Screaming Circuits: Land Patterns - Equal and Not Equal


Land Patterns - Equal and Not Equal

I was recently asked a question about QFN package varieties. The questioner wanted to know if different package variants of 16 contact QFN packages, such as HUQFN, DHVQFN, SQFN and such, all shared the same footprint.

If they did, the CAD work would be much easier. There would be one land pattern to worry about and that would be that. Unfortunately, that is not that and in this case, that, in fact, that may never be that.

Many different varieties of QFN packages could use the same land pattern, but they don't always do. Some will have the same pitch, but more distance between the outside contacts and the corner, thus a greater overall dimension. That can happen even with the same labeled variety of QFN package. Some will have different dimensions, differnt pitch, different pad sizes or different thermal pad sizes. Sorry. No easy answer here.

I popped on over to the NXP website, one of our Circuit Design ECOsystem partners, for some examples. NXP lists two 60 contact HUQFN part packages. One is 5mm x 5mm. The other is 6mm x 4mm. Same with the HVQFN. There is a .65mm pitch 4mm x 4mm package and two.5mm pitch 3mm x 3mm parts with a different overall package outline.

In general, generalzations aren't going to work here. You're going to have to go dig out that datasheet and quite possibly create a new land pattern.

Duane Benson
One pattern to rule them all and in the solder bind them

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