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Recent published data show the complete pattern of defect failures, intrinsic failures and the transition region between them. This explains many earlier misinterpretations. It provides a life curve for intrinsic failures, extending far beyond observation times in most cases, using a plot of acceleration factors independent of the 1/E vs. E relationship controversy between 6MV/cm. Life is linear with 1/E at 6MV/cm and above. Estimates of defect densities are available from the transition region, and are capable of extrapolation from high-E life tests to low gradients of operation. At voltage gradients much below 6MV/cm, however, this extrapolation cannot be corroborated in the long straight line of the transition. A single point test can be performed at about the time to the inflection point at 8 or 9 MV/cm stress to serve as a quality control point for the oxide defect density. This transition life line, however, can be used to derive a plot of failure rate which can be used to define screening procedures.

SUMMARY Accelerated humidity test data on plastic res are analysed, showing higher thermal acceleration and longer life for modem components compared to older ones. Accelerations for total test time in humidity are given, and the effect of assumed moisture ingress time through the plastic is also treated. A procedure for formal qualification of moisture life is proposed. obtain the estimate of 1m after the removal of freak failures'" from the distribution. The observed ratio, R o , of 1m (T/RH) to 1m (85/85) was then comparcd with the calculated ratio, Re , according to the for­ mula being investigated. The ratios were examined to obtain thc smallest standard deviations and the highest correlation coefficient between R o and Re . Since the same electrical bias conditions were held through each study, the ratios normalize the effects of test-ta-test variations in bias, device structure or contamination level. A common relationship was found to be optimum for stresses both higher and lower than the reference (85/85) from 158°C down to 50°C and from 100 per cent RH down to 50 per cent RH, the range of the available data. The formula has the form

A Duane plot is a straight line relating the log of cumulative failure rate (or of cumulative MTBF) to the log of cumulative equipment operating hours in a series of equipment tests. The straight line provides an easy translation from the cumulative line to a line of instantaneous failure rate (or to instantaneous MTFB). This technique has also been applied to the early failure rates of operating integrated circuits (ICs); the cumulative plot has the same usefulness in data smoothing, and the same relationship to instantaneous failure rate applies. The cumulative failure rate plot produces a curved line instead of a straight line. The Duane relationship applies at any time point, however, and depends only on the slope of the line at that time. For either application, the cumulative data should not be forced to fit a straight line; such forcing causes the early reliability history to be lost, and the latest history may be improperly determined from too few points. This is not just of historical interest; it concerns whether reliability is still improving usefully, or whether a point of limited return is being approached. An additional point of concern is indicated by the example of rapidly reducing failure rates in early life of semiconductor devices. For equipments using many of these devices, the Duane plot assumption of a constant failure rate during each equipment test period is probably not true.

This paper reviews all published life in humidity conditions vs life at 85C/85% RH for epoxy packages; 61 data points are used. An acceleration formula is described which provides direct extrapolation from test results in autoclave tests at up to at least 140C to low-humidity down to below 30XRH. This formula compares favorably with previously-published formulae. The possible effect of the Tg of the epoxy is recognized, and other high-temperature and low-humidity effects are disclosed. Recommendat ions are made for future tests, replacing 1000 hours at 85C/85%RH with a 20-hour test at 140C/100%RH, to reduce test time and increase test usefulness.