Electrical stability test methods

Electrical-stability testing is essential for conductive adhesives used for electrical connections. Electrical conductivity can degrade at elevated temperatures, on aging with or without power, and on exposiue to humidity and temperature. The specific test method used depends on the application. One test used for die-attach adhesives specified in NASA MSFC-SPEC-592 (now inactive) involves a series of gold-plated Kovar tabs attached with conductive epoxy to metal pads on an interconnect substrate. In the test vehicle, a bias of 5 V and cmrent density of 139 3.9 A7cm (900 A/in ) are applied to a series of wire-connected tabs, and the resistance change is measured after exposure to 150 °C periodically up to 1,000 horns. The maximum allowable resistance change is 5%. 

The test methods covered in this chapter are those most closely related to adhesives for die and substrate attachment, surface-mounting of components, underfill, and optoelectronic assembly. Some tests, such as bleedout and electrical stability, for which there are no standard test methods, are not covered but information for these procedures was already addressed in other portions of this book, for example, in Sections 2.1 and 6.1. 

Standard Test Method for Constant-temperature Stability of Chemical Materials Standard Test Method for Arrhenius Kinetic Constants for Thermal Un.stable Materials Standard Test Method for Rapid Thermal Degradation of Solid Electrical Insulating Materials by Thermogravimetric Method Standard Test Method for Autoignition Temperature of Liquid Chemicals Standard Test Method for Specific Heat of Aircraft Turbine Lubricants by Thermal Analysis Standard Test Method for Linear Thermal Expansion of Solid Materials by Thermodilatometry... 

Chemical vapor deposition (CVD) was applied to produce homogeneous thin films of pure and doped spinel cobalt oxide with similar morphology on the surface of planar and monolithic supports. The planar substrates were used to investigate the thermal stability and the redox properties of the spinel using temperature-programmed methods monitored by emission-FTIR spectroscopy, while the monolithic substrates were used to test the catalytic performance of the deposited films toward the deep oxidation of methane and to evaluate its durability. The high performance of cobalt oxide to oxidize methane in diluted streams was demonstrated at 500 °C. Furthermore, controlled doping of cobalt oxide layers with suitable cations was demonstrated for nickel as an example, which resulted in substantial increase of electric conductivity. 

Three electric waveforms were used throughout the testing. A 100-Hz, +300/-60 V sine waveform (semi-bipolar, 4.5/-0.9 kV/mm) was used with a 20 MPa preload for the accumulation of cycles. Two 10-Hz waveforms were used to evaluate performance changes at a specified cycle number that involved smaller positive peak-values, +200/0 V (unipolar, +3.0/ 0 kV/mm) and +200/-60 V (semi-bipolar, +3.0/-0.9 kV/mm), and successive preloads of 0.7, 20, 0.7 MPa. The 0.7 MPa preload, the minimum allowed load to stabilize the stack, was used in repoling the specimen. For each measurement, the data were sampled at each second of the first 10s period. A data truncation method as reported by Wang et. al. was used. To eliminate any uncertainty due to the cycling-induced temperature, measurements were taken 1 h after the cycling had been paused. Results will be reported for two PZT stacks (No. 02 and 05) in this study. 

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