Quote from: 2112 on December 31, 2012, 05:58:31 PM

Quote from: MrTeal on December 31, 2012, 05:48:55 PM

Diablo, the small adhesive attached BGA heatsinks weigh almost nothing. They're not going to stress the chips.

But are they going to help? BGA cases are flip-chip; with chip substrate connected to the top of the case.

QFN packages don't flip the chip and actually have air between the top of the package and the chip, because they need to accommodate the bonding wires. They really want to be cooled through the bottom of the PCB because this is where they have the least thermal resistance and a biggest piece of metal: ground connection for the substrate.

They do, but I think you'll be fighting a difficult battle cooling them through the thermal pad depending on the board design. Given the massive number of chips, the density is probably going to be quite high to keep board size reasonable. Cooling through the ground plane only works well if there aren't 8 chips all around the one is question all dumping heat in as well. If they can manage to keep the bottom clean they could definitely use a back plate to help cool the board.

Most QFNs have epoxy from the top of the die to the top of the package. It might not be a great thermal interface, but given the very low power per chip it will still be able to help.