Thermo-mechanical reliability of lead-free solder interconnects

Abstract

Lead-free solder for electronic assemblies and systems is fast becoming a reality primarily because of market driven forces. While the industry has identified possible alternatives to SnPb solder, much work still needs to be done, especially in the following areas: solder materials characterization (temperature and stress dependent inelastic behavior creep and stress relaxation, bulk versus joint behavior), failure mechanisms related to the solder joints of the new alloys (will creep deformation still play a dominant role for e.g. thermally induced low cycle fatigue?), temperature cycle data, for instance, on real components (acceleration factors may depend on accelerated test conditions and solder alloys, and field conditions may be much more benign than accelerated test conditions), life prediction models (models have to incorporate time and temperature dependent behavior of solders, implementation of constitutive equation in FEA software is one of the keys, isothermal fatigue data should not be useful for life prediction model development), solder-surface interactions (solder reacts with metallization to form interfacial intermetallics, intermetallics grow with time and temperature, metallization consumption by intermetallic growth, intermetallics within the solder, thermo-mechanical properties of the intermetallics), and assembly process development. The impact of some of these issues on the reliability assessment of lead-free solder interconnects through experiments and FE calculations is discussed in the paper, shown on examples like SMD-components and Flip-Chips

Primary Creep in Sn3.8Ag0.7Cu Solder. Part I: Theory, Experiments, and Data Reduction

“…It has also been considered to be solely a function of minimum strain rate for Sn4.0Ag0.5Cu. 25 In both cases the strain hardening was assumed not to be thermally activated. In contrast to these two assumptions, Fig.…”

Effect of Bi on the microstructure and tensile behavior of Sn‐3.7Ag solders

“…When the 4 wt% of Bi was added to the solder, macroscopic defects, such as cracks and pores, were induced by fast cooling of water quenching (Figure 5). Moreover, because of the difference of coefficients of thermal expansion between the precipitated Bi particles, which is anisotropic from 11 to 17 ppm/°C depending on axis (Cave and Holroyd, 1960), and the Sn‐Ag solders, which is more than 21 ppm/°C (Schubert et al , 2001; Wiese et al , 2001), the generation of the defects might be promoted. The defects in the solder matrix are responsible for the low‐tensile strength of the fast cooled Sn‐3.7Ag‐4Bi solder.…”

Lifetime Evaluation of Nanoscale Silver Sintered Power Modules for Automotive Application Based on Experiments and Finite-Element Modeling

“…Therefore, the following evolution law of the SED f in the silver layer can be obtained for N f ageing cycles (2). Finally, after 6000 cycles (SED 6000 ), 6.182×10 9 J.m -3 SED is accumulated in the 3D-model (3).…”