Solder interconnection specimen design and test control procedure for vaild constitutive modeling of solder alloys

Abstract

Commonly, constitutive models of solder alloys are derived from mechanical tests performed on either bulk solder specimens or on specially assembled BGA test coupons where the stresses are borne by solder ball interconnects. It has been widely recognized that models derived from bulk sample test data may not be reliable when predicting deformation behavior at the solder interconnect level due to the differences in the inherent microstructures at these different scales. This is particularly critical for lead-free SnAgCu solder alloys owing to their complex microstructures. There are two primary challenges associated with developing models from solder interconnect level test data: the experimental complexity associated with accurately resolving and controlling displacement at the scale of the interconnection, and the nonuniformity of stresses inherent in the solder interconnection geometry. In testing at interconnection level, published studies have used testing techniques that don't control deformation at the interconnect and have made uniformity of stress (and strain) approximations that are mostly invalid. Developing constitutive models from such data can produce erroneous results. In this study, we first demonstrate tests that control deformation at the interconnection level. We then show how heterogeneous stress distribution in solder interconnects can significantly affect the constitutive modeling of solder alloys and describe the conditions under which approximations may be made in the determination of accurate constitutive models. We validate our approach through experimental testing on Sn3.8Wwt%Ag0.7Wt%Cu solder joints and finite element analysis.

Constitutive Behavior of Sn3.8Ag0.7Cu and Sn1.0Ag0.5Cu Alloys at Creep and Low Strain Rate Regimes

“…In a related study [21], the authors showed that the correct specimen design and accurate displacement control during testing were critical to obtaining meaningful constitutive models. Following this study, which is discussed in more detail in Sections II-A-D, a solder interconnection of low aspect ratio was selected as a test specimen.…”

Constitutive behavior and Anand model of novel lead-free solder Sn-Zn-Bi-In-P

“…In the review of various papers in the literature, Anand model has been applied to describe the deformational behavior of Sn-Pb solders and, more recently, to describe the behavior of lead-free solders [20][21][22]. For example, Wilde et al [23] investigated the constitutive relation of 92.5Pb5Sn2.5Ag with Anand model.…”