Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Dietrich Habel

#11586

Experience with solder stop on components? | 4 May, 1999

Does someone has experience with solder stop on components to avoid an Viking effect (no solder on the pad, all solder on the lead)? What kind of solder stop does work well? What is dangerous? What has to be kept in mind when using such components? Background: We are thinking about a solder stop for a connector.

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#11587

Re: Experience with solder stop on components? | 4 May, 1999

| Does someone has experience with solder stop on components to avoid an Viking effect (no solder on the pad, all solder on the lead)? What kind of solder stop does work well? What is dangerous? What has to be kept in mind when using such components? | Background: We are thinking about a solder stop for a connector. | Dietrich: Two things:

1 I'm not sure I should be asking this, but how does "no solder on the pad, all solder on the lead" relate to the "Viking effect?" 2 More to the point, I don't think that using solder stop is a satisfactory solution to your "no solder on the pad, all solder on the lead" problem. Rather, than put additional labor into a job by slopping solder stop on component leads and then having to remove it, and finding that it doesn't work anyhow; I would rather that you: 2a Ask "what is going on here, when a component lead solders well, yet the nearby substrate solders poorly?" 2b Determine the cause of that problem. 2c Fix the problem.

To get you started, broadly, soldering requires: proper heating, wetting of surfaces, contact with the solder, adequate solder, and immobile parts during solidification. I�m not sure of your process, but you might consider:

1 There is probably adequate heat available, but that portion of the substrate that�s not soldering well is not receiving proper heating. Why is the component getting so hot, relative to the substrate, that the component is taking all available solder? What is it about the substrate that is preventing it from heating properly? Where is the heat going? Are other components, vias, or substrate design of large copper plains draining-off the heat? 2 Some surfaces must be wetting, there is solder on the lead, so there must be flux. It is not likely the flux is burning off the pad, but not the component lead. What is it about this pad that it doesn�t wet? Do other pads on this substrate have good solder flow? What�s different about this pad? Is there a solder stop on it? Are both sides of the pad wetting poorly? 3 The component lead is contacting the solder, but is the substrate? I assume the majority of the substrate is contacting the solder, but is the dwell long enough to get good barrel flow? 4 Have to assume there is adequate solder available, since you�re talking about using solder stop to prevent it from wicking-up the component lead. 5 Have to assume parts are being held immobile during solidification.

Good luck

Dave F

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