**11.5 Kirkendall (IMC) voids**

Kirkendall voids arise in the intermetallic layer between the solder and the solder pad. They are created when joining two metals with different diffusion coefficients. These voids are most commonly located on the interface between a tin solder and

**Figure 20.** *Shrinkage voids.*

**Figure 21.** *Microvia void.*

a copper solder pad. Tin has a lower diffusion coefficient and thus penetrates more slowly into the copper than copper into tin.
