Experimental part
Choice of experience and design
The testing method is based on a previous study -- named MEMS-REAL -- from CSEM on the reliability assessment of MEMS-based components for space applications. A new method was developed, based on ESA and US military standards, for components that are to be dedicated for space applications. The method from MEMS-REAL is explained in the following paragraph.
Initially, a restricted set of five samples are tested over cycles with increasing load (i.e. 20% greater temperature range, vibrations intensity, etc.) starting from the manufacturer's nominal range of operation, until complete failure occurs. This first step is necessary to define the limit to which the devices can be pushed to. The load can be provided by thermal cycling, thermal shocks, mechanical cycling (i.e. vibrations), mechanical shocks or pressure cycling. These stress tests are chosen in order to represent, as well as possible, the conditions that the device will undergo during spaceborne operations. The second step consists in the application of a load that represents 25% of the maximum value obtained from the first test. This time, 20 samples are necessary and one evaluates of the number of cycles necessary to reach 100% of failure of the devices under a given unique load. A Weibull statistics is then drawn and the characteristic lifetime of the chosen device is defined.
MEMS-REAL's method features three drawbacks:
- a great number of samples is needed for each company willing to evaluate and then qualify a product for space,
- performing of time consuming experiments on this large number of samples,
- no consideration of possible interactions.
These points can supposedly be mitigated by a good design, hence the choice of a Plackett-Burman design as exploratory test plan. This report therefore aims at verifying the applicability of the design of experiments to MEMS reliability assessment.
Test vehicle
Japanese manufacturer Murata is producing the SCA-3100 with capabilities summarized in Figure 2: