The Feasibility of Au Ball Bonding on Sn-Plated Cu

The feasibility of thermosonic gold wire bonding on Cu coupons with Sn/Cu metallizations was studied by evaluating shear strength and microstructure of balls bonded on different Sn metallization samples. The 0.85 ± 0.08 μm and 5.34 ± 0.21 μm thick metallizations were produced by dipping the Cu coupon in 250°C molten Sn solder for 1 s (sample 1) and 30 s (sample 2), respectively. Cu6Sn5 intermetallic compounds are formed during dipping. After wire bonding, Au-Cu-Sn layers are found on the ball-coupon interface of both samples. The highest ball shear force observed was 40 gf (1 gf = 9.81 mN) and was achieved on sample 1 using 520 mW and 40 gf of ultrasonic power and bonding force, respectively. The shear fracture goes through the Au ball. The Sn is squeezed out of the contact zone during wire bonding and forms flashes that extend 5 μm and 25 μm beyond the contact zone for samples 1 and 2, respectively.