-Time-to-failure distributions have been derived based on run hours of the system between two consecutive failures. The Weibull distributions are widely used by reliability practitioners to estimate the product time-to-failure. Manufacturing companies usually generate the reliability report in a quarterly basis (i.e. 13 weeks). Using the data in Fig. 9, we estimate the system time-to-failure by fitting the Weibull distribution and the results are summarized in Table 2. To estimate the time between failures, the system is assumed to operate 24 h a day and 7 days a week. This is a typical operating profile in the semiconductor testing industry, and the time-to-repair is relatively small and negligible. From the table, it shows the system reliability is growing as the mean lifetime in the Q4 reaches 1,825 h. Also notice that the mean lifetime in Q1 is higher than Q2 and Q3. This is understandable because the life failure rate in Q1 is smaller as shown in Fig. 9.