This paper presents the microstructures and electrochemical properties of Si-Ti-Ni alloys of various compositions prepared by a rapid solidification process. Si-15Ti-(0-25 at%)Ni alloy ingots prepared by arc-melting was melt-spun to produce thin strip of -15 Om thickness. The Si-Ni-Ti alloy electrode were fabricated by mixing the active powdered materials (88 wt%) with ketjen black (4 wt%) as a conductive material and polyamide-imide binder (PAI, 8 wt.%) dissolved in N-methyl-2-pyrrolidinone (NMP). Results showed that the microstructures of melt-spun Si-Ti-Ni ribbons consist of silicon, TiSi2, Si7Ni4Ti4, and NiSi2 phases depending on the composition. As the content of nickel increased in silicon matrix, TiSi2 phase disappeared while Si7Ni4Ti4 and NiSi2 phases are generated. The cycle efficiency of Si65Ti15Ni20 and Si60Ti15Ni25 alloys was significantly improved because of the increased volume fraction of Si7Ni4Ti4 and NiSi2 phases and fine particulated silicon phase.
Presently, Sn-Ag-Cu (SAC) solders are most commonly used as the interconnect materials in the semiconductor package. However, their thermal fatigue and drop impact resistant properties depends on the Ag content and therefore, most semiconductor package assemblers are forced to implement multiple SAC alloys depending on intended performance. Sn-xAg-Cu solders with high Ag content (x>3 mass%) give good temperature cycling (TC) reliability but poor drop impact reliability whereas Sn-xAg-Cu solders with low Ag content (x<2 mass%) show poor temperature cycling reliability but good drop impact reliability. So, there is need to develop solders having both good TC and drop impact reliability. For the present study, we developed a new SAC solder by micro-alloying it with Ni and Bi. It was found that the thermal fatigue and drop impact resistant is improved dramatically simultaneously. The improvement in the drop impact resistance is attributed to the decrease in the bulk and joint IMC thickness and grain refining. The high TC reliability is due to the unique network like structure of Ag3Sn in the bulk solder microstructure. The newly developed solder show high and stable shear and pull strength as compared to SAC solders and the dominant fracture mode in the high speed shear test is ductile. This new solder has potential to become interconnect material for all types of semiconductor packages. IntroductionSn-Ag-Cu solder is most common interconnect material used in electronic devices. However, their thermal fatigue and drop shock reliability performance depends on the Ag content in the solder. High Ag content (≥ 3wt%) solder shows better thermal cycle reliability performance and poor drop performance whereas low Ag content solder (≤ 2wt%) shows just opposite performance [1,2].For devices such as computer, fax, printers etc., which requires high thermal cycling performance, high Ag content solders Sn-3.0Ag-0.5/0.7Cu are used. For handheld devices (mobile, digital camera etc.), low Ag content solder Sn-1.0Ag-0.5Cu is used.The present and future electronic devices are getting miniaturized while their functionality is continuously increasing. These devices require solders having both good TC and drop impact reliability. So, there is clear need to develop solders which satisfy reliability requirements in all conditions. It is well known that adding minor dopants in the normal SAC solders can enhance their mechanical properties and reliability. Following extensive research and experimentation, we developed the Ni and Bi doped novel SAC solder. The solder composition chosen for this study was Sn-2.5Ag-0.8Cu-Ni-Bi. In the present study, we evaluated the
The phase change due to varying content of titanium in Si-Ni-xTi alloys and its effect on the electrochemical behavior has been investigated. Specimens were prepared by melt-spinning to reduce the microstructure scale. Results showed that silicon particles of 50-100 nm diameter and dendrites of somewhat larger scale were formed in the Si-Ni-Ti alloys ribbons. The microstructure of Si70Ni15Ti15 alloy ribbons was composed of silicon particles finely dispersed in Si7Ni4Ti4 phase. The cycle performance was improved by the formation of TiSi2 or NiSi2 phase at the presence of Si7Ni4Ti4 phase, either of which combined with Si7Ni4Ti4 phase effectively accommodated the volume change of silicon particles during cycling. The reduced scale of silicon particles contributed to the enhanced cycle efficiency as well.
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