When using a diffusion barrier underneath the solder
pad it is possible to perform even two solder reflow
processes. The first component is attached to the first
solder pad. The subsequent soldering process leads in this
interconnection to dissolution of gold from this
component in the solder and to the formation of z-phase.
Thus, this joint will withstand at a second reflow process.
During the latter, a second component can be soldered.
This way, it is possible to create at least a two step solder
hierarchy with only one solder alloy.