SH7055S Datasheet, PDF (897/1002 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family/SH7000 Series

Section 25 Reliability
25.1 Reliability
A failure rate curve represents an index of the reliability of a semiconductor device. The failure
rate curve traces a bathtub shape over the course of time, as is shown in figure 25.1. The curve is
divided into three periods according to the type of failure phenomena: an initial failure period, a
random failure period (functional lifetime), and a wear-out failure period. Initial failures, which
occur during the initial failure period, are caused by contamination with foreign matter and
localized chemical pollution; these can be eliminated by screening. Wear-out failures in the final
period are caused by the deterioration of materials that make up semiconductor devices during
long periods of usage. Random failures, which occur during the random failure period, are thought
to occur in cases where a device with a minor failure is not removed by screening, and so is
shipped, and then fails during the customer’s production process or in the field, and in cases where
a failure which should normally not have occurred until the wear-out period occurs earlier because
of variations in production. Therefore, the reliability of semiconductor device is secured by
appropriate screening to reduce the presence of initial failures and high reliability design to
prevent the occurrence of wear-out failures. The reliability of a product is confirmed by producing
a large quantity of prototypes for checking of the initial failure rate and executing accelerated life
testing to identify the wear-out failure time in a realistic environment.
Initial failure
period
Functional lifetime
Wear-out failure
period
Random failure period
Time
Figure 25.1 Failure Rate Curve (Bathtub Curve)
Rev. 2.0, 07/03, page 859 of 960