A study on Pd distribution effect on the reliability of Au coated PCC wire bonding

Copper (Cu) wire has been widely used in semiconductor packaging for more than 15 years with several advantages such as lower cost, higher electrical conductivity and slower Cu/Al intermetallic compound (IMC) growth than those of Au wire. Furthermore, recently industry requires severe reliability test condition for automotive device so that Cu wire bonding is being highlighted.However, one of disadvantages in Cu wire bonding is Cu/Al IMC can be easily attacked by moisture and sometimes we observe open failure at the interface of bonded ball and bond pad due to IMC corrosion at unbiased highly accelerated stress test (u-HAST) or biased highly accelerated stress test (b-HAST). Many studies have been performed to delay those failures and we come to know that Pd distribution of free air ball (FAB) and bonded ball in Pd coated wire bonding is one of important factors. Our expectation is wide & uniform Pd surrounding on FAB & bonded ball will give us delay in failure. In this evaluation, we tried to find out optimum Electronic Frame Off (EFO) condition such as EFO current & time and to have wide Pd layer distribution to cover whole bonded ball surface because we believe Pd is generally known to protect moisture or halogen attack at reliability test.In this experiment, Amkor standard test die was attached on a laminated substrate and wire bonded using various Au coated PCC wires and encapsulated with epoxy molding compound (EMC). The reason that we selected Au coated PCC is that this wire is Amkor's first recommendation among Cu wires. Optimum EFO condition was verified through Pd distribution result. Parts were undergone u-HAST (130'C/85% RH) up to 800hrs until we see massive failures and failure analysis was done by SEM/EDX mapping to find out the root cause and understand the failure mechanism.Through this study, we could find out optimum EFO condition to have uniform & wide Pd distribution and finally we could pass very severe reliability test criteria over than industry requires. This guideline will be very helpful for Cu wire bonding to the industry.