Screaming Circuits: QFN solder voids


QFN solder voids

I've written a couple of posts about QFN float problems (here), (here) and (here). There is another problem we run across as well.

With larger QFN parts, the opposite problem can occur in the center pad area. When the square opening for the solder paste stencil is fully open on a larger part – say 10 x 10 mm or larger – the paste squeegee may deform and actually scoop too much of the paste out of the opening. This canQfn_center_void_1  lead to uneven paste and solder voids. Both are potential reliability problems.

The solution is the same. Segment the stencil opening to create an even paste distribution.

Duane Benson
Squeegees aren't just for window cleaning

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