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In the past, a large number of material models for Sn-based solder alloys have been proposed, which are usually calibrated based on the material testing under isothermal the conditions. However, their ability to map the lifetime differences depending on the temperature rate under the field and test-lab conditions, as well as on the mean operating temperature, is still not completely investigated and validated. The novel thermo-mechanical fatigue (TMF) measurement set-up is employed for in-situ measurement of the material degradation driven by temperature cycles. The experimental system involves different materials, which impose thermally induced displacements onto the solder interconnections. The acceleration of the test duration can be controlled by the placing the sample into the loading positions with the different level of the thermally induced displacement. The measurement enables monitoring of the force-reduction and the concurrent change of displacement. In the current study, the samples comprising a real-scale geometry of the four Ball Grid Array (BGA) connections were stressed with the temperature cycles relevant for the typical lab-tests and field conditions. The level of the thermally induced shear displacement in the solder joints was significantly higher than in an Engine Control Unit ECU. Since the experimental set-up includes various geometrical and material features, an extensive FE-based sensitivity study has been performed. The simulation of the free-expanding system as well as of the system with different pre-characterized dummy samples (without solder joints) revealed the capabilities and specific mechanical behavior of the experimental set-up. Finally, for Sn96.5Ag3.0Cu0.5 solder alloy the ability of the different material formulations to reproduce the trends of the measured hysteresis was analyzed: for double power-law creep model (DPL), unified inelastic strain formulation by Anand, and unified visco-plastic model proposed by Chaboche. Their accuracies in predicting of the acceleration factor between the different temperature profiles are summarized and discussed

The challenges to select materials for the development of electronic modules are aligned with the product requirements, like load condition during operation time, and economic aspects, like processing costs. Often these requirements based on different load types are contradictory, which makes the selections very difficult. This paper is focused on the thermally-induced thermo-mechanical load in the solder connections. In order to improve of the material selection, the authors have developed a setup enabling a cost-efficient material characterization. By testing electronic devices it is not possible to separate the ageing of the solder material from degradation of the incorporated plastic materials. The current setup significantly reduces the order of the influencing materials. Further advantage of this equipment is to design an acceleration level not by the increase of the temperature stroke, but by adaption of the displacement level. The principle of the setup is focused on the accelerated thermally induced mechanical load imposed onto specimen during thermal cycling. The load frame placed in a conventional temperature chamber consists of two metals, frame and core. This construction causes a thermal mismatch which is either induced onto the specimen and onto the incorporated force sensor as well, because this is connected in series. The intensity of the force signal represents the mechanical resistance of the specimen against the enforced displacement. Simultaneously, two contactless displacement sensors integrated into the system close to specimen measure the relative frame-core deformations in directions in- and out-of-plane. The novel measurement setup was developed by focus on homogeneous temperature distribution and stress free specimen assembly. Further, the setup enables to incorporate an adapted realistic BGA-like solder joint configuration. Since the specimen is connected to the setup with an adhesive, it was necessary to prove a long-term stability of the adhesive connections. The paper will present the setup calibration steps necessary for understanding the unique force-deformation behaviour of the system as function of temperature. Finally, degradation measurements on the BGA-like solder joint specimens for various environmental conditions will be presented