Lead free solder materials are widely used as interconnects in electronic assemblies due to relatively better mechanical properties, high melting temperature, environment friendly chemical properties, and thermal cycling reliability. These properties of lead-free electronic assemblies largely depend on their operating temperature. Electronic devices are often subjected to different thermal cyclic loading during their service life in various applications such as aerospace engines, automotive power electronics, well drilling, and geothermal energy. Therefore, the evolution of mechanical properties of lead-free solder materials subjected to different thermal cycling profiles need to be investigated.

 

In our previous work, mechanical behavior evolution of SAC305 lead free solder material was investigated under different thermal cyclic loadings for up to 5 days of cycling. In the present work, we have extended our previous study for up to 100 days of cycling.  The SAC305 materials are chemically composed of 96.5% Sn, 3% Ag, and 0.5% Cu. The specimens for uniaxial tensile testing were prepared using vacuum suction method, water quenched solidification, and finally reflowing with a controlled temperature profile in rectangular cross-section glass tubes. Afterwards, the prepared samples were placed into the thermal cycling chamber and cycled under a stress-free condition (no load) from -40 C to +125 C.  Several thermal cycling profiles were investigated: (1) 150  minutes cycles with 45 minutes ramps and 30 minutes dwells, (2) air-to-air thermal shock exposures with 30 minutes dwells and near instantaneous ramps, (3) 90 minute cycles with 45 minutes ramps and 0 minutes dwells (thermal ramp only), and (4) Isothermal aging at high temperature extreme (no cycle). Stress-strain tests were performed on the uniaxial test specimens to investigate the change in mechanical properties which includes effective elastic modulus (E) and ultimate tensile strength (UTS) after the exposure under different thermal cycling profiles. The test results were compared with each other in order to understand the effect of different thermal cycling profiles on the mechanical properties of SAC305 solder materials.


Evolution of Mechanical Properties of Sac305 Lead Free Solder Materials Subjected to Different Thermal Cycling Profiles

Division / Sponsors: 
Electronic & Photonic Packaging Division (EPPD)

Paper Proceedings: https://asmedigitalcollection.asme.org/InterPACK/InterPACK2020/volume/84041

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