Electronic – Vias on QFN centre pad in Eagle PCB


I'm using some QFN devices in a PCB I'm designing using the Eagle PCB software. The QFN packages have a centre pad that is grounded and intended to help with thermal dissipation.

When creating the package, if I have the centre pad as an actual pad then I get DRC errors when I come to place vias on the pad to connect it through to the ground plane on the opposite side of the board.

Another possibility would be to leave the centre pad off the package and draw it in on the board, but this is a pretty unsatisfactory solution.

What's the best way of dealing with this problem?

Best Answer

Ok, I've found a solution to this problem.

The answer is to place the centre pad in the package with "stop" and "cream" turned off, then manually draw in rectangles for the "stop" and "cream" layers over the pad as they would've appeared anyway.

The physical end result is the same, but placing vias on the pad doesn't produce DRC errors.