A case study of intermetallic evolutions in a solder joint under electromigration using a novel experiment-simulation combined approach

In this work, by using high-resolution X-ray computed tomography (μ-XCT), we revealed the 3D Cu
6
Sn
5
evolutions in a typical single-crystal solder joint during electromigration (EM), and the finite element modeling (FEM) based on a reconstructed real solder joint model was performed to understand the microstructure evolution mechanism. Simulation results show that the migration direction of Cu atoms is nearly parallel with the c-axis of βSn. Primary Cu
6
Sn
5
rods within the region of higher Cu diffusion flux exhibit more obvious growth with higher volume change. Compared with the grown primary Cu
6
Sn
5
, the most ungrown Cu
6
Sn
5
rods demonstrate higher angles θ
c
between [001]
βSn
and [0001]
Cu6Sn5
(>38°). The abnormally less growth of low-θ
c
Cu
6
Sn
5
can be attributed to the chaotic Cu diffusion flux in the neighboring region that is the result of the complex geometry of the solder joint. The formations of new Cu
6
Sn
5
rods within the solder joint are influenced by the Cu
6
Sn
5
-βSn orientation relationship, with small angles (<20°) between [0001]
Cu6Sn5
with ${\langle 11\bar 2\rangle _{\beta {\text{Sn}}}}$. The formation of Cu
6
Sn
5
particles at the specific area of the anode interface is consistent with the local higher Cu concentration, as indicated by the simulation results.