Aerospace carbon fibre-reinforced components are cured under high pressure (7 bar) and temperature in an autoclave. As in an industrial environment, the loading of an autoclave usually changes from cycle to cycle causing different thermal masses and airflow pattern which leads to an inhomogeneous temperature distribution inside the carbon fiber-reinforced plastic part. Finally, the overall process can be delayed and the part quality can be compromised. In this paper, the heat transfer in a small laboratory autoclave has been investigated using calorimeter measurements and a fluid dynamic model. A complex turbulent flow pattern with locally varying heat transfer coefficient has been observed. Especially, the pressure and the inlet fluid velocity have been identified as sensitive process parameters. Further finite element simulations with adjusted boundary conditions provide accurate results of the curing process inside of the components for selective process control. The heat transfer coefficient has been found to be almost stationary during the observed constant pressure autoclave process allowing a separated investigation of the heat transfer coefficient and the curing of the components. The presented method promises therefore a detailed observation of the autoclave process with reduced computational effort.

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Within this paper, it is shown that the assumption of transversal isotropy usually applied to unidirectional layers is not valid, if interleaf layers are introduced to increase the impact performance of the material. An approach is suggested to consider the meso-structure of composite materials with interleaf layers in the calculation of the elastic properties, the thermal expansion coefficients, and the chemical shrinkage coefficients. The approach uses known rules of mixture in a first step, to determine the properties of the carbon fiber–reinforced polymer layer as well as those of the interleaf layer and combine them in a second step by new meso-scale rules of mixture. The approach is discussed using known material data and shows to provide plausible results. The effects of the material properties influenced by the meso-scale rules of mixture on the process induced distortions are then discussed exemplary considering the thermally induced spring-in. It is shown that the meso-structure has a considerable influence on the process-induced distortions and cannot be neglected in the prediction of it.

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The fatigue and damage of solder joints as well as the potential for interface failure within chip scale packages (CSP) are primarily caused by thermal loading. The thermally induced residual stresses depend on the thermal mismatch encountered during thermal cycle tests (TCT) and, for power cycle tests (PCT), on the gradient of the temperature distribution. In order to characterize and to model the potential for failure TCTs and PCTs were simulated by stationary as well as transient finite element (FE) heat conduction analyses for various CSP geometries and materials selections (PI-flex, organic and ceramic based substrate). The resulting thermal stresses as well as the irreversibly accumulated energy densities were computed with FE on the basis of time-independent plasticity and explicitly time-dependent secondary creep laws. The resulting data was used together with an energy densitybased damage law to perform a lifetime prediction. The outcome of the computer simulations was validated by suitable experiments (e.g., thermal Moire) and an attempt was made to establish a lifetime-reliability ranking chart. IntroductionThe successful and safe development of increasingly miniaturized microelectronic structures, such as BGA or CSP packages, requires a two-fold validation process based on lab experiments computer modeling. Only the combination of both allows to quickly react to the rapid development of