The Effects of Environmental Stresses on the Reliability of Flexible and Standard Termination Multilayer Ceramic Capacitors
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Flexible termination capacitors were designed to reduce stresses transmitted to the ceramic dielectric of a capacitor and thereby prevent flex cracking. Two studies were conducted to examine the reliability of flexible termination multilayer ceramic capacitors (MLCCs) subjected to environmental stresses. The first study used temperature-humidity-bias to compare the effects of termination type (standard vs. flexible), presence of a conformal coating (acrylic coating vs. no coating), and voltage bias level. In situ monitoring demonstrated similar failure statistics between the flexible and standard termination capacitors, presence of conformal coating, and voltage bias level. Upon removal from THB conditions recovery occurred only in the standard termination MLCCs. Flexible termination capacitors at the rated voltage bias were found to have more permanent failures after exposure to THB testing as compared to standard termination capacitors. Failure analysis indicated that silver and palladium migration between electrodes was the failure mechanism in the biased flexible termination capacitors.
In the second study flexible and standard termination MLCCs experienced a storage test in which they were exposed to elevated temperature and humidity conditions. It was found that the standard termination MLCCs had a lower reliability with the majority of the MLCCs failing compared to the flexible termination MLCCs where only one MLCC failed. Nearly all failures were for insulation resistance with few capacitors failing for other parameters. Subsequent bake-out of the MLCCs showed some recovery, however more failures were still occurring in the standard termination MLCCs compared to the flexible termination MLCCs. X-ray photoelectron spectroscopy and cross-sectioning were used to examine the failure mechanisms of the capacitors. A bulk migration of silver into the dielectric was determined to be one of the failure mechanisms in the capacitors.