Unacceptable voiding under a die
With less voiding under a power die, more heat can be dissipated through the solder into the substrate, heatsink, or lead-frame. Decreasing the amount of voids under a die is not only suggested for maximum solder joint strength, it is mandatory for sufficient thermal transfer. There are several tricks to reduce voiding, especially when using a solder paste. One of the most effective ways to lower voiding is though iterative profiling.
But what is acceptable voiding? Some die-attach processes limit voiding to 25% of the solder area under the die – although many people accept nothing more than 10%. With proper profiling and a good solder paste, voiding can be limited to <5% in almost any application.