A novel fluxless soldering process is presented, that enables lead-free soldering o f semiconductor die-bheat spreader (and heat spreader-tu-heat sink structures) at room temperature. The process is based on the use of reactive multilayer foils to locally melt the solder interface. Silicon-copper samples joined with indium solder are thermally characterized for a range of die sizes and bond line thicknesses. The thermal resistance of the solder joints is found to be an order of magmtude lower than for conventiond t h e d interface materials (TIMs), with good thermal fatigue resistance. The predicted thermo-mechanical behavior of the solder interface in a central processing unit (CPU) application indicates that such joints would survive application environments without causing die cracking. The soldering technology employed could greatly enhance the thermal performance of power IC packages such as CPUs, by enabling the adoption of a solder-based TIM between the die and integrated heat spreader.

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SUMMARYHigh-resolution finite volume schemes based on a novel reconstruction technique, SDWLS (solutiondependent weighted least squares) are considered. The SDWLS technique, originally developed for second-order variable reconstruction by Mandal and Subramanian (Appl. Numer. Math., 2007; DOI: 10.1016 DOI: 10. /j.apnum.2007, is further extended to third-order reconstruction with compact stencils involving only the nearest neighbors. The new schemes are applied to solve a few numerical test examples, involving scalar conservation laws and the system of non-linear gas dynamics equations, in order to study their performance. Significant improvements in solution accuracy have been achieved with the secondand third-order SDWLS reconstruction techniques.