Cu and Al-Cu composite-material interconnects for power devices

As power-device technology evolves toward higher power density and devices require longer product lifespans, improving interconnect technologies becomes an increasingly important priority. Several alternatives to the widely accepted aluminum (Al) wire interconnect are being considered. Aluminum ribbon offers the first step of performance improvement in specific applications due to its higher current-carrying capacity and superior heat dissipation and is proven in high volume production. The next level of improvement is aluminum copper (Al-Cu) wire or ribbon. The Al-Cu interconnect can be used with standard Al die metallization with a tested reliability improvement of 4-5 times over Al wire. However, a robust process is yet to be developed that will achieve sufficiently high yields. The final level of performance improvement is copper (Cu) wire and ribbon. Recently it was reported that Cu wire bonding can improve bond reliability more than tenfold over Al wire. Significant technical challenges must be overcome, however, before large-Cu-wire and ribbon bonding is suitable for high-volume production. Testing shows that large-Cu-wire bonding with bond heads made specifically for Cu wire is feasible, but due to the uncertain availability of suitably metallized die, a process assessment of production requirements has not been finalized. This paper examines the relative benefits and challenges of the Al, Al-Cu and Cu interconnect technologies. The results show that Al-Cu could be an attractive solution from a performance and cost standpoint with existing Al based die metallization. Process studies and test results show that many characteristics of Al-Cu are common to Cu bonding, making the process development a stepping stone to affirming the more challenging but higher performance Cu process.