Effects of Silver Dissolved in Eutectic Gold‐Silicon Solder on Silicon Devices

Abstract

In a die bond system using eutectic Au‐Si solder, stress in the die tends to increase when Au is replaced by Ag as a plating material on Cu alloy leadframes. The Ag dissolution into the solder is proved to be a major cause of fracture or thermal fatigue due to stress increase in bonded Si devices. The piezoresistance effect in a Si chip bonded to a Ag‐plated substrate is also shown to be larger. Thermal analysis indicates that the freezing point of the Au‐Si solder increases with the increase in the Ag content in the solder. Die bonding at a temperature below 380°C is also demonstrated to be effective in lowering the propensity of a die to fracture.