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Nanoparticle Enhanced Solders for High Temperature Reliability
Keywords: lead-free solder, nanoparticles, reliability
EU environmental legislation has removed lead from most electronics, and may lead to elimination of lead from even high temperature electronics by 2010. Oil and gas drilling equipment manufacturers face problems as the drilling equipment needs to work in ever deeper and hence hotter environments (150-225C). Other industries, such as automotive and aerospace which deal with high temperature operation face a similar situation. SnAgCu and SnCu as alternatives have been used in industry as replacement for lead-based solder, but are not suitable for high temperature operation without modification. This paper describes the use of 100-300 nm silica nanoparticles to improve the reliability of lead-free solders by increasing creep resistance. Nanoparticles are composed of a silica core and Au metallic shell to ensure solder wettability. To prepare the nano-composite solder, nanoparticles were suspended in a solvent compatible with the flux, and then mixed with the flux, which is finally mixed with the Sn-3.8Ag-0.7Cu (SAC) solder powder to form a solder paste. The mixture was mixed mechanically to prepare a homogenous paste. A relatively new cross section polishing method has been developed using an Argon ion beam to prepare an atomically flat surface, revealing any embedded nanoparticles. Scanning Electron Microscope (SEM) has been used to observe the microstructure of lead-free solders and to detect the nanoparticles. Assemblies prepared using the nano-composite solders are currently being tested for reliability under a temperature cycling regime of 180 C ambient and high temperature storage at 180 C.
Omid Mokhtari, Student
Kings College of London
London, England WC2R 2LS,

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