Ultrasonic Bonding Property of Aluminum Wire for Power Conversion Module of Automotive

Abstract

This study verified ultrasonic bonding reliability of 15 mil and 6 mil aluminum wires for power conversion module of automotive. Aluminum wires were bonded on aluminum metalized Si chip using by ultrasonic bonding process. To confirm their joints reliability, high temperature and high humidity test (TH) and thermal shock test (TS) were conducted. TH was tested at 85±3 ℃, 85±3 RH for 1,000 h. TS condition was-40~ 125 ℃, 10 min dwell time at each temperature for 1,000 cycles. Before and after the tests, wire ball shear strength and wire ball pull strength of each wires were measured and compared to the degradation rate of bonding strength. Based on these results, bonding strength degradation rate of TS was 10 times faster than that of TH, and TS was more effective test method than TH. Ultrasonic bonding layer crack was generated at the interfaces between Al wire and Al metalization layer of Si chip surface, and propagated along the interfaces.

Recent Progress in Transient Liquid Phase and Wire Bonding Technologies for Power Electronics

“…However, at a wire diameter of 381.0 µm, the tensile strength of the wire was smaller than the bonding strength, and the bonding strength could not be measured. Therefore, this method works accurately for the thinner wire diameter [115].…”

“…The fine aluminum oxide particles grind and polish the surface, leading to a well-exposed layer on both sides. Figure 13 shows the cross-section image of the Cu-wire wedge bonded at the ultrasonic power of 325 mW for 50 ms [115]. The recrystallized grains can be observed in the central zone ( Figure 13a,b).…”

“…These elongated grains are formed during the drawing process of Cu wire due to the frictional heating and normal compressive force induced by ultrasonic vibration along the faying surface leading to the recrystallization of grains. The driving force of the recrystallization, ∆E, between the deformed and recrystallized state is determined by the dislocation density or the sub-grain boundary energy according to the following equation [115]:…”

“…Various reliability issues of wire bonding have been reported. Park et al [115] studied Al wedge bonding using 152.4 µm and 381.0 µm thick wires bonded to an Al-metalized Si chip. The reliability testing was conducted at high-temperature high humidity tests (TH) (85 ± 3 • C, 85 ± 3 RH for 1000 h) under a thermal shock (TS) range of −40-125 • C, 10 min.…”