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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. [ABSTRACT FROM AUTHOR]

The effect of loading type on the fatigue lifetime of sintered-silver die attach was investigated. The fatigue lifetime was measured by fatigue testing with micro-load testing equipment. The fatigue tests were conducted under displacement control with (reversed loading (stress ratio ${R}= -1$), pulsating-tensile loading (${R} =0$), and pulsating-compression loading (${R} = -\infty $)) at room temperature. The strain of the fatigue test was estimated by strain-displacement relation obtained from previous tensile test using the strain gauge. Sintered-silver specimens were made from prebaked microscale silver paste and pressurized at 10 MPa for 10 minutes in air atmosphere at 573 K. The fatigue lifetime of reversed-loading case was 1000 cycles, that of pulsating-tensile-loading case was 4000 cycles, and the pulsating-compression-loading case remained unbroken. This suggests that compression load does not contribute to the destruction of the sintered silver. These measured fatigue lifetimes were aligned in a row when these are organized by maximum stress (tensile stress range). For fatigue lifetime evaluation of sintered silver, evaluation focusing on tensile stress seems to be important. [ABSTRACT FROM AUTHOR]

Macro- and micro-deformation properties of sintered copper die-attach material were evaluated. The macro-deformation properties are the properties, including the contribution of voids, and the micro-deformation properties are the properties, excluding the contribution of voids. Macro-deformation properties were evaluated by tensile tests at room temperature along with finite-element analysis (FEA). The specimens for these tests were made by sintering copper-oxide nano particles in the form of paste in a hydrogen atmosphere under low and high pressures. The micro-deformation properties were estimated by tensile test and FEA using a model that reproduces the micro-porous structure obtained from processing focused-ion beam scanning electron microscope data. The micro-stress/strain curve estimated for sintered copper was found to lie above the sintered silver and below the bulk copper. The porosity dependency of the macro-deformation properties of sintered copper was calculated using FEA models and the estimated micro-deformation property. The results obtained show that the macro-deformation properties of sintered copper are higher than those of sintered silver with similar porosity. This suggests that sintered copper die-attach material requires a lower sintering pressure than for sintered silver to achieve the same strength. [ABSTRACT FROM PUBLISHER]

Effects of pressurization and thermal-processing conditions on the deformation properties of sintered-silver sheets, excluding the contribution of the voids, (hereinafter, referred to as “micro-deformation properties”) were evaluated. Three types of thin-plate specimen sintered under the different conditions were prepared and these micro-deformation properties were compared. The first type was pressurized at 10 MPa for 10 min in the atmosphere at 573 K, the second type was annealed at 573 K for six hours before pressure processing and pressurized at 10 MPa for 10 min in the atmosphere at 573 K, and the third type was not pressurized and sintering in the atmosphere at 573 K for 10 min. The micro-deformation properties of these specimens were estimated by tensile testing and finite-element analysis (FEA) using a model that reproduces the microporous-structure. The microporous-structure models were made from serial cross-sectional images obtained by focused-ion-beam scanning electron microscope. These estimation results indicate that the micro-deformation properties of sintered-silver sheets do not depend on pressure, but on thermal-process conditions. The estimated micro-deformation properties were compared with those determined by nanoindentation tests and the validity of the estimated micro-deformation properties was confirmed. A deformation property of non-pressurized specimens was predicted by using the estimated micro-deformation properties and the microporous structures obtained from the pressurized specimens. The predicted deformation properties corresponded to experimental one. It is therefore concluded that if the deformation properties and microporous-structure of a sintered-silver specimen under a certain condition are determined, it is possible to predict the porosity dependency of deformation properties by FEA. [ABSTRACT FROM PUBLISHER]