Thermal stress analysis of a flip-chip parallel VCSEL (vertical-cavity surface-emitting laser) package with low-temperature lead-free (48Sn-52In) solder joints

Solders such as the 48wt%Sn-52wt%In, 42wt%Sn-58wt%Bi, 63wt%Sn-37wt%Pb, Sn(3-4)wt%Ag(0.5-0.7)wt%Cu, and 80wt%Au-20wt%Sn, are studied as interconnect materials in a vertical-cavity surface-emitting laser (VCSEL). The Sn52In alloy is a low temperature (melting point = 118degC) lead-free solder and a potential candidate material for this device. In this study, thermal-structural analysis evaluates the solder alloys in the context of in-service operating conditions. Specifically, the thermal analysis determines the in-service temperature distributions, as influenced by each solder alloy, due to power generation within the VCSEL and due to convective boundary conditions. Subsequently, these thermal profiles are used as the thermal loads in an evaluation of the stress and creep response in the laser pads and solder joints. Emphasis is placed on the relaxation of stresses at the laser pads and on the creep strains developed at the solder joints during a 24 hour power-on condition