Hi, all.
Is this acceptable practice to use an array of microvias in thermal pads to get down the ground plane?
Say construction is HDI type III (0.1mm microvias).
Through hole vias really muck up routing and placement on the opposite side of the PCB.
It starts to make things a bit messy because the component libraries become dependent on the layer stackup, but..
Tks,
--sp
Do blind vias need to be micro? The idea is to maximize the cross-sectional area, of course. I don't see why this wouldn't work.
I've gotten mixed signals on regular thermal vias in thermal pads. Basically, unfilled vias wick solder and the assembly people hate 'em. They like filled vias fine.
A blind micro-via array might or might not upset them, dunno. But the total wicking capacity is at least much less.
Cheers, James Arthur
How about outgasing from a blind via. Gas can only go through the upper side and might lift the component.
-- Reinhardt
If they're plated closed (as often happens on microvias, IIRC?), it shouldn't be a problem for anything; bonus, you should be able to place them at high density, perhaps even getting more Z-axis conductivity than a pattern of drilled and solder-filled vias.
Also, laser drilled vias are tapered, right? So you don't have to worry too much about trapped gas. Maybe a teeny bubble of solder flux in the remaining dimple (it's usually not a perfectly flat surface), but not a whole cylinder of gas and goo.
I've seen a lot of HDI boards without apparent vias, because they're doing via-in-pad and no caring. Seems good to me!
Tim
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