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Microelectronics are being required to show high reliability within aero-engines, oil-gas wells and other extreme applications where devices can experience over 250°C, 1000bar, corrosive environments and significant vibration. Currently operation may be only possible for a small number of hours, which necessitates expensive shut-down and replacement. Wire bond interconnects continue to be critical to overall reliability though previous studies have shown that traditional Au-Al bonds fail in such environments due to microstructural instability. Au-Au bonds offer a potentially stable solution that is increasingly desirable as microelectronics are required to endure ever harsher conditions. Au ball bonds on two representative substrates with Au surfaces and ceramic bases have been exposed to 250 and 300°C in N2 for up to 2000 hours. Substrate 1 was a high temperature co-fired ceramic (HTCC) with a Au coating above Ni-Co and W layers, and Substrate 2 was a Au thick film on alumina. Wire pull and ball shear tests for both sample types significantly exceeded industry specifications, though a decrease in yield strength was observed. Key samples were cross-sectioned and grain structure was revealed by ion channelling contrast within a focused ion beam (FIB) system. The yield strength decrease was attributed to the Hall-Petch effect through elimination of twin grains formed during bonding deformation. Electron probe microanalysis (EPMA) of underlying Ni showed little interdiffusion into the Au. Hence the mechanical robustness and microstructural stability of Au-Au wire bonds in extreme environments has been demonstrated and understanding of thermal ageing mechanisms has been improved.

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Silicon on Insulator (SOI) device technology has been shown to be capable of functioning satisfactorily at operating temperatures of >200°C. Most of the applications to date have required performance for short times (<2,000 hours) at the highest operating temperatures of up to 225°C in down-well drilling applications. There is interest in extending the endurance of high temperature electronics into aero-engine and other applications where a minimum 20 year operating life is stipulated. In order to gain confidence in high temperature electronics that can meet this requirement, accurate reliability data are needed and end of life failure modes need to be identified. Most of the reliability data on the high temperature endurance of the integrated circuit is generated with little consideration of the packaging technologies, whilst most of the reliability data pertinent to high temperature packaging technologies uses test pieces rather than devices, which limits any conclusions relating to long term electrical performance. This paper presents results of temperature storage and cycling endurance studies on SOI devices combined with high temperature packaging technologies relevant to signal conditioning and processing functions for sensors in down-well and aero-engine applications. The endurance studies have been carried out for up to 11,088 hours at 250°C, with functioning devices being tested periodically at room temperature, 125°C and 250°C and rapid thermal cycling from −40°C to +225°C. Different die attach and wire bond options have been included in the study and the performance of several functional blocks on the SOI device has been tracked over the endurance tests. The failure modes observed on completion of the endurance tests include die cracking and deterioration of the device bond pads accelerated due to degradation of some die attach materials. The routes to achieving stable long term performance of packaged devices at temperatures of 250°C will be outlined.