Nickel-based bond pads for wire bonding are emerging as an advanced alternative to the traditional aluminum bond pad with benefits for both gold and copper wire bonding, as well as reducing damage during wafer probe. These pads typically have a two-layer Ni- Pd or a three layer Ni-Pd-Au structure and can be very cost-effectively applied by well developed electroless plating processes. The Ni-Pd-(Au) can either replace the aluminum pad by plating directly on the device's copper metallization or be plated onto existing Al pads. In either case, the electroless process does not require a mask. Skyrocketing gold prices have recently accelerated the conversion of fine pitch devices from gold to copper wire bonding. Although copper wire has been well accepted in large wire diameter, low pin count applications, pad damage caused by the greater hardness of copper relative to gold can complicate the conversion in high I/O (>200) devices. This pad damage may include Al splash, cratering or breaking of fragile dielectrics. Nickel pads are four times harder than aluminum and are shown to virtually eliminate the issues of pad splash and damage, while providing excellent bondability and reliability.
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