The reliability performance of copper wire bonding BGA package by way of HAST methodology

Cu wire bonding technology is increasingly being used for the various IC packages from consumer application to high-reliability electronic products due to cost reduction consideration as well as electrical and thermal performance improvement in comparison with Au wire bonding. Despite these positive impacts of the improvements, the reliability still needs to be correctly assessed by the industry in a quantitative manner due to uncertain materials and assembly process issue. In the study, multiple Cu wire types and wire bonding process conditions are designed to validate assembly integrity based on Lead free BGA package with 14×14 body size and 384 I/O. Two bonding wire manufacturers provide the copper wire and palladium coated copper wire used for evaluation. Green molding compound free of halogenated flame retardant with known chloride content is used to mold the BGA package. After process characterization is verified based on wire pull and bond shear test. A HAST methodology (Highly Accelerated Stress Test) is applied to validate the BGA package reliability for the understanding of corresponding materials interaction among the wire material, molding compound and bonding pad metallization due to the acceleration stress drive from the temperature and humidity and bias voltage. In this task, there are five HAST conditions executed including 130°C/85RH%, 130°C/55RH%, 110°C/85RH%, 120°C/60RH% and 85°C/85RH% under 5.5 volt bias. Various temperature and humidity represent relative stress factors to accelerate the test to fail, as well the 3 stress factors usually influence the ionic ingredient in the molding compound to react with Cu wire and pad metallization. There are 4 daisy chain loops designed to monitor electrical resistance after each time period set in one BGA package for the failure judgment when resistance is fully open. Base on the HAST result and following failure analysis, the effect of testing duration, temp- rature and humidity differences and mold compound type are discussed.