Tensile-Fatigue Behavior of Sintered Copper Die-Attach Material

Abstract

The tensile-fatigue behavior of sintered-copper die-attach materials was investigated by focusing on sintering-pressure dependence. Specimens for fatigue tests were prepared by sintering copper oxide paste made from copper oxide particles with a mean diameter of 200 nm in hydrogen atmosphere under low (4 MPa) and high (13 MPa) pressures at 623 K for 15 min. The tensile-fatigue test was conducted using micro-load testing equipment in air at room temperature. The fatigue tests were conducted under pulsating load conditions. The fatigue strength of the high-pressure specimens was higher than that of the low-pressure specimens when comparing them within the nominal stress range $\Delta \sigma $ . The fracture at the narrow neck part and the dimpled fracture at the peripheral part of the voids were observed in both types of specimens from fractographic studies. The $\Delta \sigma $ was converted to the total strain range $\Delta \varepsilon _{t}$ by using finite element analysis (FEA). It was confirmed that the fatigue strength of the high-pressure specimens was higher than that of the low-pressure specimens even when comparing them within $\Delta \varepsilon _{t}$ . The strain distributions at the neck part and peripheral voids were calculated through FEA using a microporous structure model to clarify the cause of the fatigue lifetime difference between the low-pressure and high-pressure specimens. The calculated strain in the low-pressure specimens was locally concentrated at some of the narrow necks and could be linked to perpendicular cracks with a high strain level, whereas that in the high-pressure specimens was broadly distributed between the voids with a low strain level. This difference in strain distribution seemed to be the cause of the difference in the fatigue lifetime between the low-pressure and high-pressure specimens.