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A deep analysis of the reliability of lead-free (SnAgCu) solders in comparisonwith tin-lead solders have been done for a particular aerospace application,SwissCube's motherboard (MB). Since 2006, using Pb in consumer electronicshas been banned. Aerospace applications are not included in this legislation,however, sooner or later aerospace industry should comply with the generaltrend in the electronic industry because it is dependent on the whole indus-try for its components. Searching for a lead-free solder which presents high-reliability properties is still continued. SnAgCu solders have become popular inthe electronics industry, because of the price and their mechanical properties.The creep properties of this solder composition, as the most important deforma-tion mechanism under thermal loads, has been investigated in this thesis, andresults have been validated with a thermal shock test. To simulate creep de-formation in 2-dimension, one small electronic package, resistor, of SwissCube'smotherboard was selected. Main constitutive relations have been implementedin a nite-element analysis software, to calculate creep strain evolution underthermal loads. The results of simulation suggest using, the new kind of solder, SnAgCu, would be even better for this type of package. For 3-dimensionalanalysis, one of the largest packages of the SwissCube's motherboard was simulated, using a conservative assumption in terms of constitutive relation from 2-dimensional analysis. The risk of failure for this package is not high, and itwas not predicted to see a total failure after one thousand test cycle. Again,both solders show a good resistance to creep deformation, although SnAgCushows a higher number of life cycles to failure from simulation results. Finally,a thermal shock test was performed to evaluate the reliability of solder joints practically. The test was performed for one thousand cycles. Temperature andoutput current were monitored. No cut in voltage was seen, while temperaturefollowed a very close trend to thermal simulation result. Microstructural analysis has also been performed using metallography process and optical microscopy.Results of this investigation also shows that both solders are safe to be used upto one thousand cycles. Overall, both solders are highly reliable with this number of thermal cycles, however, SnAgCu shows higher life time under this typeof loading.

Le SwissCube est le premier satellite suisse à être parti dans l’espace. Il fait parti de la famille des picosatellites, c'est-à-dire les satellites dont la masse est de quelques centaines de grammes.Ce travail consiste en la révision et l’amélioration de la mécanique d’un système composé d’une roue d’inertie et de son moteur.

The overall goal is the development of a new control software for the inertial wheel assembly of the SwissCube project. SwissCube is an educational project of several Swiss universities and technical colleges under the supervision of the Space Center of EPFL1. The SwissCube is a pico-satellite which respects the CubeSat standard and is almost entirely built by students from the different participating universities. The inertial wheel assembly (IWA) is composed of the IWA motor, the inertial wheel itself and the command electronics. The system fulfills two functions at the same time: • Stabilization of the spatial orientation of the satellite using the gyroscopic effect (used as a momentum wheel) • Controlled rotation of the satellite around the axis of rotation of the IWA for compensation of in-orbit perturbations as well as reorientation (reaction wheel mode)

Future space exploration will emphasize on cost effectiveness and highly focused mission objectives. Missions costs are directly proportional to its total weight, thus, the trend will be to replace bulky and heavy components of space carriers, communication and navigation platforms and of scientific payloads. MEMS devices are ideally suited to replace several of these components in the future, first by substituting larger and heavier components (e.g. a gyroscope), then by replacing entire subsystems (e.g., inertial measurement unit), and finally by enabling the microfabrication of highly integrated picosats. This progressive approach will also enable new mission scenarios and more detailed investigations of the space environment and of planetary surfaces. Very small satellites (1 to 100 kg) stand to benefit the most from MEMS technologies because reaching the desired performance levels is only possible using a highly integrated approach. The small satellites are typically used for science or technology demonstration missions, with much higher risk tolerance than multi-ton telecommunication satellites. In addition, the ability to mass produce MEMS components opens a new approach to space exploration in the future by sending constellations of nano and picosatellites into space. Examples of such miniaturization and successful use of MEMS for space and planetary missions are described in this paper.