Fabrication processes, like die attachment or plastic encapsulation, lead to thermal stresses in micro-assemblies due to CTE mismatches of the involved materials. In this paper, stress-and strain-sensitive test chips were used to measure in situ absolute stresses caused by die attach and encapsulation processes. Furthermore, deformations of assemblies over temperature were observed by white light interferometry and electronic speckle pattern interferometry.Applying these methods, e.g. the effect of entrapped air in thin adhesive layers of die attach assemblies on the absolute stresses in the silicon chip surface could be observed during cure. The resulting stress offset accounted up to 68 % of the thermal stresses at RT in the assembly. IntroductionAccording to common knowledge, die attach processes of silicon chips on substrates like copper lead frames or BGA interposers lead to high tensile stresses in the chip surface and to a warping of the assembly at room temperature (RT) due to CTE mismatches of the materials [1, 2]. Further on, stress states in the chip surfaces of BGA or PTO packages typically change to high compressive stresses at RT after encapsulation [3,4]. Consequently, stress-sensitive structures like semiconductor Hall-plates in magnetic sensors cause a signal offset or change of sensitivity of the sensors due to the pseudo-Hall effect [4]. The reliability of assemblies is also affected by stress induced phenomena like die cracking, die popping or fatigue cracking in plastic encapsulants [5,6].In this paper, an experimental approach was taken to analyze the influence of glass transition temperature, curing temperature, long term storage at RT, chemical and thermal shrinkage as well as non-linear material behavior of the die attach adhesive and the influence of moisture uptake of package materials on the stress developments in microassemblies.

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The reliability offlip-chip-interconnects is primarily affected by the thermo-mechanical deformation ofthe solder ball or bump, which is a consequence ofthe well-known CTE-mismatch problem. The common approach to determine the stresses and strainsfor reliability predictions in the critical interconnections is the use offinite elements simulations ofthe assembly. Simulation results should be verified by experiments in order to prevent systematic errors. A combination oftests and FE-simulations can help to reduce the simulation errors and to verify the computed results. The objective ofthis work is to apply modern test methods for thermo-mechanical investigations on CSP-andflip-chip-assemblies and to evaluate these quantitatively and qualitatively. Applied test methods were electronic-speckle-pattern-interferometry (ESPI)

This paper presents the design, fabrication and characterization of a novel piezo-polymer-composite membrane actuator, Based on this membrane actuator, a valve for liquids and gases is presented as an application example. In measurements with water, the functionality of the valve was demonstrated for a pressure up to 650 hPa with a maximum flow of 1.5 l/h and a leak rate of less than 4 ml/h in the closed state. Moreover, a novel lowcost fabrication technology was developed that combines laser micromachining and polymer insert casting.

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