Ar plasma was employed to remove/reduce the oxidation of two typical types of bond pad surfaces, namely aluminum (Al) surface and gold (Au)-coated palladium (Pd) surface, prior to Au wire-bonding process. Field emission scanning electron microscopy (FESEM) and Auger electron spectroscopy (AES) were employed to characterize the bond pad surfaces without and with the plasma cleaning. Processability and reliability results were compared, analyzed and discussed. Although the plasma cleaning did not make significant change for either the Al bond pad surface or the Au-coated Pd bond pad surface in terms of surface morphology, it was found that the impacts of the plasma cleaning on the two types of bond pad surfaces were quite different. On the one hand, for the Al bond pad surface, the Al oxide layer on the bond pad was reduced with the plasma cleaning. However, there was no further significant improvement observed in terms of either the ball shear modes or shear values after wire-bonding process and after stress. On the other hand, for the Au-coated Pd bond pad surface, poor bondability and serious non-stick-on-pad (NSOP) were observed in the initial stage without the plasma cleaning. Its bondability has been improved significantly after the plasma cleaning. Both the shear modes and shear values after the wire-bonding process showed significant improvements for the samples with the plasma cleaning. This is mainly because there was an interdiffusion between the Pd and Au layers; the Pd diffused from underneath to the top of bond pad surface and formed Pd oxide, which degraded the bondability of the bond pad. The plasma cleaning improved the top layer surface condition of the Au-coated Pd bond pad by removing/reducing the Pd oxide.

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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.