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High temperature viable interconnection realized by sintering nano solder at low temperature
Keywords: nano solder, melting point, depression
The conventional interconnect materials like lead-free solders which cannot survive higher than 200℃ are hindering the progress of extension of wide band gap semiconductors (like SiC or GaN), improvement of functional density, minimization of electronic devices, etc., which need long term reliable interconnection at temperature higher than 300℃. Sintering nano silver paste has been a popular approach during recent years. However, its high cost and long sintering time caused by high melting point drags it back from practical application. This paper comes up with a total novel concept of utilizing the most common IMCs (like Cu6Sn5, Cu3Sn, Ni3Sn4, etc.) in solder bumps as interconnect materials. Taking advantage of nano-size effect (melting point reduces with particle size), the sintering of nano IMCs can be tailored to be compatible with conventional soldering process, not only in the aspect of processing temperature but also time needed. After sintering, the transformation from nano into bulk renews IMCs their bulk melting points, allowing the interconnection to survive higher than 300℃. Coprecipitation reduction is used to synthesize monocrystalline IMC nano particles with diameters around 10nm. The melting point of the product can be 100℃ lower than IMC bulk, which is 5 times better than the reported best data about nano solders. Increasing the amount of Sn precursor produces mixed nano particles of pure Sn and IMC. Thanks to the melted nano Sn particles and its fast reaction with Cu substrate, the interconnection can be realized at 250℃ in a short time, generating a whole IMC bump at meanwhile.
Ying Zhong, PhD Candidate
Harbin Institute of Technology & UCSD
San Diego, CA

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