Abstract:
Electronic designers have been moving towards higher part density in multi-chip modules (MCMs) for aerospace applications. This density can be achieved by combining multiple functions on a single die, including more dice in one package (single substrate) and by extending the substrate (die-to-die interconnect) into the z-direction. As density increases, the number of inputs and outputs increases, creating a wire bond configuration that is driven by minimum distances between the bond pads on the die and those on the package. This creates long wire bonds in the x-y plane. Stacked dice will have long bond wires in the z-direction.
The fracture strength of aluminum wire is well understood because the material is a standard construction material throughout the industry. Gold alloy wire is manufacturer unique, and the exact composition and quantity of the additives is considered proprietary by most (if not all) of the manufacturers. These additives are in the 10 ppm range and are used to enhance elongation, heat affected zone (HAZ) characteristics, and tensile, fatigue and fracture strength. The presence of the additives makes it very difficult to predict the fatigue strength of the gold wire used to make long bond wires, and this limits one's ability to predict the electronic part's reliability. Knowing the susceptibility of long bond wires to fatigue fracture and their resonant frequency will enable reliability predictions of electronic system that may be exposed to shock and vibrations.
Related Project(s):
EPAC (Electronic Packaging)
Related Area(s) of Emphasis:
Advanced Interconnect Reliability
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