In the electronics assembly arena, lead is being targeted due to the concern regarding environmental pollutants.  Thus, the lead-free solder and its reliability are getting highlighted.  During qualification testing, lead-free solders in electronic assemblies are typically subjected to thermal cycling.  In the lead-free solder material, microstructural evolution and material property degradation occurs due the thermal aging phenomena during dwell periods at the high temperature extreme of thermal cycling.  In addition, during ramping between low and high temperature extreme, lead-free solders can also experience aging phenomena.  In our prior work, we have compared material properties (stiffness and strength) degradation of lead-free solder materials in isothermal aging and five different thermal cycling exposures.  Changes in material properties were higher for all the thermal cycling exposures compared to the aging.  But microstructural evolution and material property degradation exacerbated as the ramp rate decreases in thermal cycling.

In this current study, the creep behavior evolutions occurring in SAC305 lead free solder subjected to thermal cycling exposures have been investigated.  Uniaxial test specimens were prepared by reflowing solder in rectangular cross-section glass tubes with a controlled temperature profile.  The samples were thermally cycled from -40 C to +125 C under a stress-free condition (no load) in an environmental chamber after reflow solidification.  The thermal cycling profile consisted of a 150 minutes cycle with 45 minutes ramps and 30 minutes dwells.  It was chosen for this study as in our previous study it showed most detrimental effects on mechanical behavior evolution.  In this condition, 10-15 samples were cycled for various durations of cycling (e.g.  48, 96, and 240 cycles), which were equivalent to various aging times at the high temperature extreme of T = 125 C.

After cycling, creep testing was performed on all the cycled samples at three different stress levels (10, 12 ,15 MPa) for 0, 1, 2, and 5 days of equivalent aging time.  All the tests were performed at room temperature.   For the specified thermal cycling profile, the evolution of the creep rate was obtained as a function of the stress level, as well as the net aging time at the high temperature extreme.  Results showed that the creep rate increases with the increase in stress level for 0, 1, 2, and 5 days of aging at high temperature extreme.


Thermal Cycling Induced Evolution of the Creep Behavior of Lead Free Solder Materials

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

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

InterPACK2020 - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.