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Paste in Hole Process

Discussion in 'Electronic Design' started by Boris Mohar, Mar 9, 2009.

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  1. Boris Mohar

    Boris Mohar Guest

  2. Eeyore

    Eeyore Guest

  3. Boris Mohar

    Boris Mohar Guest

    Not to take leaded components but to save space and drop the impedance down
    for better decoupling. Via in a smt pad was a no-no. Paste would squeeze
    through the hole and make a mess on the other side.
  4. TheM

    TheM Guest

    I thought the problem was that tin was sucked into the via hole leaving pad too dry to
    form a good connection with the component? That's what I've seen on my early boards
    where I actually placed a few vias on pads. Haven't seen it come out on the other side.

    I'd expect this to be less of a problem with lead-free soldering, seems not to
    "flow" as easily as good old lead stuff so a small via vould probably work.

  5. That was my interpretation too. It would be nice to put a via in every
    BGA pad, to make them accessable for test. But you don't want the ball
    vanishing down the hole...
  6. Guest

    That was my interpretation too. It would be nice to put a via in every
    I did this accidentally with lead free solder. The ball disappeared
    on every board. Fortunately it was a prototype run, so it was
    possible to recover the boards by pushing a fine steel wire through
    the via to make contact with the underside of the BGA.

  7. Capillary action tends to suck out the solder and even balls on BGA.
    I have seen guidelines that capping the via with solder mask from the
    back side tends to prevent that, but is not reliable enough. Filling the
    via is possible but troublesome, so the recommendation was to avoid
    in-pad vias.
  8. TheM

    TheM Guest

    Ok, good to know.

  9. YD

    YD Guest

    Late at night, by candle light, przemek klosowski
    I saw somewhere mentioned that with a fine enough drill the vias will
    plate shut. OTOH you'll have to talk nicely with the boardhouse since
    they don't appreciate it much.

    - YD.

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  10. Nico Coesel

    Nico Coesel Guest

    Actually, many SMT power components have a thermal pad these days. It
    is often recommended to put vias in the thermal pad for better heat
    distribution to the ground layer. Another use for these vias is to be
    able to hand solder the thermal pad from the opposite side of the
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