Display Your Know How: Footprints

There is no simple answer to this question. B is going to be a better option for most requirements but the split shown will only give about 30% paste coverage. Using fewer larger tiles would increase the percentage.

Using too much paste risks the device "floating" on the pad which may cause solder balls and/or the remaining pins to be lifted away from their pads resulting in opens. Using too little paste may cause the joint starvation and reduce power and thermal transfer.

Don't trust data sheets for paste. In my experience they rarely match real-world requirements. Ask your manufacturer for guidelines and work with them for the best compromise.

Good points eDAve, thank you for your contributions to the discussion! 

We reviewed this paste footprint and agree that yes the total area of paste looks a bit lower than the 50 -60% target for Thermal pads. Therefore we have created the following option C based on this larger area target. Let us know if you would agree with this and any further experience or thoughts on this option:

Yes, that's a good split.

Rounding the corners isn't really necessary on relatively large apertures.

In reality, rounding corners these days is only necessary to increase an area ratio on small pads where the ratio is less than about 0.7. Square corners have much less effect on paste release than the smoothness of the stencil walls. This is often enhanced with use of nano coating.

Yes, that's a good split.

Rounding the corners isn't really necessary on relatively large apertures.

In reality, rounding corners these days is only necessary to increase an area ratio on small pads where the ratio is less than about 0.7. Square corners have much less effect on paste release than the smoothness of the stencil walls. This is often enhanced with use of nano coating.