Estimating parameter end points for combined environments [semiconductor devices]

The hardness assurance problem of estimating electrical parameter end points in a combined environment (e.g., neutrons and total ionizing dose) using data in each environment separately is solved. The methodology applies to any other situation where several independent normally distributed variables combine to form a final parameter. The precision deteriorates only when the estimate of end points would be questionable in any event, namely, when very high confidence and probability are required but too few parts were sampled for the environment which is the major source of variation