Quantification of Corrosion on Cu Wire Bonding on Ag-Plated Lead Frame in HCl for Automotive Electronic Application

Abstract

Copper (Cu) wire bonding has been widely used in automotive electronics as an interconnection technology. However, Cu wire bonding faces long-term reliability challenges due to corrosion, particularly when exposed to harsh environments. While the corrosion behavior and mechanisms of bulk-sized Cu metal are well studied, the corrosion behavior of submicron-sized Cu wire bonding in miniaturized components remains unclear. This study investigates the corrosion susceptibility of Cu wire with a 1 mil diameter, bonded to an Ag-plated leadframe in a small-outline transistor (SOT-23) package, commonly used in automotive electronics. The Cu wire bonds were subjected to varying concentrations of hydrochloric acid (HCl), specifically 3 M, 5 M, and 7 M, for exposure durations of 6, 12, and 18 hours. The samples were characterized using a field emission scanning electron microscope to observe the microstructure, and ImageJ software was used to quantify the corrosion of the Cu wire bonds. The findings show that the Cu wire bonding is susceptible to corrosion when exposed to high concentrations of HCl. The corrosion of the microstructure became more severe with increasing HCl concentration and exposure time. The affected area of the Cu wire bonding was 21% after 6 hours of exposure to 3 M HCl, increasing to 100% after 18 hours of exposure to 7 M HCl. This study reveals that the corrosion behavior of Cu wire bonding is a combination of selective and pitting-like corrosion, resulting in localized surface degradation rather than uniform corrosion. These findings provide valuable insights into the corrosion behavior of 1 mil Cu wire bonding in SOT-23 packages under highly corrosive environments.