What’s Acceptable?

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 lower voiding, especially when using a solder paste. One of the most pronounced 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.