Akio Furusawa

Formation of particle of bismuth–indium alloys and particle diameter by ultrasonic cavitation

The miniaturization of electronic equipment requires fine bonding. Therefore, it is necessary to miniaturize the solder particles used for bonding different materials. Ultrasonic cavitation is a technique that uses ultrasonic irradiation to synthesize such microparticles. In this study, we investigated the effects of ultrasonic irradiation conditions on synthetic microparticles produced by this technique. Spherical particles were obtained by irradiating Bi-45 wt% In melted in a solvent with ultrasonic waves for 15 s, and the resultant metal composition was found to be equivalent to the raw material composition. We found a clear correlation between the ultrasonic irradiation time and particle size. When irradiated for 60 min, the average particle diameter was 3.3 μm. In addition, the particle division rate decreased as the irradiation time increased, which is probably due to attenuation of the vibration wave as the boundary surface increased with the refinement of the particle.

Soldering Properties and Interfacial Microstructure of CSP Solder Joints with Lower Melting Lead-free Solder

In this paper we investigate the appropriate reflow profiles for simulated CSP solder joints using Sn-Ag-Bi-In solder, which has a lower melting point than Sn-Ag-Cu solder. We have examined the relationship between the interfacial microstructure and mechanical characteristics of Sn-Ag-Bi-In solder at the solder joints compared with those of Sn-Zn-Bi solder. When soldering Sn-3Ag-0.5Cu CSP balls on a Cu/Ni/Au pad, Sn-8Zn-3Bi showed high joint strength at 503 K or higher, whereas Sn-3.5Ag-0.5Bi-8In showed strength at the lower temperature of 493 K. This implies that Sn-Ag-Bi-In solder is more appropriate for soldering at lower temperatures. On the joint interface, a stratified Ni-Sn layer was formed when the Sn-3Ag-0.5Cu CSP ball was soldered on the Cu/Ni/Au phases are pad using Sn-3.5Ag-0.5Bi-8In at 483 ~ 493 K. At 503 K or higher, clumped (Cu,Ni)6Sn5 unevenly formed on the joint interface, resulting in lower strength. These results suggest the appropriate reflow thermal profile for Sn-3.5Ag-0.5Bi-8In sold...

Effects of Interfacial Microstructure on Strength of Solder Joint Using Sn-Ag-Bi-In Solder

In the present research a BGA (Ball Grid Array) type Sn-3Ag-0.5Cu solder ball was reflowed on Cu/Ni/Au pad using a Sn-3.5Ag-0.5Bi-8In solder or a Sn-8Zn-3Bi solder with varying reflow peak temperature and the interfacial microstructure and joint strength were evaluated. The strength of the Sn-3.5Ag-0.5Bi-8In solder joints reached the maximum value at reflow peak temperature of 483K to 493K and then decreased with increasing reflow temperature, whereas the Sn-8Zn-3Bi solder joints had high strength at the higher reflow peak temperature of 503K. In the Sn-3.5Ag-0.5Bi-8In solder joints, at a reflow peak temperature of 493K or less, a thin Ni-Sn type intermetallic layer formed at the interface between the solder and the pad. However at the higher reflow peak temperatures a clumpy (Cu, Ni)6 Sn5 phase locally formed on the Ni-Sn interfacial reaction layer. This is caused by Cu from melted Sn-Ag-Cu ball reacting to Ni and Sn in the interfacial region. The (Cu, Ni)6 Sn5 clumps increased with reflow peak temperature. Some void-like defects existed at the interface between the Ni-Sn layer and (Cu, Ni)6 Sn5 clumps. These defects can act as crack initiation sites and thereby cause the degradation of the joint strength. It is concluded from the results that when the Sn-3.5Ag-0.5Bi-8In solder is applied to reflow soldering of the packages having Sn-Ag-Cu solder bump on the Cu/Ni/Au pad, the reflow peak temperature should be controlled ranging from 483K to 493K. When the reflow peak temperature was over 493K, a holding of 20s at the peak temperature, which resulted in diminish the void-like defects at the interface between the Ni-Sn layer and the (Cu, Ni)6 Sn5 clumps, improved the joint strength.Copyright