Rintaro Minamitani

A field life prediction model of electronic modules corroded by S8 gas released from rubber ducts in-vehicle engine rooms

ABSTRACT A model which predict the field life of electronic modules corroded by S8 gas in vehicle engine rooms is constructed. The in-vehicle module field life is predicted from the accelerated test results of module alone and the measured results of in-vehicle module field environment conditions. In the modules, a circuit substrate with Ag wiring is placed on a baseplate within a housing and sealed with silicone. The S8 gas is produced by the release of the free sulphur of rubber ducts in engine room at the maximum temperature holding time after engine stop. This S8 gas permeates the silicone seal and corrodes the Ag wiring. The ratio of the corroded part thickness to the initial thickness of the Ag wiring increases with the increase of the number of engine start/stop cycles. The calculated results coincide well with the observed results of the corrosion thickness in an actual vehicle.

Antifreeze-Permeation Behavior in a Small-Size Liquid Cooling System

To ensure reliable operation and high performance of small-size liquid cooling systems, it is essential to evaluate the liquid-permeation behavior of polymer and to optimize the liquid weight in the system. Accordingly, the present study quantifies the liquid-permeation behavior of an isobutylene-isoprene rubber (IIR) tube and a nickel-plated syndiotactic polystyrene (SPS) plate in antifreeze, namely, a water-propyleneglycol solution. It was found that the IIR tube is permeable to only water in the antifreeze, not to propyleneglycol, because the water vapor pressure is 340 times higher than the propyleneglycol vapor pressure. Moreover, the nickel plated SPS plate has negligible low liquid-permeability, because the liquid barrier produced by the nickel plating is 10 times better than that by the non-plated SPS plate. Accordingly, after long-term operation of the small-size liquid cooling system, the above-mentioned selective water permeation in antifreeze leads to degradation of cooling performance. This is because the viscosity of the antifreeze and pressure losses in the cooling path increase as a result of the increased antifreeze concentration. These liquid-permeations and concentration changes of antifreeze must therefore be taken into consideration when specifying the required liquid weight in the liquid cooling system.

Corrosion Behavior of Copper in Liquid Perfluorocarbon.

Liquid perfluorocarbon coolant Fluorinert® FC-72 for electronic devices has high thermal stability and low chemical reactivity. However, the presence of water in FC-72 at less than 10wt ppm has been shown to appreciably increase copper corrosion. In the present study, the corrosion mechanism under low solubility of water in FC-72 was investigated by chemical analysis, water volume measurement, and corrosion testing. It was found that FC-72 liberates no decomposition products in temperatures below 100°C and copper corrosion depends on liquid temperature, dissolved water, and oxygen. In FC-72, copper specimens were corroded by wet oxidation at temperatures of 50, 70, and 85°C and by both wet and dry oxidation at 100°C. Copper corrosion was induced when dissolved water in FC-72 was increased to more than 8wt ppm. However it was reduced when oxygen in FC-72 was decreased to less than 25ml/L. Dissolved water in FC-72, as in air, equilibrates with adsorped water on copper surface. Therefore, the mechanism of copper corrosion in FC-72 is the same as that in air. It is considered that the mechanism for FC-72 can be extended to explain corrosion behavior in almost all inert coolants.