Fig. 1. Cross-section observation of Cu sinter joints at the as-bonded state ((a) and (b), (b) is the enlarged micrograph of a), stored at 200 °C/ambient for 1000 h (c), and 200 °C/vacuum for 1000 h (d), (e) and (f) were the SE and the element overlay obtained by EPMA of Cu sinter joint stored at 200 °C/ambient for 1000 h.

Fig. 2. Shear strength of various Cu sinter joints before and after thermal storage of 200 °C/ambient for 100 h (a); the shear strength evolution of Cu sinter joints obtained at 300 °C during thermal storage test under ambient (black square) and vacuum (red circle) conditions (b).

Fig. 3. Fracture observation of Cu sinter joints at the as-bonded state (a), stored in 200 °C/ambient for 100 h (b) and 1000 h (c), and stored in 200 °C/vacuum for 1000 h (d). Fig. 3(e-h) is the enlarged micrographs for Fig. 3(a-d), respectively.

Fig. 4. EDS and XRD profiles of Cu sinter joints during the storage test. The EDS profiles were obtained from Cu joints after 1000 h in 200 °C/vacuum (a), after 100 h in 200 °C/ambient (b) and after 1000 h in 200 °C/ambient (c). The relationship between O content and storage time. (d) Copper oxides can be identified in XRD profiles (e).

Fig. 5. The schematic diagram of electrical measurement on Cu sinter joining (a), and the corresponding photographs (b), equivalent circuit diagram (c) and the electrical resistance evolution of the Cu sinter joints during the thermal storage (d).