I'm using a DAC with an exposed pad (NC) bottom. The datasheet specifies that the EP should be connected to ground ([EDIT]Presumably [/EDIT] for heat dissipation, but heat concern is not noted in the data sheet ) but is not connecting internally in the IC, and since the DAC is my only mixed signal component it is my star ground point as well, I'm connecting it to the analog ground plane in the board.
My question is about the best practice when it comes to exposed pad connections. Specifically when it comes to attaching the IC ground and the power supply decoupling is it ok to connect the ground pin and decoupling cap through the Exposed pad to ground or is it better to have individual vias for the decoupling and ground connection?
To Illustrate:
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Best Answer
It really depends on how many layers your board will have.
If you have more than two layers, it will almost always be better to drop vias down to the ground plane and then have decoupling caps right underneath the ic on the opposite side of the board
If you are just doing two layers, then it is best to connect the EP, assuming there is only one ground (not separated analog and digital grounds), to the GND pins as well as place decoupling as close as possible to those pins. I wouldn't recommend routing the GND out any other ways (out a corner of the package) just because this can get pretty hairy and is not the most ideal in regards to parasitics.
If you do have separate grounds, make sure to connect yours to a signal ground, and NOT power ground. Power ground is very very noisy.