Constitutive Relationships of Lead-Free Solders Materials

Objectives

Background

Approach

Objectives

(1) Determine constitutive relationships of a lead-free solder from isothermal mechanical tests.
(2) Provide guidelines for accelerated stress testing.

Background

Thermal and vibration loading cause cyclic deformations in electronic assemblies, resulting in fatigue damage in surface mount interconnects. Reliability of interconnects can be predicted by employing a stress model and a fatigue prediction (damage) model. The constitutive properties are one of the most critical parameters required for accurate stress analysis. In the case of solder, this includes elastic, plastic and creep properties at different strain rates and different temperatures. For the newly developed lead-free solder materials, the constitutive behavior is not known, which limits extension of the existing reliability prediction models for lead-free solder materials.

Approach

1. Design a specimen test configuration and fabricate specimens
2. Collect stress-strain curves at different strain rates and temperatures on a microtester setup
3. Collect creep curves at different stress levels and temperatures on a microtester setup.
4. Determine viscoplastic constitutive behavior.