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How easy to damage components through flow soldering?

Discussion in 'Electronic Design' started by Peter, Mar 2, 2007.

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  1. Peter

    Peter Guest

    We have just had a delivery (from a pick/place subcontractor) of a few
    thousand populated circuits.

    Each one has a 22uF 50N Nichicon aluminium electrolytic cap on it, SMT
    type.

    I immediately noticed that all the caps have their top slightly bowed
    outwards.

    So I applied a 370degC temperature controlled soldering iron to the
    case of a fresh one of these. After a long time, after the cap was
    smoking away quite a bit, the top of it did indeed come up. Eventually
    it came up a lot more than those on the PCBs... yet, it still measured
    22uF-23uF with a capacitance meter.

    I am going to visit the contractor on Monday to see if we can work out
    what they did with their reflow oven to cause this.

    What concerns me is whether I should scrap all the circuits as a
    precaution. If I did that, what legal basis would I have for doing
    that? It would be hugely expensive, about US$20k.

    The rest of the components are some SO-14/16 chips, HP optoisolators,
    loads of ceramic caps, 0805 mostly but some bigger, melf (glass)
    diodes, plastic power diodes, etc.
     
  2. Brian

    Brian Guest

    Reply by email, perhaps I can help.
     
  3. Peter

    Peter Guest

    Reposted with my email address.

    Peter.
     
  4. Guest

    Do they work?? The ones I use look like that from the factory!
     
  5. Brian

    Brian Guest

    How'd it go at the manufacturer? We do quite a bit of lead free now. I
    know many manufacturers attacked it first by throwing lots of heat at
    it, NOT the way to go. Yes, I know Rohs is Bull-oni, but if you have
    to do it, might as well do it a best you can.

    Don't know if this is the problem in your case. hope you solved it.

    Brian
     
  6. Peter

    Peter Guest

    I got a bit further now. The contractor had (without authorisation)
    reflowed that job using his lead-free oven profile, which is about 35C
    hotter. The temp profile is *just within* the published profile for
    that Nichicon capacitor (exceed 230C for 30s max, and 250C max) so I
    suspect the caps will actually be OK. They measure OK. I am waiting to
    hear from Nichicon for a confirmation; I sent them the oven profile.

    Their initial informal view was that a bit of gas pressure doesn't
    matter, so long as the thing doesn't blow apart...

    OTOH we do all remember that business from a couple of years ago when
    PC motherboard capacitors were "inflating" themselves all over the
    place, and losing their properties in the process. I think the cap
    value was OK but the ESR went sky-high.

    Unfortunately I can't measure ESR with anything I have here...

    The safest thing will be to rework all the circuits and change the
    caps.
     
  7. Peter

    Peter Guest

    ""
    Yes, they work.
     
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