Models for Lead-Free Solder Alloy

Constitutive Models for Lead-Free Solder Alloy 

The material constitutive model plays an important role in the development of thermomechanical models for microelectronic packaging assembly. Under thermomechanical loading, solder alloy undergoes elastic and inelastic de- 

The development of thermomechanical models typically involves (a) the development of constitutive models for the solder alloy and other materials in the packaging assembly, (b) the development of geometry models to represent the solder interconnects and the packaging assembly, and (c) the development of failure predictive models for the various material systems in the assembly. The thermomechanical models, when subjected to thermal excursions seen dixring accelerated qualifications or during field-use, will identify the location of failure, mode of failixre, and time to failure in various parts of the packaging assembly. Prior to usage, the models should be validated with experimental test data. 

Isotropic elastic properties, E, the Young s modulus, and t , the Poisson s ratio can be used to represent the elastic behavior of the solder alloy. The temperature-dependent elastic behavior of two lead-free solder alloys Sn-Ag-Cu and Sn-Ag are presented in this section. For example, E is given by  

The permanent deformation after the removal of the applied load is called the inelastic deformation and is divided into an instantaneous plastic deformation component and a time-dependent creep deformation component. 

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