Study on laser and hot air reflow soldering of PBGA solder ball

Laser and hot air reflow soldering of PBGA solder ball was investigated. Experimental results showed that surface quality and shear strength of solder bump reflowed by laser was superior than the solder bump by hot air, and the microstructure within the solder bump reflowed by laser was much finer. Analysis on interfacial reaction showed that eutectic solder reacted with Au/Ni/Cu pad shortly after the solder was melted. Interface of solder bump reflowed by laser consists of a continuous AuSn 4 layer and remnant Au element. Needle like AuSn 4 grew sidewise from interface, and then spread out to the entire interface region. A thin layer of Ni 3Sn 4 intermetallic compound was found at the interface of solder bump reflowed by hot air, and AuSn 4 particles distributed within the whole solder bump randomly. The combination effect of the continuous AuSn 4 layer and finer eutectic microstructure contributes to the higher shear strength of solder bump reflowed by laser.

Effects of Zn addition on mechanical properties of eutectic Sn-58Bi solder during liquid-state aging

Interfacial reaction, tensile strength and creep resistance of Sn-58Bi-x Zn(x=0, 0.7, mass fraction, %) solder samples during liquid-state aging were investigated. The coarsening of Bi and the growth of Cu-Sn intermetallic compounds(IMCs) in Sn-58Bi-0.7Zn solder sample were both effectively suppressed. With the addition of 0.7% Zn, ultimate tensile strengths(UTSs) of the Sn-58 Bi solder slabs were respectively increased by 6.05% and 5.50% after reflow soldering and liquid-state aging, and those of the Cu/Sn-58Bi/Cu solder joints were also increased by 21.51% and 29.27%, respectively. The increase in strengthening effect of Cu/Sn-58Bi-x Zn/Cu solder joints could be attributed to the fracture surface which was changed from the Cu/IMC interface to the IMC/solder interface due to the finer Bi grain. Nanoindentation results revealed that the creep behavior of Sn-58Bi-0.7Zn solder was significantly improved compared with that of the eutectic Sn-58 Bi solder after reflow soldering and liquid-state aging.

ZnO whiskers growth on the surface of Sn9Zn/Cu solder joints in concentrator silicon solar cells solder layer

ZnO whiskers observation on the surface of SnZn/Cu solder joints in concentrator silicon solar cells solder layer is reported. In the experiment,SnZn/Cu samples are left in laboratory after reflow soldering for two years before an examination by SEM,then ZnO whiskers can be observed obviously,which grows out from the rich-Zn phase of the samples and causes electrical short circuit in the electronics appliances,which demonstrates that the SnZn solder shows a risk for the short circuiting failure of an electronic device. Moreover,the growth mechanism of ZnO whiskers is researched based on cracked oxide theory,which provides the reference support for SnZn solders application.