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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Lumpy joints


Lumpy joints | 14 December, 2001

This is one I haven't seen before (not in this context, anyway).

We have an assembly that we have the SMT done out of house on, because of the high volumes. The boards have two distinct characteristics with respect to the appearance of the solder joints. One population has a lumpy but shiny appearance, good wetting angles, with smooth nc flux residue . The other population has nice shiny joints that are covered with a hard residue (nc flux) that has concentric cracks in it, starting about 1/2 way down the fillet. I'm not concerned with the latter, but the former gives me the creeps. They simply look like some of the metal didn't quite reflow completely, whether because of insufficient heat, lousy flux activity (maybe old paste, too much down time, something like that).

I figure they're running these boards on two lines, one with a problem, one without. Probably neither have any real process control. Since they're in China I can't really verify it myself.

Some of them look like they might be showing some dewetting, although very little, and since dewetting is something I haven't experienced here I can't be sure.

Anyway, it seems odd that incomplete reflow would be occurring where we also see good wetting angles, but maybe that's just my lack of worldliness talking.

Whattya think.....rotten paste, bad profile, what? I know I don't wanna use them, but I may have to let the managers decide. Oh, the horror........

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Lumpy joints | 15 December, 2001

Lumpy doesn't sound good.

Why not section some of these connections to convince your vaulted leaders that this is not the product they should be shipping to your customers?

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Lumpy joints | 17 December, 2001

Well, I was able to convince them we had a serious problem on the poorly reflowed boards without spending 2k on off- site analysis.

Now all we have to do is sort out the ones that flowed well but had solder balls (looks like a damaged stencil problem) on them from the ones without solder balls. Maybe I should try and come up with a ball park figure for how much money we actually "saved" (chortle, guffaw) by going over seas for this stuff.

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Reflow Oven

Metcal soldering rework