Resonant fatigue test performance of battery pack connections using wire bonding

Abstract

Reliable interconnections in electric vehicle (EV) battery packs are critical for performance and safety. Wire bonding enables joining dissimilar materials with minimal heat input but suffers from limited joint strength under vibrational stress. Existing testing standards focus on entire battery packs, lacking direct assessment of bonding wire reliability. This study proposes a novel resonance-based fatigue testing method to evaluate the fatigue resistance of aluminum (Al), silver (Ag), and copper (Cu) bonding wires (200 μm in diameter). Results show that Ag and Cu wires significantly outperform Al wire under high-frequency vibration. At 1 mm amplitude, Al wire failed immediately, while Ag and Cu wires survived ∼200,000 and ∼ 300,000 cycles, respectively. In a 10-million-cycle test at 0.6 mm amplitude, Ag and Cu wires exhibited excellent fatigue resistance, whereas Al wire fractured before 60,000 cycles. SEM analysis revealed severe cracking in Al wire after 30,000 cycles, while Ag and Cu wires showed only minor cracks after 10 million cycles. Although Cu wire demonstrated the highest fatigue resistance, its higher bonding temperature is a limitation, making Ag wire a promising alternative. The proposed method offers an effective approach to assessing bonding wire reliability, aiding material selection for enhanced EV battery durability.