To replace conventional Al heavy wire bonding in interconnecting power devices, we have explored the use of Cu heavy wire bonding, which offers superior electrical, mechanical, and thermal properties compared to Al wires that leads to better interconnection reliability. Chip pad metallizations that are strong enough to support Cu wires firmly against chip pads and endure high bonding parameters were first evaluated by 3D finite element modeling (FEM) of the Cu heavy wire bonding process. The FEM results indicated that an electroless plated Ni layer may be used as the primary candidate for the pad metallization of Cu heavy wire bonding because it enables the reinforcement of standard Al pads in power devices and allows for metallurgical interaction with Cu wires. Further, the deposition of the Ni layer entailed a simple protocol. The three major bonding parameters including force, ultrasonic energy, and time were optimized to achieve successful wire bonding of 300-μm-thick Cu wires to pads strengthened with Ni layers in power devices. Microstructures and compositions of the bonded interface were analyzed by transmission electron microscopy, which provided insight into the bonding characteristics between the Cu wires and the Ni pads. Reliability tests of the bonding were also carried out by the thermal shock test and pressure cooker test.
Recent Low Temperature Solder of SnBi and Its Bonding Characteristics