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MAT7E – Influence of Microalloying Elements on Reliability of SnAgCu Solder Joints
Author: Babak Arfaei
Abstract: New solder alloys (SAC with microalloying elements such as Ni, Mn and Ti, Sb or Bi) are under evaluation as potential replacements for SAC305 lead free solder. Researchers seek a lead free solder alloy with greater resistance to drop shock that also demonstrates acceptable thermal fatigue resistance. The effects of various microalloying additions to SAC alloys on the evolution of solder joint microstructure and on failure mechanisms must be understood in order to optimize the implementation of these new materials.Thus various commercial solders alloys with microalloying elements, such as SN100C, SACM and Innolot, were examined and compared to observations for SAC105, SAC 305 and eutectic SnPb alloys. Both mechanical and thermal cycling tests were performed on solder joints assembled on Cu-OSP or ENIG. The thermal history of each individual solder joint was carefully controlled and monitored by differential scanning calorimeter. Thus the effects of varying reflow parameters on the mechanical behavior in shear and shear fatigue test were analyzed. ATC reliability test was conducted on BGA components using a -40/125°C profile.Careful microstructural analysis was performed on as reflowed and failed samples. Polarized light microscopy and electron backscatter diffraction techniques were used to assess the effect of Sn grain morphology on life time of solder joints, particularly on early and late failures. The effect of variation in solder volume, composition, Sn grain morphology and PCB surface finish on solder joint microstructure and lifetime was carefully evaluated.