Paste Containing 1.5 Μm 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 μm 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 oC resulted in a low shear strength of 8.15 MPa in the formed bondline. Although the annealing at 250 oC increased its strength, it did not reach 20 MPa, which is required for practical applications. Interestingly, the 10 s bonding at 300 oC exhibited sufficient shear strength of 21.96 MPa, and when annealed for 30 min at 300 oC, 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.