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  1. #1
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    Bad solder joints on surface mount connector

    Hi, I have a problem with a surface mount connector. .. nearly half of the 40 pins have bad solier joint after reflow. They look OK but they fail after a few weeks (cracking). Have tried touchup by reflowing the bad joints using solder iron but the parts fail again a few weeks later. Using sn63 leaded solder. Connector pins have Ni Au flash finish. Any ideas what could be the cause?
    Thanks.

    •   Alt9th April 2017, 20:58

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    Re: Bad solder joints on surface mount connector

    They fail just sitting there, or is there something you're not telling us? Temperature cycling? Mechanical stress? Environmental?

    Perhaps inadequate cleaning before soldering.

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    Re: Bad solder joints on surface mount connector

    Inspecting the joints more closely would probably tell
    you (or more likely, a trained inspector or assembler)
    what the cause is. Whether the solder itself is cracking,
    or failing to adhere in the first place, "cold joint" etc.
    are things that people get trained to judge. I'd bet you
    could find descriptive pictures on the Web, but do you
    have the microscope, time and confidence? Or better
    to tap someone who does?

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    Re: Bad solder joints on surface mount connector

    Thanks Barry, thanks dick
    Barry,
    no deliberate vibration or temperature cycling applied. However the parts will have seen some baking at 70oC for a few hours to cure some glue used elsewhere. Actually, we try to fit a brass shell to the connector after connector is fitted and when we solder that shell in place some of the connector pin solder joints fail. Maybe heat is causing the problem ?

    Dick
    thanks. I have tried to add a photograph to see if anyone can spot whether these are cold joints or cracks.

    •   Alt10th April 2017, 23:19

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    Re: Bad solder joints on surface mount connector

    Quote Originally Posted by Jimbo7 View Post
    I have tried to add a photograph
    Sorry, no image is visible. Try the 'Add an Image' button, it's reliable and straightforward.

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    Re: Bad solder joints on surface mount connector

    If i had to guess, I'd say it's contamination. Try degreasing before soldering.

    •   Alt11th April 2017, 06:47

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    Re: Bad solder joints on surface mount connector

    Now with image added Click image for larger version. 

Name:	20170411_080826.jpg 
Views:	15 
Size:	422.6 KB 
ID:	137774

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    Re: Bad solder joints on surface mount connector

    To my untrained eye (one that has only seen plenty of
    my own work) it looks like the joints were moved while
    still (partially) molten, crystallized ("cold") rather than
    shiny, dragging material and developing voids as a result.
    Might look to the fixturing of the upper piece and the
    thermal ramp rates, keep things firmly in place until the
    assembly has truly solidified.

    Might need more than gravity, to do it. Especially if the
    upper piece has thermal flexure of its own, and is large.

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    Re: Bad solder joints on surface mount connector

    Can give a link to the connector data sheet? I don't understand the pin form and how it's touching the pad. Why we see a "huge" block of solder?

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    Re: Bad solder joints on surface mount connector

    Hairline fractures are visible in the solder under each pin.

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    Re: Bad solder joints on surface mount connector

    Thanks Dick, good idea about holding it in place.
    FvM, I don't have full datasheet sorry. It's a samtec ZHR5-20-02-F-RA though. Drawings available online. Incidentally, we had some problems with the plastic connector warping during reflow. Anyone had similar problem before? I wonder if that movement is causing cold joint?

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    Re: Bad solder joints on surface mount connector

    Thanks, I can see the pin form. My impression of an excessive gap between pin and pad is probably wrong. However, what's the actual gap after reflow? Did you make a microsection?

    Incidentally, we had some problems with the plastic connector warping during reflow. Anyone had similar problem before? I wonder if that movement is causing cold joint?
    I think, it can well explain it. Wrong temperature profile?

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    Re: Bad solder joints on surface mount connector

    I concur, the joints look overcooked and as stated previously some movement during the soldering process. I also think there is far to much solder on the joints, check the footprint and actual PCBs especially the locating holes for the connector. Also check that it is flat to the board pre-reflow.

    •   Alt12th April 2017, 10:18

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    Re: Bad solder joints on surface mount connector

    FvM, yeah microsection shows a small gap between pad and tail, maybe 0.1mm or so. On bad joints this is quite full of voids and some are full cracks.

    Marce, thanks. We are trying different stencils. .. can too much solder be a bad thing (assuming we don't get shorts?

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