Homebrew Double-Sided PCBs - Trace Damage

Discussion in 'General Electronics Chat' started by nDever, Feb 20, 2015.

  1. nDever

    Thread Starter Active Member

    Jan 13, 2011
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    Hey guys,

    In my struggle to perfect a double-sided PCB, I've come up on another problem.

    When I go to drill holes, the drill goes in smoothly from the top layer but breaks through the bottom layer, damaging the traces/pads.

    Any insight or suggestions for getting a clean hole on the top and bottom layers?
     
  2. mcgyvr

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    Use a backerboard directly under the PCB..
     
    ErnieM and nDever like this.
  3. nDever

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    Jan 13, 2011
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    Thanks!
     
  4. nDever

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    Jan 13, 2011
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    So the other day, I tried to put a piece of hardwood behind my board as I was drilling, and I still got burrs on the other side. Will I get better hole quality with carbide bits made specifically for PCB assembly?
     
  5. jpanhalt

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    A PCB contains glass and dulls HSS bits quickly. Carbide will stay sharp longer. Are you using fast enough rpm? Too slow an rpm causes you to sort of push through and damage the back side. I just use carbide and a backer block, but I don't take care to ensure the backer block (a piece of hard wood, like birch or maple) is held tightly against the board or doesn't already have a hole under the hole I am drilling.

    The variables are speed, sharpness, and amount of push.

    John
     
  6. GopherT

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    Nov 23, 2012
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    Spin the bit fast (there are cutting edge speed recommendations all over the net if you search). Flute type, plastic type, depth all make a difference.
    Remember, if you set for a 0.050" hole and then go to a 0.030" hole, your cutting edge speed drops by 40%, so goose the speed.

    Also, in plastic, if you don't push the bit in hard enough, the plastic will melt and leave a ridge on top or bottom or melt the board/copper bonding interface. If you push too hard/fast, you break bits and/or rip through the last tents of a mm of plastic.

    Clamp the pcb to a backer board with black binder clips. Also, smooth the backer board after each use (to keep it smooth and tight to the next board you clamp) until it is too chipped up to be useful. 1/4" MDF works well for backer (and it is cheap).
     
  7. mcgyvr

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  8. jpanhalt

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    I agree about sending double-sided boards off.

    I have two boards that are about ready to send off. The trick with some vendors is the quote is based on 5 cm x 5 cm versus 25 cm^2. Both boards are small, and one will probably fit the 5X5 limit. That will give me a chance to compare vendors that I am looking forward to. Two weeks total TAT is not that bad.

    John
     
  9. nDever

    Thread Starter Active Member

    Jan 13, 2011
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    I am using my max RPM which I think is 3070.
    Shouldn't the block be firm against the board to ensure that edges don't get pushed through?

    @ GopherT,

    Thanks, will pick up some MDF from Home Depot.

    Will have to resort to this if things don't go well, but I'm determined to get this right.
     
  10. GopherT

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    The local store cut a 24 x 48 panel into a bunch of 8 x 8 inch squares for me on a dull night since he had nothing better to do.
     
  11. nDever

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    Jan 13, 2011
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    I don't think the employees at our store are that creative...
     
  12. jpanhalt

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    I truly don't think the problem is the backer board. Sure, if you clamp the pcb to the backer really, really hard, and you have a conformal solid surface on the backer, it will prevent the problem the OP has. BUT, like brass, copper will "hog in," not nearly as bad as brass, though, assuming it is not work hardened. That is, the action of proper drilling will pull the copper toward the FR4, not push it away. The TS needs a sharp bit, the proper speed, and the correct pressure. I would make a gentleman's wager that I could drill the same boards without a backer and without problems.

    John

    EDIT: I just occurred to me. Are the holes you are trying to drill etched so there is no copper in the very center?
     
    Last edited: Feb 24, 2015
  13. GopherT

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    The OP described his problem as "break through", not hogging in. Likely the biggest problem is too much pressure coupled with too slow of drill speed. An MDF backer is not likely going to help unless he properly modulates his pressure. Steel or aluminum backer may have been a better backer recommendation for someone with a heavy hand.
     
  14. mcgyvr

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    gee guys DIY PCBs would be so much cheaper if it wasn't for this unobtainium backer board I have to buy for this alien hand of mine :)
     
  15. jpanhalt

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    I agree with you up to the point of using a metal backer. The ONLY reason I use a backer to to prevent drilling thousands of little holes into my drill press's table. Pure copper is one of the more difficult materials to machine, as you know. It work hardens easily.

    I hope he will respond with regard to my question of etched copper where the tip of the drill penetrates the bottom side.

    John
     
  16. nDever

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    Jan 13, 2011
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    Sorry it took a while to respond. I don't etch the board until after I've drilled holes, so yeah, there is copper on the other side of the board when I drill holes. The reason I do this is because I can easily fix places on the board where I've missed the hole; I can use an etch resist marker. It's hard to do that with no copper.
     
  17. jpanhalt

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    And that is the sequence used by commercial vendors with expensive CNC equipment and very high speed drills with controlled feed rates. On the upside, you have lots of copper, so that should help prevent the delamination you are seeing. On the down side, the most difficult part of drilling is getting the bit started.

    Since you have maxed out on your speed, at this point, get some re-sharpened carbide drills and see if that helps. Are you in the USA?

    John
     
  18. nDever

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    Jan 13, 2011
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    Yes. West coast--Virginia to be exact. We have a local Harbor Freight not too far away.
     
    Last edited: Feb 24, 2015
  19. jpanhalt

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    PM me with your mailing address, and I will send a few of the resharpened drills I use. They have 1/8" shanks.

    Be sure to indicate whether it should go to the Virginia on the East coast or the West coast of the US.

    John
     
  20. nDever

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    Jan 13, 2011
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    Apparently I don't know where I live. Sorry, that's east coast, and thanks! :)
     
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