Effect of Crystal Plane Spacing on Interface Stability of CoSn3(110)/Cu6Sn5(100) in IC Package

In micro-interconnect solder joints, the solder reacts with the substrate, and the growth of Intermetallic Compounds (IMCs) is prone to occur at the interface. In the production process, due to the addition of one or more alloying elements, the number of layers of intermetallic compounds will increase. There will be more and more complex interfaces in the formed multiphase IMC structure, the stability of the multilayer interface greatly affects the reliability of solder joints. To further explore the interface between various intermetallic compounds α-CoSn
3
and η'-Cu
6
Sn
5
. In this paper, the simulation of first-principle calculation is used to construct the heterojunction model, and the stability of CoSn
3
/Cu
6
Sn
5
interface is studied. The stability of CoSn
3
/Cu
6
Sn
5
interface was studied from atomic level of view. The results show that the surface energies of CoSn
3
and Cu
6
Sn
5
crystal planes begin to converge when the number of atomic layers exceeds 5 layers. The surface energy of the CoSn
3
(110) crystal plane converges to 0.98 J/m
²
, and the surface energy of the Cu
6
Sn
5
(100) crystal plane converges to 0.70 J/m
²
. The most stable structure can be obtained after adjusting the interfacial spacing. The calculation results show that the interfacial adhesion energy is 0.96 J/m
²
and the interfacial energy is 0.72 J/m
²
when CoSn
3
/Cu
6
Sn
5
interface is more stable in thermodynamics.