Screaming Circuits: Novel QFN Land Pattern


Novel QFN Land Pattern

Novel QFN groundingBecause the center land is so much bigger then the side pads, QFN solder paste can be a problem if not handled properly. I've written about options before, but here's another approach. I ran across this QFN land pattern the other day.

This one's a bit easier to start with because either there aren't any vias needed or they and filled and plated over. It also looks like there isn't much of a thermal issue here. In some cases the center pad is needed for heat sinking, but in other it's just there as a ground. My guess is the latter is the case here.

By creating a bunch of openings that are the same size as the side contacts, this QFN will get good grounding and there won't be any issues with too much or too little solder paste getting in the way. It pretty much bypasses the standard QFN problem.

Note that the designer must have the same pattern in the solder mask layer as in the paste layer. If only the paste layer was like this, the solder would spread out and there would likely be too much voiding. It might not connect in the center at all. If only the mask layer was like this and the paste layer was fully open, there would be so much solder with nothing to stick too. It would just be a big mess. Yuck ☠.

Duane Benson
QFN Tetris anyone?


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