Au-Sn SLID Bonding: A Reliable HT Interconnect and Die Attach Technology
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A. Background
HIGH temperature (HT) environments offer great challenges for electronic systems. In applications like automotive, aerospace, and drilling and well intervention systems, the electronic components are often exposed for temperatures above 500 K (~200 C). The number of commercially available HT wide band gap semiconductors is rapidly increasing.[1] Silicon carbide (SiC) and gallium nitride (GaN) are commonly considered as the semiconductors of choice for HT applications.[2] SiC has a wide band gap, a high breakdown field strength, a high thermal conductivity, and an operating junction temperature of up to 850 K (~600 C).[2–5] However, lack of qualified HT packaging technologies limits the market growth.[2,6–8] The range of HT die attach and interconnect techniques is restricted.[6,9,10] Alternatives include sintered nanoparticle Ag bonds,[11,12] liquid-based solder bonds,[13] composite solder bonds,[14] bismuth-based solder bonds,[15] Au-Au thermo-compression bonds,[16] and solid–liquid TORLEIF ANDRE´ TOLLEFSEN, Ph.D. Student, is with the SINTEF ICT Instrumentation, 0373 Oslo, Norway, and also with the Institute for Micro and Nanosystems Technology, Vestfold University College, 3184 Borre, Norway. Contact e-mail: torleif.tollefsen@ sintef.no ANDREAS LARSSON, Senior Scientist, and MAAIKE MARGRETE VISSER TAKLO, Research Manager, are with the SINTEF ICT Instrumentation. ANTONIA NEELS, Section Head, and XAVIER MAEDER, Post Doc, are with the XRD Application Lab & Microscopy, Microsystems Technology Division, CSEM Centre Suisse d’Electronique et de Microtechnique SA, 2002 Neuchaˆtel, Switzerland. KRISTIN HØYDALSVIK, Post Doc, and DAG W. BREIBY, Associate Professor, are with the Department of Physics, Norwegian University of Science and Technology, 7491 Trondheim, Norway. KNUT AASMUNDTVEIT, Associate Professor, is with the Institute for Micro and Nanosystems Technology, Vestfold University College. Manuscript submitted December 2, 2012. Article published online January 12, 2013. 406—VOLUME 44B, APRIL 2013
interdiffusion (SLID) bonds.[17,18] The latter, also called transient liquid phase (TLP) bonding,[19,20] isothermal solidification,[21] or off-eutectic bonding,[22] has proven to be an excellent candidate.[22–25] It utilizes a binary system with one low and one high melting point metal. Examples of SLID systems include Ag-In,[17] Ag-Sn,[26] Au-In,[17,27] Au-Sn,[22–25,27–33] and Cu-Sn.[34–37] In the present work, the focus is on the Au-Sn system.
B. Processing A combination of solid-state and liquid-state diffusion takes place during SLID bonding.[33] First, the bonding surfaces are brought into contact and heated to a temperature above the melting point of the low melting point metal, quickly creating new intermetallic compounds (IMCs) by liquid-state diffusion. Second, if the temperature is kept high enough, solid-state diffusion will continue until a uniform bonding layer is obtained.[27] The solidification is isothermal, and the final joint has a higher melting point than the processing temperature. Since
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