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Thru-hole headers on SMD boards...

Discussion in 'Electronic Design' started by [email protected], Dec 11, 2008.

  1. Guest

    How are thru-hole headers with heat sensitive plastic handled during
    PCB assembly these days? Are they soldered manually after reflow?
    Basically, I'm wondering whether the board spec (drill hole diameter)
    should call for the header pins having a tight or loose fit. A tight
    fit would make the manual soldering process easier IMO.
     
  2. Through hole parts are normally flow (wave) soldered, as a separate
    production process. With the plastic part of the header on the
    opposite side of the PCB from the solder wave, of course. Normal
    plastic headers will take this amount of heat without melting - that
    is how they are designed to be soldered. They don't float up in my
    experience.
    The through hole ones are much, much cheaper. Stronger too.
     
  3. I'm thinking of the "standard" single or dual row 0.1 inch pitch,
    0.64mm(?) square pin types here. They were about $0.003 per pin last
    time we bought a load. I have never had any quality problems with the
    ones we get. Not sure whose they are right now but they were bought
    from a largish UK distributor. The SMT connectors I have looked at
    have been a lot more expensive, although of course it can save an
    extra production step.
     
  4. Guest

    That's what we do.

    Me too. But the headers fit so loosely when the board is made to the
    manufacturer's (Molex etc.) header spec that it's a PITA to solder.
     
  5. Guest

    Through hole parts are normally flow (wave) soldered, as a
    I know but what do they do when the board is predominantly SMD? Video
    boards in particular tend to have SMD components on both sides.
     
  6. Guest

    I'm thinking of the "standard" single or dual row 0.1 inch pitch,
    Breakaway headers...Yeah, they're also great for jumper pads, just
    break off the amount you need. I buy them in bulk too. Don't see
    myself designing for SMD headers anytime soon.
     
  7. krw

    krw Guest

    We use a selective solder tool for through-hole parts. It's
    basically a solder fountain on an X-Y-Z stage.
     
  8. Guest

    We use a selective solder tool for through-hole parts. It's
    Okay thanks. Do you place thru-hole headers by hand or is a thru-hole
    automated PnP used? I want to spec my boards so that headers have a
    tight fit to make manual soldering by me easier for the time being but
    wondering whether this is a no-no for say an assembly house using
    automated PnP machines and something like the solder fountain you
    mention. Following say Molex's spec for the header holes results in a
    very loose fit and I'm wondering if there is a good reason for it.
     
  9. Guest

    I have used a piece of foam and also just some cloth on the headers.
    Yes, that works but the easiest route is smaller holes allowing the
    headers to remain in place by themselves. IIRC, .033" holes instead
    of .035" does the trick for my boards. Pins are square so solder flow
    along and around the boards thru-hole plating is not an issue.
    Wondering what are the downsides associated with a tight fit.
     
  10. krw

    krw Guest

    It needs a .200" component keepout area on the reverse side, around
    the thru-hole components (thru-hole components can be closer to
    each other).

    BTW, it's fun to watch. ;-)
     
  11. Guest

    Wondering what are the downsides associated with a tight fit.

    Should also mention that the tolerances that I've encountered do not
    justify such a loose fitting. Seems to be overly conservative IMO.
     
  12. Blu-Tack.
     
  13. I have seen a guy doing this with the main solder wave!

    Scary - it was bad enough when I got hot melt glue on my finger.
     
  14. krw

    krw Guest

    I think they're placed by hand, but I don't go back there very
    often. There aren't very many thru-hole parts (connectors and
    transformers, mainly).
     
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