In Chapter 1, we explained the basic concept of reliability and failure and various reliability test methods actually used in engineering. From here, we will discuss accelerated tests performed to estimate the service life of electronic components, using the example of multilayer ceramic capacitors.
Electronic components are built into many different kinds of electronic devices. When actually used in the market, they are exposed to all types of external stress. For example, there is the physical stress of the electronic device being dropped, the thermal stress of temperature differences and the electrical stress applied when the device is powered up. These types of external stress become factors that may cause failure of electronic components during use of the product in which they are embedded. To address this, we investigate the mechanisms of external stress and failure occurrence in each type of electronic component from the design stage and use the results as feedback for reliability design of electronic components. Moreover, by assessing the relationship between the degree of external stress and the onset and probability of failure occurrence, we can build an "external stress and failure occurrence acceleration model" that lets us assess service life of electronic components more quickly.
To give a specific example of an acceleration model, I will talk about temperature and voltage acceleration aspects of service life in multilayer ceramic capacitors. In general, multilayer ceramic capacitors are made of an electrical insulator (dielectric) and are known to be extremely highly reliable even when continuously energized.
For example, the ambient temperature around the control module installed near the automobile engine room becomes very hot during use.
Figure 1 shows what happens inside ceramic material used in capacitors when energized under a high-temperature environment.
The atomic level electrical defects contained in minute quantities in ceramic material are thought to move from the anode (+) to the cathode (-).
Figure 1.(The figure is spread when you click.)
In barium titanate and other electric ceramics, a minute number of atomic level defects (called oxygen defects) are encapsulated in the crystal structure during the firing process. They gradually shift when voltage is applied externally and eventually accumulate in the vicinity of the cathode, at some point leading to breakdown of the ceramics.