Kazuaki Karasawa

Solder joint reliability of indium-alloy interconnection

Recent high-density very large scale integrated (VLSI) interconnections in multichip modules require high-reliability solder interconnection to enable us to achieve small interconnect size andlarge number of input/output terminals, and to minimize soft errors in VLSIs induced by α-particle emission from solder. Lead-free solders such as indium (In)-alloy solders are a possible alternative to conventional lead-tin (Pb-Sn) solders. To realize reliable interconnections using In-alloy solders, fatigue behavior, finite element method (FEM) simulations, and dissolution and reaction between solder and metallization were studied with flip-chip interconnection models. We measured the fatigue life of solder joints and the mechanical properties of solders, and compared the results with a computer simulation based on the FEM. Indium-alloy solders have better mechanical properties for solder joints, and their flip-chip interconnection models showed a longer fatigue life than that of Pb-Sn solder in thermal shock tests between liquid nitrogen and room temperatures. The fatigue characteristics obtained by experiment agree with that given by FEM analysis. Dissolution tests show that Pt film is resistant to dissolution into In solder, indicating that Pt is an adequate barrier layer material for In solder. This test also shows that Au dissolution into the In-Sn solder raises its melting point; however, Ag addition to In-Sn solder prevents melting point rise. Experimental results show that In-alloy solders are suitable for fabricating reliable interconnections.

Highly selective and sensitive gas sensors for exhaled breath analysis using CuBr thin film

We have examined a p-type semi-conductor CuBr thin film used for sensor devices that indicates the order of sensitivity to ammonia in parts per billion (ppb). The CuBr thin film also indicates excellent selectivity to ammonia among reductive gases, which additionally suggests its capacity for fast quantification of the order of seconds. Moreover, CuBr thin film can be adapted to a high-sensitivity aldehyde sensor by a surface modification. Since the fabrication process of CuBr thin film is compatible with an ordinal CMOS process, there is a potential for development into highly integrated and low power consumption sensor devices. These properties make CuBr thin film a promising candidate as a gas sensing material for human-breath analysis.