Solid state interfacial reaction of Sn-3.5Ag solders with Ni-P and Ni-W-P under bump metallization

Abstract

(Ni-P and Ni-W-P) were developed as the soldering metallization in this work to solve the potential reliability. The interfacial reactions between lead-free Sn-3.5Ag solder and these ternary metallizations during reflow and thermal aging were investigated. The interfacial reaction between the same solder and electrolessly-plated binary NiP metallization was compared to understand the effect of the addition of the ternary element. Among all four types of metallizations, NiP is consumed at the fastest rate, while Ni-W-P is consumed at I would like to take this opportunity to acknowledge the guidance, support, and assistance received during this work. First of all, I sincerely express my great gratitude to my supervisor, A/P Huang Yizhong, for his invaluable guidance, advice, and encouragement throughout the course of this study. I would also like to thank Dr. J. N. Balaraju and Dr. K. Chen for their advices on electroless plating. Without their supervision and constant support, this work could not be accomplished. SEM Scanning Electron Microscopy TEM Transmission Electron Microscopy XRD X-ray Diffraction 1.1 Background and motivation Recently bonding and soldering are widely used in interconnect technologies in the packaging industry. Between these two methods, soldering is an area array technology which could potentially provide higher input/output (I/O) density, as compared to wire bonding, which is only used in peripheral joining. For solder joint, it provides not only electrical but also thermal connection in an electronic device1. According to this, its reliability is much more important due to its critical importance. Because the failure of a single solder joint will lead to the failure of the electronic device, sometime even the entire system. As the trend which electronics industry tends to increase higher I/O counts and smaller feature size, coupled with more strict restriction on materials toxicity (e.g. lead-free), the packaging industry faces ever greater challenges with regards to the interconnect reliability in the coming decades. As compared to other inventions, flip chip soldering technology has already been proven to be a promising technology to cope with these challenges. This reaction proceeds very fast and its duration is short, i.e. around 60s. While during service, solid-state reactions occur at temperatures which is lower than the melting point of solder. Liquid-state reaction proceeds much faster than solid state reaction, but solid state reaction has a longer duration. In both liquid-state and solid-state reactions, Intermetallic compounds(IMCs) form and continue to grow at the solder/metallization interface. The formation of IMCs is reported to achieve good metallurgical bond, but the excessive growth of IMCs has the ability to Lots of research effort has been done to slower the interfacial reaction to maintain the good wetting between solder and the metallization [1,2,10]. One approach is to change composition of solder by adding different elements into the solder alloys. However, this ap...

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