Feasibility investigation and characterization of low-pressure-assisted sintered-silver bonded large-area DBA plates

Abstract

Purpose This paper aims to use nano-silver paste to design a new bonding method for super-large-area direct-bonded-aluminum (DBA) plates. It compared several frequently used bonding methods and proved the feasibility of an optimized low-pressure-assisted double-layer-printed silver sintering technology for large-area bonding to increase the thermal conductivity of power electronic modules with high junction temperature, higher power density and higher reliability. Design/methodology/approach The bonding profile was optimized by using transparent glasses as substrates. Thus, the bonding qualities could be directly characterized by optical observation. After sintering, the bonded DBA samples were characterized by nondestructive X-ray computed tomography system, scanning electron microscopy equipped with an energy dispersive spectrometer. Finally, bonding stress evolution was characterized by shear tests. Findings Low-pressure-assisted large-area double-layer-printed bonding process consisting of six-step was successfully developed to bond DBA substrates with the size of 50.8 × 25.4 mm. The thickness of the sintered-silver bond-line was between 33  and 74 µm with the average porosity of 12.5 per cent. The distribution of shear strength along the length of DBA/DBA bonded sample was from 9.7  to 18.8 MPa, with average shear strength of 15.5 MPa. The typical fracture primarily propagated in the sintered-silver layer and partially along the Ni layer. Research limitations/implications The bonding stress needs to be further improved. Meanwhile, the thermal and electrical properties are encouraged to test further. Practical implications If nano-silver paste can be used as thermal interfacial material for super-large-area bonding, the thermal performance will be improved. Social implications The paper accelerated the use of nano-silver paste for super-large-area DBA bonding. Originality/value The proposed bonding method greatly decreased the bonding pressure.