Yoshihiko Kanda

Influence of Cyclic Strain-Hardening Exponent on Fatigue Ductility Exponent for a Sn-Ag-Cu Micro-Solder Joint

The fatigue ductility exponent in the Coffin–Manson law for a Sn-Ag-Cu micro-solder joint was investigated in terms of the cyclic strain-hardening property and the inelastic strain energy in fracture for isothermal fatigue. The fatigue ductility exponent was found to increase with temperature and holding time under strain at high temperature. This exponent is closely related to the cyclic strain-hardening exponent, which displays the opposite behavior in that it decreases with increasing temperature and with coarsening of intermetallic compound particles while holding under strain at high temperature. This result differs from the creep damage mechanism (grain boundary fracture), which is a primary reason for the significant reduction in fatigue life for all strain ranges for large-size specimens.

Effect of joint size on low-cycle fatigue properties of Sn-Ag-Cu solder joint

The influence of the joint size on low cycle fatigue characteristic of Sn-Ag-Cu has been investigated by a miniature joint specimen fabricated using micro solder balls. The influence of the size on crack initiation life is not remarkable, while the life which reaches complete failure reduces greatly when the ball size is decreased less than 150?m. The reduction in life is due to that the crack propagation stage does not appear and complete failure occurs simultaneously with the crack initiation in the ball size less than 150µm. The failure in the smallest size is induced by formation of subgrain boundary formation that occurs in whole area of the joint.

Thermal fatigue life evaluation of CSP joints by mechanical fatigue testing

The interrelation between a thermal cycle test and a mechanical shear fatigue test has been studied for CSP joints from the view point of fatigue life and the microstructural damage of solder joints. The fatigue lives in both methods are almost equivalent even though loading method is different. From the viewpoint of microstructure, the fact is attributed to that the transgranular failure is predominant mode and a microstructural coarsening which is induced by thermal loading and stress equivalent for both the thermal cycle test and the mechanical shear fatigue test.

Fatigue life and fracture behavior of micro size Sn-Ag-Cu solder joint

The influence of the joint size on low cycle fatigue characteristic of Sn-Ag-Cu has been investigated by a micro size joint specimen fabricated using solder balls. Although the effect of joint size on crack initiation life is not obvious at 298K, the reduction of the joint size changes the cyclic strain hardening nature and the fracture behavior that induces the life reduction at 398K. With a decrease in size, the failure mechanism transforms from a transgranular fracture to an intergranular fracture at the high energy grain boundary that is formed by high angle boundary formation following dynamic recovery in whole of joint. Therefore, the failure life is greatly reduced as a complete failure occurs simultaneously with the crack initiation at the grain boundaries. This is more remarkable at higher temperatures.Copyright

Effect of cyclic strain-hardening exponent on fatigue ductility exponent for Sn based alloy

The influence of cyclic strain-hardening exponents on fatigue ductility exponents for Sn-Bi solid solution alloys and Sn-Ag-Cu microsolder joints was investigated. In Sn-Bi solid solution alloys, the fatigue ductility exponent in Coffin-Manson’s law was confirmed to increase with a decrease in the cyclic strain-hardening exponent. On the other hand, in the Sn-Ag-Cu miniature solder joint, the fatigue ductility exponent increases with a rise in temperature and strain holding. Thus, the fatigue ductility exponents are closely related to the cyclic strain-hardening exponent: the former increases due to the depression of the latter with a rise in temperature and increase in intermetallic compound particle size during strain holding. The results differ for the creep damage mechanism (grain boundary fracture), which is the main reason for the life depression in large-size specimens.Copyright