Kai-Jheng Wang

In situ investigation of the interfacial reaction in Sn/Cu system by synchrotron radiation

In situ investigation of the interfacial reaction in the Sn/Cu thin film during aging, and reflow was carried out by synchrotron radiation with high intensity and high resolution of x-ray. With this technique, the phase transformation and evolution of the Sn/Cu thin film during heat treatment can be directly and continuously investigated. Moreover, the information for coefficient of thermal expansion in intermetallic compounds was also evaluated by this approach.

Morphological and microstructural evolution of Sn-patch in SnAgCu solder with Ni(V)/Cu under bump metallization

In flip chip technology, the Ni(V)/Cu multi-metallic thin-films is a widely used under bump metallization (UBM), for doping 7 wt.% V into the Ni target can eliminate the magnetism of Ni during sputtering [1,2]. It was noted that V in the Ni(V) layer did not react with solders and intermetallic compounds (IMC) during reflow and aging process, yet a Sn-rich phase, as the so-called “Sn-patch”, would form in the Ni(V) layer [3]. The possible reason of Sn-patch formation may be the fast Sn diffusion from the solder matrix to the Ni(V) layer. However, the formation mechanism of Sn-patch and the detailed composition variation and structure evolution in Sn-patch were not fully discussed yet. In this study, Sn-patch would be analyzed by a field emission electron probe X-ray microanalyzer (FE-EPMA) and a transmission electron microscope (TEM) to elucidate the composition redistribution and the microstructure evolution, respectively. There existed concentration redistribution of the constituent element in Sn-patch, and its microstructure also varied with the aging time. On the basic of the detailed characterization by FE-EPMA and TEM, it was revealed that Sn-patch was consisted of crystalline Ni and amorphous Sn-rich phase after reflow, while V2Sn3 formed with amorphous Sn-rich phase during aging. A possible formation mechanism of Sn-patch was proposed, which could be employed to explain the corresponding composition variation and structure evolution associated with the Sn-patch formation.