I wrote recently about segmenting your solder paste stencils for the big open areas on your QFNs. The idea is that if the entire area is left open, it may end up with too much solder in the heat slug area, causing the part to lift up and not solder properly.

QFN center void CadstarGuy commented: “Also — when you have the full aperture in the stencil it can tend to drag as it is pasted leaving big gaps in the solder (and excess solder on the screen).”

That’s a very important point to remember. Ironically, leaving the area fully open can lead to either too much solder or not enough solder. Weird. Huh? The solution is the same: segment your stencil layer inside that center pad area.

Duane Benson
Anoid the void!