Cu wire HAST fail mechanism investigation for BGA package

Abstract

The usage of copper wire is becoming more widespread in recent time. However, it is well known that copper wire is more critical compared to gold wire, in terms of wire bond workability and reliability. Especially, during HAST (Highly accelerated stress test) copper wire is sensitive for corrosion of the Cu-Al intermetallic compound (IMC) resulting into ball lift failure. Therefore, the purpose of this paper is to study the root causes for HAST failures with copper wire bonding in BGA packages. Moreover, Cu-Al IMC corrosion is described with reference to recent publications. To increase product robustness against Cu-Al IMC corrosion, the factory environment and process control are important. In addition, the HAST test condition for the BGA packages specifically, is also proven to be an important parameter due to material stability. A combination of high halogen-ions concentration levels (e.g. Cl-) and bias will accelerate the Cu-Al IMC corrosion leading to ball lift failures. One potential source of halogen-ions is the substrate itself. Two different temperatures (110°C, 130°C) which are typical HAST test temperatures, were applied for the chemical analysis of the substrates. From test results, it was shown that extraction at higher temperature will lead to a higher concentration of halogen-ions. This increases the risk for Cu-Al IMC corrosion phenomena. In summary, it was revealed that halogen-ions from the substrate are released at higher HAST test temperature.