Kirkendall Voiding

Diffusion Mechanism

Copper atoms diffuse into the aluminum phase faster than the aluminum atoms can migrate in the opposite direction. This imbalance leaves behind vacant lattice sites that coalesce into microscopic pockets along the original weld line. These pockets grow larger with continued thermal exposure.

Weld Integrity

Electrical resistance across the tab-to-busbar connection increases dramatically as the effective contact area shrinks due to void coalescence. The weakened joint also becomes highly susceptible to fracture under mechanical vibration. This susceptibility increases the risk of cell connection failure.

Prevention Technique

Barrier coatings or nickel plating on the copper tab prevent the direct interdiffusion of the copper and aluminum atoms. This barrier eliminates the vacancy flux that drives the void formation. Choosing the correct plating thickness preserves joint reliability over the pack lifetime.