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A portative electronic nose is conceived especially to detect several pollutant gases and estimate the concentration of these atmospheric components. The interest of our multisensor system is its entire autonomy, low weight and very small size for embedded applications, and its flexibility. Six commercial gas sensors (Figaro) with interesting cross sensitivity and almost low power consumption are used; a micro-controller equipped with a compact flash memory assures data acquisition, analyzing procedures, and data transfer or storage. The prototype is first validated in laboratory by generating atmospheres containing various concentrations of three pollutant gases (H 2 S, NO 2 and SO 2 ) in the range of industrial areas with variable humidity rate. An excellent group separation for the gas natures is obtained by using a multidimensional data analysis algorithm which also allows concentration determination of the gases.

We report a case study for the optimization of a flip chip based stacked die array test package. We demonstrate the importance of package substrate design and substrate thickness on the processibility and package warpage control. We found that for thin substrates copper balancing of the top and bottom die is crucial. We show the impact of flip chip die thickness and substrate thickness on the die attach of the top die(s) in the stack. Investigations on different top die attach alternatives show that tape die attach can have advantages. We demonstrate the importance of the vertical stack structure (i.e. flip chip thickness) and material selection (i.e. mold compound) on the overall warpage control of the package. The results show that even small changes in the package structure can have large impact on the warpage characteristics of the stacked die package.

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