Underness as a Common Theme Again

I didn’t mean to, but here I seem to be with a common theme again. Like yesterday, and again not too long before that — parts under parts seems to be the thing of the hour.

Maybe the caps are shy and are just trying to hide. Or maybe we’ve been writing too much about package-on-package lately. Dunno.

I do wonder though, how many of these issues are caused by parts substitution (the cap originally chosen was narrower), the wrong CAD library footprint, or just a rushed layout. Who wants to vote on that one?

Duane Benson
Just push on it harder. We’ll make it fit.


Sometimes, it’s the simple things in life that we must stop and appreciate. Like the fact that just because there aren’t any pads in a spot, doesn’t mean that you can use the space.

Take this PCB, for example. U3 is placed so that one and a half of its legs will be underneath a big RF module. The module isn’t shown in the picture, but the pads and outline are shown. U3 is right into the lower left corner of the module as you can see by the rows of pads and the silk outline. The module that U3 steps under is one of those module on PCB using castellated mounting holes.

If U3 were your hot little sports car and the big module were a dump truck, you most certainly wouldn’t do this. You’d look first. That’s what mirrors are for.

C6 up on top is pretty darn too-close to the module too. Move it a few mils to the right please.

Duane Benson
Mirror mirror on the wall
Who is the overlappingest of them all