•It is the first time to report the ZnO whiskers growth on the surface of SnZn/Cu.•Sn9Zn alloy shows a short circuiting failure risk for electronic interconnection.•The growth mechanism of ZnO whiskers was researched.In this work, we have found the formation of ZnO whiskers in SnZn/Cu solder joints interconnection in concentrator silicon solar cells solder layer. Different morphologies of ZnO whiskers were precipitated from rich-Zn phase. During oxidation, the diffusion of Zn atoms induces the formation of voids. The volume expansion (near surface zone) and volume shrinkage (inner zone) both appear in the microstructure matrix, and the tensile stress resulting from oxidation is the driving force for ZnO whisker growth. Net-type oxidation morphology along the triangular grain boundary resulting from that Zn diffuses onto the free surface along the grain boundaries of Sn was found synchronously.

•0.1 wt.% La2O3 nano-particles are selected as the additives into these solders for further improve the property.•The La2O3 nanoparticles can reduce the diffusion coefficient and activation energies of IMC layers.•It is found that the La2O3 nanoparticles can enhance the reliability of SnAgCu/Cu solder joints.SnAgCu alloys are promising as the lead-free solders for replacing traditional SnPb solders, 0.1 wt.% La2O3 nano-particles are selected as the additives into these solders for further improve the property. The interface reaction and the growth kinetics of intermetallic compounds (IMC) at SnAgCu/Cu and SnAgCu-nano La2O3/Cu interface were investigated during thermal cyclic loading. The growth rate of IMC in SnAgCu-nano La2O3/Cu is lower than that of SnAgCu/Cu, the La2O3 nanoparticles can reduce the diffusion coefficient and activation energies of IMC layers. And the finite element simulation demonstrates that von Mises stress concentrates at the Cu3Sn layer near Cu6Sn5 layer, the crack can be found in the stress concentrated area in the experiment, and SnAgCu-nano La2O3/Cu shows small length of crack comparing with SnAgCu/Cu, which demonstrates the La2O3 nanoparticles can enhance the reliability of SnAgCu/Cu solder joints.

Microstructures and fatigue life of SnAgCu and SnAgCu bearing nano-Al particles in QFP (Quad flat package) devices were investigated, respectively. Results show that the addition of nano-Al particles into SnAgCu solder can refine the microstructures of matrix microstructure. Moreover, the nano-Al particles present in the solder matrix, act as obstacles which can create a back stress, resisting the motion of dislocations. In QFP device, it is found that the addition of nano-Al particles can increase the fatigue life by 32% compared with the SnAgCu solder joints during thermal cycling loading.

Composite lead-free solders, containing micro and nano particles, have been widely studied. Due to grain boundary drag or Zener drag, these particles can refrain the solder microstructure from coarsening in services, especially for Cu6Sn5, Ag3Sn intermetallic compounds and the β-Sn phases. Due to dispersion hardening or dislocation drag, the mechanical properties of the composite solder alloys were enhanced significantly. Moreover, these particles can influence the rate of interfacial reactions, and some particles can transform into a layer of intermetallic compound. Wettability, creep resistance, and hardness properties were affected by these particles. A systematic review of the development of these lead-free composite solders is given here, which hopefully may find applications in microbumps to be used in the future 3D IC technology.

Anand constitutive model of SnAgCuFe solder joints was studied, and 9 parameters were determined based on tensile testing. And the model was incorporated in finite element code for analyzing the stress-strain response of SnAgCuFe solder joints in WLCSP30 device. The results indicate that the maximum stress concentrates on the top surface of corner solder joints, and the stress-strain of SnAgCuFe solder joints is lower than that of SnAgCu solder joints. Based on the fatigue life model, the addition of Fe can enhance the fatigue life of SnAgCu solder joints. Therefore, the SnAgCuFe solders can replace the traditional SnPb to be used in electronic packaging