Session: 08-02 Mini-Symposium for Professor Dasgupta II

Paper Number: 97488

97488 - Thermal Degradation of the Cu-Sn Imc System: Analysis and Simulations 

The Cu-Sn intermetallic compounds (IMCs) formed between the SAC solder alloy and the Cu substrate provide sufficient physical bonding for reliable interconnects. However, due to the inherent brittleness of Cu-Sn IMCs, solder joints subjected to high strain-rate loading tend to fracture along/near the IMC interface. The strength of IMC decreases at elevated temperatures, rendering solder joints more vulnerable to brittle failure. To identify the thermal degradation mechanism of the IMC system, specimens were aged at 125°C for up to 1000 hours. Failure analysis after high-speed ball tests revealed that the fracture location gradually shifted from the Cu₆Sn₅ layer and the Cu₆Sn₅/Cu₃Sn interface to the interior of the Cu₃Sn layer as the aging time increased. Combined with the microstructural evolution observed in the IMC layered structure, a Cu₃Sn-controlling mechanism is proposed to explain the thermal degradation of the Cu-Sn IMC system. A mesoscale grain-level finite element model was developed to study the fracture of the Cu-Sn IMC system, in which the stochastic geometry of the Cu₃Sn layer was constructed from Voronoi tessellation diagrams and the grain boundaries were simulated by a cohesive zone model. The effect of the microstructural characteristics of the Cu₃Sn layer on the fracture of the Cu-Sn IMC system was parametrically investigated. The simulation results validated the proposed Cu₃Sn-controlling thermal degradation mechanism.

Presenting Author: Qian Jiang The Hong Kong University of Science and Technology