LOW STRESS SILVER GLASS DIE ATTACH MATERIAL

The sintering characteristics of a silver filled lead borate glass composite has been studied since it influences die stresses. This is especially true for very large area die attachments. The kinetics of silver particle sintering in the presence of liquid phase glass is examined by dilatometry and by electron microscopy. During heat treatment, the sintering rate is significantly increased after the glass becomes liquid. This can cause excessive die stresses, resulting in cracks, typically at the die-bond interface, and/or poor adhesion. The sintering process is influenced both by material parameters such as silver flake surface area, glass transition temperature, additives, and by process profiles such as temperature ramp rate and dwell time. It was found that by adding a small amount of appropriate additives, one can either increase or decrease the sintering rate significantly. Thus stress relief in large area dice can be achieved by using additives in silver-glass to control the sintering rate. In addition, the dispensing characteristics are determined by the Theological properties of the paste. We have identified the key rheological parameters that influence various dispensing problems such as dripping, stringing, pattern definition, and have confirmed our results with experiments using high-speed dispensing equipment. Paste dispensability is described by a three parameter model; yield point Y, viscosity index E, and pseudoplasticity index n, which characterizes flow at low and high shear rate regimes. Materials that exhibit different values of Y, E, and n are correlated with their dispensability. This work has lead to improved silver-glass materials that can provide stress relief for large dice, and optimum rheology for high-speed dispensing. © 1990 IEEE