Cu-Al Intermetallic Growth Behaviour Study Under High Temperature Thermal Aging

Abstract

Copper (Cu) wire always gains the population in semiconductor industry for its superior thermal and electrical performance with increase of gold wire price in the market. The expanding use of electronics components in automotive electronics and rising in high reliability requirement are stimulating vigorous research and development on intermetallic (IMC) growth at the interface between Cu wire bonded ball and Aluminum (Al) bond pad metallization. In microelectronics packaging, IMC is an essential for interconnect formation between bonding wire and bond pad metallization. It grows during other assembly processes. Cu-Al intermetallic grows slowly and perceived higher reliability performance compare to Au-Al system especially during high temperature storage stress test. However, Cu wire with Al pad metallization formed type of IMC with no or very narrow range of solubility and this type of compound is very strong but very brittle. This study evaluates bare Cu wire bonding on Al pad metallization. As Cu wire IMC is known hardly observed at T0 after wire bonded, evaluation samples were subject to thermal aging to promote the IMC growth in un-molded strip form. Preliminary responses e.g wire pull, ball shear strength were collected. IMC coverage were analyzed and its growth thickness were examined from cross section sample by scanning electron microscopy (SEM) method. The stability of Cu-Al IMC in molded package form was studied under different high temperature storage stress test condition include both 150°C@2000hrs and 175°C@1000hrs. SEM based analysis technique - energy dispersive x-ray spectroscopy (EDX) is used to identify the IMC phases. Aside, transmission electron microscopy (TEM) analysis is adopted to understand IMC growth behavior and phase in depth. IMC thermal driven degradation mechanism was analyzed and discussed. (literature study, bench mark other study)