers to be slightly offset from each other. You could probably minimize that problem by using the biggest transparency size you can. I was limited by my 6" x 6" glass sheets that I use to hold the transparency flat to the PCB during the exposing step. So yeah, this method isn't guaranteed to be super accurate, but with a little care it can produce very nice, well aligned double sided PCBs. Eric On Wed, 3 Mar 2004 09:08:20 +0000 Tim ODriscoll <spam_OUTtimTakeThisOuTSTOKEPOGESWAY.NET> wrote: {Quote hidden}> On Wed, 3 Mar 2004, Hulatt, Jon wrote: > > Previously I've mostly made SS pcb's at home with very good results. Last > > couple have been double sided, but I'm still having problems getting the 2 > > sides properly aligned. My last effort was "good enough", but I'm still > > destroying half of the pad on the opposite side when I drill the really > > small pads (like for my 4 vias). > > I'm about to branch into the double-sided world too, and I was thinking of > printing out the overlays with cross-hairs out of the boards' area, then > taping (or stapling) the two transparencies together to form an envelope > using the cross-hairs for alignment. Then you could pop the board into it > and tape it so it can't move. > > Well, it seems to work OK in my head anyway :) > > Cheers, > > Tim > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On Wed, 3 Mar 2004 08:49:35 -0000, you wrote: >Previously I've mostly made SS pcb's at home with very good results. Last >couple have been double sided, but I'm still having problems getting the 2 >sides properly aligned. My last effort was "good enough", but I'm still >destroying half of the pad on the opposite side when I drill the really >small pads (like for my 4 vias). > >I use presensitised board, and laser printed transparency and a homemade UV >box. > >How do other people align the transparency on either side? > >jon Staple the 2 artwork sheets together to form an envelope, into which you insert the PCB. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

pic microcontroller discussion list wrote: > How do other people align the transparency on either side? Others have mentioned the 'pocket' method. I've used it, and it works for small PCBs. The following method may sound complicated, but it really is not. Hope I explain it clearly enough. Maybe it will spark ideas for improvement. I cut two thin sheets of plexiglass such that the width is always less than my PCB, but the length is always greater than my pcb (say like 2" by 12"). The two sheets were taped together. Using a drill press, drill three holes for 1/4 screws. Now the two sheets can easily be aligned. One artwork transparancy is attached (taped) to one of the plexiglass sheets so it cannot move. the second is loose. Assemble the plexiglass and position the second artwork so they line up. Secure the second artwork to the second plexiglass. Now loosen the screws so that you can slide your PCB in between. tighten screws, secure the artwork to the PCB; then remove the plexiglass, leaving the artwork aligned and attached to the PCB. This method requires the artwork to be smaller than the actual PCB, but larger than the plexiglass frame so it can be attached. It's sufficient if the length or width of the artwork is smaller; that's why the frame is long and skinny. The above procedure could be simplified if the plexiglass were replaced by glass; I'm thinking of a plexiglass "frame" that could be aligned as described above. this frame would hold the glass in place. Now only the artwork would have to be larger than either the length or width so the two sides can be aligned. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On Wednesday, Mar 3, 2004, at 05:41 US/Pacific, Anthony Toft wrote: >> How do other people align the transparency on either side? >> You COULD drill some of the holes first, put more holes in your transparencies, and run registration pins/wires through the whole sandwich. But I think even with perfect registration, you're somewhat likely to push the bottomside pads off during drilling. Try larger pads (if you're in control of that. that's one of the defaults i change all the time in eagle...)? BillW -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

pic microcontroller discussion list wrote: > How do you manage plexiglass bending in the middle of the pcb? that's why the plexiglass is removed afterwards: >> Now loosen the screws so that you can slide your PCB >> in between. tighten screws, secure the artwork to the >> PCB; then remove the plexiglass, leaving the artwork >> aligned and attached to the PCB. I use the normal glass/foam frame for exposure afterwards. I thought it was obvious, having done it so many times. sorry that this wasn't more explicit. The plexiglass is only used to align the top/bottom artwork onto the PCB. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Hulatt, Jon wrote: > Previously I've mostly made SS pcb's at home with very good results. Last > couple have been double sided, but I'm still having problems getting the 2 > sides properly aligned. My last effort was "good enough", but I'm still > destroying half of the pad on the opposite side when I drill the really > small pads (like for my 4 vias). > > I use presensitised board, and laser printed transparency and a homemade UV > box. > > How do other people align the transparency on either side? > What about drilling the holes in the pcb before etching? Of course it is easier if you have access to NC machine but here is a possible method if you don't. 1) Print the holes layer of your pcb on a sheet of paper; 2) spray a thin coat of artist glue onto the copper clad and lay the sheet of paper without any wrinkles and air bubbles; 3) drill all the holes; 4) Clean the paper off the clad. I have used this method for folding metal sheet to make prototypes and it works great. Let me know how it works for holes. Gaston -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

At 01:49 AM 3/3/2004, Hulatt, Jon wrote: >Previously I've mostly made SS pcb's at home with very good results. Last >couple have been double sided, but I'm still having problems getting the 2 >sides properly aligned. My last effort was "good enough", but I'm still >destroying half of the pad on the opposite side when I drill the really >small pads (like for my 4 vias). I use a piece of PCB material cut into the shape of a carpenter's square. Think of a large "L" about 6" tall with a 4" leg. The material is about 1" wide. I make mine from the the same type of PCB material that I am exposing: un-etched double sided board. I want it to be the same thickness or just a smidgen thinner (its thinner by the thickness of the photo-sensitive laminate). Tape one of the transparencies to both legs of the "L". Make sure to position the transparency so as to leave a border of scrap material on the finished board. In other words, don't position the transparency so that it is exactly on the edge of the holder. I set mine up about 3/16" or 1/4" inward (the boards are cut about 1/2" larger than the finished size). Now flip the whole thing over and place it on a light table. Carefully line up the other transparency and tape only one edge to the long part of the "L". Check the alignment again. Then make sure the transparencies are not reversed! Flip open the holder, drop in the PCB and push it tight into the corner of the "L", close it and put the whole thing into your exposure frame. The main reason for taping only one edge of one of the transparencies is that they stick to the PCB after exposure. That is - they stick when I expose boards in my setup (175 W Mercury vapor bulb with outer glass envelope removed, vacuum frame running at about 15" of mercury vacuum level). Since only one edge is taped on one piece, you can peel that one off the board first, then peel the board out of the holder and off the other transparency. The registration doesn't shift if you are careful. My exposure frame is made from 1/4" glass. I line the edge of the bottom piece of glass with a soft, airtight adhesive weatherstrip. The top piece has a 3/8" hole drilled in one corner - just inward of the weatherstrip. There are rubber feet on both the bottom and top pieces - I can just flip the whole frame to expose the other side of the PCB. The vacuum source is an old beat-up Gast vacuum pump. My expose distance is 13" and the expose time is about 130 seconds per side as determined with one of those graduated exposure calculator strips. Hope this helps! dwayne -- Dwayne Reid <dwaynerKILLspamplanet.eon.net> Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 20 years of Engineering Innovation (1984 - 2004) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' 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: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics