Method for estimating the life of multilayer ceramic capacitors

When electronic components are used in assembly into various types of electronic devices and are actually applied to the market, they need to face various external stress reactions. For example, physical strain caused by falling of an electronic device, thermal strain caused by a difference in temperature between cold and heat, electrical strain at the time of energization, and the like. With these external strains as an incentive, there are cases where electronic components fail when the product is used. Therefore, from the design stage of each electronic component, Murata studies the mechanism of external strain and failure, and feeds back to the reliability design of electronic components. At the same time, by grasping the relationship between the strength of external strain and the time and probability of failure, the "acceleration model of external strain and fault occurrence" is established to evaluate the durability of electronic components in a shorter test time. . As a specific case of the acceleration model, the temperature and voltage acceleration of the durability of the multilayer ceramic capacitor will be described. In general, a multilayer ceramic capacitor is composed of an electrical insulator (dielectric) and is highly reliable for continuous energization.

For example, a control module installed near an automobile engine will increase the temperature of the surrounding environment during use.

Figure 1 shows the internal state of the ceramic material used in the capacitor when it is energized in such a high temperature environment.

Atom-level charge defects with very little internal content in the ceramic material move from the + pole (positive electrode) to the - pole (negative electrode).

An electric ceramic represented by barium titanate, during the firing process, contains a very small number of atomic-level defects (called oxygen vacancies) inside the crystal structure, which can be slowly moved by an externally applied voltage and will accumulate in the near future. - Near the pole, the ceramic insulation may eventually be destroyed.

Thus, the durability years (lifetime) of the multilayer ceramic capacitor depends on the moving speed and amount of oxygen vacancies in the ceramic material, and the ambient temperature and the load voltage at the time of product use should be taken as parameters when establishing the model. In general, the acceleration model using the Arrhenius equation can be widely applied, but as a simple calculation method, the following empirical formula can also be used.

Through this relationship, accelerated tests are performed under more stringent conditions (higher temperatures, higher voltages) to estimate the number of years of durability of the product in actual use.

Here, let us try to compare the accelerated test of multilayer ceramic capacitors with the preset use environment of actual products. At this time, the endurance test time in the acceleration test of the capacitor is expressed as LA, and the equivalent number of years in the actual use environment is expressed as LN, and is used in the above formula.

In this way, the 1000h endurance test conducted at 85°C and 20V can be estimated, which is equivalent to 362039h (≒41 years!) at 65°C and 5V application environment. Although the voltage acceleration constant and the temperature acceleration constant used for calculation differ depending on the type and structure of the ceramic material, by using the acceleration model, it is possible to verify the number of years of durability in a long-term actual use environment based on the test results in a short period of time.

The above is an example of a multilayer ceramic capacitor, and there are various types of electronic components that are generally used and an intended use environment. Therefore, it is very important to establish a strain-dependent acceleration model that affects various electronic components.