Abstract
An important characteristic of gold ballbonds is intermetallic coverage (IMC), defined as the percentage of the total area on which gold aluminide compounds are formed by reaction between the gold ball and aluminium alloy metallization during thermosonic bonding. IMC measurement complements mechanical measurements such as ball pull and shear strength and in general, IMC should be maximised to aid in achieving a high degree of initial mechanical robustness so that devices can withstand subsequent processing steps and maintain high reliability. Too little IMC can result in weak bonds and erratic intermetallic growth patterns during subsequent thermal processing of bonded devices and may result in mechanical and electrical malfunction and failure. Optical microscopy of the underside of ballbonds is often used to determine IMC, but usually without consideration of certain key physical effects such as lighting, resolution and surface roughness. This paper compares the relative merits of IMC measurement by scanning electron microscopy (SEM) and optical microscopy and includes practical guidelines for the use of each technique.
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Mr Frank Wulff is Manager for Materials Development & Characterization at Kulicke & Soffa's bonding wire R&D facility in Singapore and has been with K&S for 10 years. Prior to joining Kulicke & Soffa, Mr Wulff worked in industrial failure analysis and materials characterization for CEM Research Institute (Now Fraunhofer) for 6 years. His research interests include materials design, characterization, materials processing and reliability.
Dr Christopher Breach is currently Global Director of Applications and Field Service Operations for RVSI LLC, a leading US based manufacturer of automated optical imaging systems used in 2-D and 3-D inspection of microelectronics packages and wafers in the semiconductor industry. He is currently based in Singapore. Prior to joining RVSI he was Director of R&D and Product Development for Kulicke & Soffa's bonding wire R&D facility in Singapore for 41/2 years and in the previous 9 years held university and industry based positions in the areas of physics of interfaces, contact and fracture mechanics, manufacturing and materials process science and technology in Singapore and the United Kingdom. Dr Breach's current technical and research interests are focused on the science and industrial applications of optical inspection and metrology. He remains actively engaged in studies of solid state chemistry, physics and metallurgy of intermetallic compounds, inorganic alloys, microalloys and polymer physical chemistry.
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Open Access This is an open access article distributed under the terms of the Creative Commons Attribution Noncommercial License ( https://creativecommons.org/licenses/by-nc/2.0 ), which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
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Wulff, F., Breach, C. Measurement of gold ballbond intermetallic coverage. Gold Bull 39, 175–184 (2006). https://doi.org/10.1007/BF03215551
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DOI: https://doi.org/10.1007/BF03215551