Effect of die attach material on heavy Cu wire bonding with Au coated Pd bond pad in automotive applications

Abstract

Copper (Cu) is rapidly gaining an increasing market share as an interconnect material in semiconductor packaging because of its major advantages over gold (Au). When replacing part of the bond pad with a noble metal, Cu bonding wire is of particular interest due to its superior electrical properties, lower cost and higher mechanical properties as compared with Au. Extensive work and analysis are needed at the onset of the packaging development phase to meet the right level of manufacturability and reliability requirement. Wire bond process optimization commonly focus around bond time, bond force and bond power. Other factors generally evaluated for copper wire bonding include incoming bond pad cleanliness, bonding pad surface oxidation, wire oxidation during electronic flame off and forming gas flow rate. A lesser known variable, die attach, is often overlooked in packaging with Cu wire. However, die attach (DA) materials that have comparatively low modulus and high elastic properties at elevated temperature (above Tg) can cause problems at wire bonding process temperatures. In this paper three DA material types were evaluated using 50 um Cu wire bonding and main focusing responses of non stick on pad (NSOP) and ball shear strength (BST) as well investigates various process factors in achieving a reliable Cu wire bonding on heavy Cu wire bonding with Au coated Pd bond pad in automotive applications. The results showed that a significant influences from the DA material properties which affecting the wire bonding performance. DA Soft solder are better due to solder has higher elastic modulus (MPa) in even remain at higher bonding temperature. However Polymeric DA1 has comparatively low modulus and high elastic properties in elevated temperature can cause NSOP and low ball shear in smaller chip sizes at higher bonding temperature.