Accelerated Incoming Thermal Soak Verification Procedure for Sensor Lots
Accelerated incoming thermal soak verification exposes latent transducer parameter drift within 48 hours, enabling quantitative C=0 lot rejection before production integration.
Wire Bond Kirkendall Voiding
Structural Defect
Formation of microscopic holes at the interface between different metals in a wire bond. Wire bond kirkendall voiding occurs when the atoms of one metal migrate faster than the atoms of the other metal. This imbalance leaves behind vacancies that coalesce into large gaps over time.
Atomic Migration
Heat provides the energy required for the gold and aluminum atoms to swap positions. In wire bond kirkendall voiding, the gold from the wire and the aluminum from the pad diffuse at different rates. This process creates intermetallic layers that are mechanically weaker than the original metals.
The voids typically grow during high temperature storage or operation.
Electrical Failure
Porosity at the bond interface reduces the contact area and increases the electrical resistance. Wire bond kirkendall voiding can eventually lead to a complete separation of the wire from the pad. This causes an open circuit and the failure of the electronic package.
The defect is a known reliability concern in gold-aluminum bonding systems.
Mitigation Strategy
Selection of alternative materials or the use of dopants can slow down the diffusion process. Wire bond kirkendall voiding is minimized by using copper wire or by adding small amounts of palladium to the gold. Manufacturers also control the bonding temperature and pressure to create a more stable interface.
Verification of the bond integrity is performed through pull tests and cross sectional imaging.