Use Condition Risk Assessment for Moisture Related Failures

This study focuses on the understanding of moisture diffusion physics under use conditions (UC) and its impact on definition of qualification requirements. It uses computational modeling and detailed measurements of UC to challenge some long held assumptions used in moisture risk assessments. It introduces the quantity called "Stable Wetness" to account for moisture amount present in the package under UC, and couples it with Peck's empirical function to define the accelerated test duration (the qualification requirement). It concludes that due to the competing mechanisms of moisture and temperature there exist a "critical user", given in terms of ON-time per day that maximizes the requirements. It is this user that determines the qualification requirements, as opposed to, commonly assumed, the longest OFF-time user. The study also provides a simple equation for the computation of Stable Wetness, thus enabling an easy application of the proposed concepts in practical applications.