(Topic ID: 145102)

Fixing a hole in a PCB


By johnwartjr

3 years ago



Topic Stats

  • 22 posts
  • 12 Pinsiders participating
  • Latest reply 3 years ago by snyper2099
  • Topic is favorited by 7 Pinsiders

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    #1 3 years ago

    I do a lot of rework that involves eyelets, but every now and again, I get a really nice board in that has one transistor that has gone full supernova or something, and I have to try and find a way to put it back together.

    I'm curious what methods you've used to fill a hole in a PCB before rebuilding traces, vias, etc...

    Here's the one I'm working on now, but I'm not sure how I'm going to fix it yet. The board was so burnt and delaminated, the eyelets just pushed through the board...

    IMG_8341.JPG

    #2 3 years ago

    I've read that some folks use epoxy. Haven't had occasion to try it myself quite yet, though.

    #3 3 years ago

    Since the hole goes all the way through the board I would route out the area, install a new piece of circuit board using a lap joint and then install with epoxy and fill any gaps.

    http://www.circuitmedic.com/guides/3-5-2.shtml

    You could also just fill the area with epoxy. Circuit Medic has some colorants for epoxy that are pretty cool.

    #4 3 years ago

    Whatever I use has to be solid enough that I can drill it to set eyelets, and that I can hammer on the eyelet setting tools without cracking it.

    It also has to withstand heat to the point that I can solder on it. This part of the PCB does get warm during normal operation as well.

    And, it can't conduct.

    I am considering JB weld. It doesn't conduct, it is actually an insulator, will handle up to 550 degrees of heat, readily available and not super expensive.

    I'm willing to try other types of epoxy. Or other solutions. I'm going to file on the edges a bit to get rid of any other loose fibers and get as close to 'fresh' PCB as I can without compromising the remaining good traces.

    #5 3 years ago

    Yikes, that coloring agent is $15 per oz. Neat idea, though.

    #6 3 years ago

    Fiberglass epoxy resin. You can get it in the body section of any auto parts store.

    #7 3 years ago
    Quoted from johnwartjr:

    Whatever I use has to be solid enough that I can drill it to set eyelets, and that I can hammer on the eyelet setting tools without cracking it.

    The section with a lap joint will stand up to just about anything. Once you get the hang of it, it only takes a few minutes to create the replacement piece. In your case just do the lap joints on the two sides to avoid the other eyelets.

    The JB Weld should work fine. I don't think there's any magic to the other types of epoxy.

    #8 3 years ago

    Yep, fiberglass resin is good stuff.

    Trim out all that carbon though, because it's conductive.

    #9 3 years ago

    You might research "plastex", I have used it with very good results on many things but never a board.

    #10 3 years ago

    Some good feedback here.

    The 'right' way to repair the board does look really cool.

    But, what I quoted on this job makes fixing it that way unlikely this time around.

    And, in a few of the cases I see - for example, a Sys3-7 driver board with a street value around $100, the cost of the labor and materials involved might make the repair exceed the cost of the board. So, I decided to take a low budget approach on this one, and see how it turns out.

    So, I cleaned the edges up to make sure the rest of the carbon was gone....

    IMG_8346.JPG

    Masked it off (note: wax paper is underneath the hole, before the tape)

    IMG_8347.JPG

    Filled with JB Weld

    IMG_8348.JPG

    I will return back to the board in 24 hours to allow it proper time to 'set' and will give it a light sanding and try to drill the 2 .156 mounting holes for the 2 GI pins. Once it dries, I'll enlarge the holes slightly with the bit for the eyelets, and see if the JB Welded board is solid enough for the eyelets.

    Rather than copper foil, I believe I will finish this repair with a solder stitch, as I am familiar with that process, and have everything I need on-hand for that repair.

    #11 3 years ago

    I found this repair on a Stern Stampede Ball Count Unit. Traces are repaired with copper foil tape, and the holes are filled with either Epoxy or Fiberglass Resin. Its a slightly yellow color. You can see through the back and see the traces on the front, so it's semi-transparent. The new copper traces have been soldered to the old on top of the repaired areas. It was working, but I did replace it with a NOS one I found because it seemed a bit too burny for me to be comfortable with in my home.

    Epoxy_Repair_1.jpg

    Epoxy_Repair_2.jpg

    #12 3 years ago
    Quoted from johnwartjr:

    The 'right' way to repair the board does look really cool.

    A lot of the standards are oriented towards rework (to fix design flaws or manufacturing issues) rather than repair. In a rework situation the board has to look like new when you're done. People get upset when they get their brand new, multi-million dollar MRI machine and the boards look like they've been worked on before.

    Thanks for posting pictures. Look forward to seeing the end result.

    #13 3 years ago

    So, I let the JB weld dry for 24 hours. Actually, a little closer to 29 hours or so

    Carefully peeled the masking back, and sanded both sides flat.

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    Took a .156 header, and removed 2 pins. Carefully enlarged each hole in the header housing to fit a small drill bit to put a pilot hole in

    IMG_8361.JPGIMG_8362.JPGIMG_8364.JPG

    Enlarged the pilot holes to the correct diameter for the eyelet, and inserted 1 eyelet

    IMG_8368.JPG

    And, the JB weld cracked after a few taps with the tack hammer to set the eyelet.

    IMG_8370.JPG

    Looking at the situation, I wondered if maybe the JB weld is too brittle for this. But, looking at it a little closer, I don't think that's the problem. The JB weld is strong enough. The problem is, I believe I need some support around the eyelet as I set it, so the board isn't flexing while I hammer on it.

    So, I'm going to mask it off again, load it up with filler again, and let it dry for another 24 hours. Thinking perhaps I need to put a piece of hardwood under the board when I set the eyelet. Perhaps take a piece of hardwood, bore a hole big enough for the eyelet setter to slide through it, and then rest the board on it to provide support outside the actual eyelet area. Hard to describe...

    I think also, I need to sand the JB weld a bit more, and get the top and bottom of the PCB perfectly flat. The eyelets are sized to the thickness of the PCB. If the board were thinner, it wouldn't be as big an issue - but if the board is thicker, there's not enough eyelet material to create the top 'flange' when you set it.

    #14 3 years ago

    Instead of using a hammer to set the eyelet, can you use a G clamp or similar? No impact on the board/JB weld then.

    #15 3 years ago

    I thought about that, I have a set of dies/punches, and do not have any sort of clamp that I believe could rotate the dies/punches.

    The eyelets that are .156 diameter are harder materials than the smaller size as used on transistors, IC legs, etc.

    #16 3 years ago

    It is tricky. I guess anything that gets the eyelet locked in but doesn't shock the board too much will help. Another thought - how about chamfering the top and bottom of the hole in the board, so that they meet in a point halfway through? Then, the whole JB Weld plug would act like a rivet, and wouldn't be able to twist/slide out...

    #17 3 years ago

    Could you somehow set the eyelet into the wet JB Weld before it dries?

    #18 3 years ago

    another way i was told .. ( never tried it)

    cut the hole shape from green scourer pad ..

    eg http://www.scotch-brite.com/wps/portal/3M/en_US/Scotch-BriteBrand/Scotch-Brite/Products/Product-Catalog/~/Scotch-Brite-Heavy-Duty-Scour-Pad?N=4337+3294631680&rt=rud

    fit to hole .. flood with 2 pack epoxy.

    #19 3 years ago
    Quoted from wiredoug:

    cut the hole shape from green scourer pad ..

    Interesting idea.
    I have been using a fiberglass reinforced epoxy mix with ok success.

    #20 3 years ago

    2nd attempt....

    I prepped and filled the PCB, following the same process with JB weld.

    Drilled small pilot holes, then larger holes of the correct diameter

    Inserted the first eyelet, and laid a small piece of steel underneath the edge of the board, larger than the spot that was filled.

    IMG_8387.JPG

    Used a punch to set the eyelets.... and it didn't shatter the JB weld out of the hole

    Did some small solder stitches to repair the traces

    IMG_8388.JPG

    Installed a new 12 pin header

    IMG_8390.JPG

    Not a perfect looking board, but now a perfectly functional one.

    Thanks for all the advice. I would like to experiment with different epoxies. Thankfully, I've saved a few unrepairable boards to experiment with.

    1 month later
    #21 3 years ago

    Round 2..

    Burned out special solenoid transistor on a High Speed CPU.

    Filed the burnt area until the PCB was clean and not burnt. Removed any burnt components. Used a proto board lined up with the transistor on each side of the burnt area to mark the location for the 3 holes. Drilled 3 pilot holes, then stepped up to the appropriate drill for the eyelets. Set eyelets. Installed transistor and missing bits, ran a few jumper wires to replace burnt traces, voila!

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    #22 3 years ago
    Quoted from johnwartjr:

    Used a punch to set the eyelets.... and it didn't shatter the JB weld out of the hole
    Did some small solder stitches to repair the traces

    That's exactly how I repair severe damage like this. Good work!

    JB weld and a variable speed dremel are two tools that you would never think need to be in your pinball repair bin/toolbox! 100 uses for each!

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