Influence of Copper Wire Material Additive Elements to the Reliability of Wire Bonded Contacts

During the past ten years, copper (Cu) bond wires have extensively replaced gold (Au) wire materials. While this development began in the consumer electronics sector, Cu wires are now increasingly advancing into applications with challenging environmental conditions and high reliability requirements, such as the automotive sector. Typically, core material of Cu wire (bare Cu / palladium coated Cu wire - PCC) is 99.99wt% Cu. In order to apply PCC wire to automotive devices, the wire material must meet the demands for long term reliability specific to automobile including stable operation under harsh environment. To achieve this, bonding wire suppliers use small amounts of additive elements in Cu core to enhance the long-term reliability.In the meantime, several types of high reliability Cu wires are available in the market. However, there are only few papers describing/comparing the effect of the additive elements used. The mechanism and progress state of degradation behavior (corrosion) depend on the type of additive element, especially for severe high temperature storage life (HTS) test. Therefore, it is very important to understand the effect of additive elements.We investigated the degradation mechanism of Cu wire bond contacts with different type of additive elements. Subsequently to challenging artifact-free preparation routines, high resolution analyzes (SEM, transmission electron microscopy - TEM, nano-spot EDS, electron beam diffraction - EBD) were carried out on ball and stitch bond contacts to clarify the effect caused by the additives. Mechanical bond tests (pull test) were also performed, and the correlation to the result of micro-structural analyzes were studied. The results of this investigation will be valuable information for the wire users in selecting the optimal wire material required for automotive devices.