Paste Containing 1.5? m Ag Particles with Enhanced Surface Area: Ultrafast Thermo-Compression Sinter-Bonding and Annealing Effects

To rapidly sinter a bondline and obtain mechanical stability at high temperature and high thermal conductivity, 1.5 mu m Ag particles with enhanced surface area were synthesized by a wet-chemical method, and a sinter-bonding paste containing these Ag particles was obtained. Some particles were present in the form of agglomerates of spike stems and short-branch dendrites, while others existed as spheres with rough nodule surfaces or relatively smooth surfaces. To determine an effective sinter-bonding process, a significantly short thermo-compression bonding (10 s) under 5 MPa in air and subsequent annealing in nitrogen were performed. The thermo-compression bonding at 250 degrees C resulted in a low shear strength of 8.15 MPa in the formed bondline. Although the annealing at 250 degrees C increased its strength, it did not reach 20 MPa, which is required for practical applications. Interestingly, the 10 s bonding at 300 degrees C exhibited sufficient shear strength of 21.96 MPa, and when annealed for 30 min at 300 degrees C, the excellent strength of 37.75 MPa was obtained. The bondline porosity of 12.16% immediately after the thermo-compression bonding, decreased to 9.13% after annealing for 30 min. The densification in bondline by the annealing also induced a change in the fracture path as well as enhancement in the shear strength. Thus, the suggested subsequent annealing is an effective method for sinter-bonding, similar to the pressureless sinter-bonding process. Consequently, the synthesized Ag particles exhibited superior sintering properties and the suggested combination process shows potential for tremendously improving chip sinter-bonding productivity.