TEMPERATURE AND RATE DEPENDENT PARTITIONED CONSTITUTIVE RELATIONSHIPS FOR 95.5PB2SN2.5AG SOLDER ALLOY

Abstract

One of the biggest challenges for power electronic devices is to be reliable in harsh environments. The operating temperatures in typical applications can go as high as 200ºC. The die attachment material of a power electronic device is one of the weak links in the system. The eutectic Sn-Pb solder alloy, which is the most commonly used permanent interconnect in electronics packaging cannot fulfill these service requirements, hence there is a need to find suitable replacements.

Durability characterization is essential in order to accurately predict the reliability of the solder alloy chosen for the die attach material under life cycle loads. A large number of models are available, which can be used to determine the life of die attach in small signal and power modules, however the shortfall of these models is the lack of test data for all but the most common (e.g. eutectic Sn-Pb solder) die attach materials. Hence, relevant constitutive properties must be measured, as they are essential for quantitative characterization of damage accumulated in the die attach, the knowledge of which is essential for accurate durability assessment.

The aim of this study is to determine the relevant constitutive properties for high temperature high lead 95.5Pb2Sn2.5Ag solder alloy (Indalloy 163) by implementing the direct local measurement technique. Temperature and loading rate dependent mechanical and constitutive properties of the afore mentioned solder alloy have been obtained by modeling the experimental data gathered by conducting monotonic, isothermal, constant strain rate tests at a range of temperatures and strain rates utilizing miniature single-lap shear specimens, with a partitioned form of the general constitutive equation.