Multilayer Ceramic Capacitor Quality Related Microscopic Analysis

As an important chip component, more stringent requirements are put forward for Multi-layer Ceramic Capacitor (MLCC) in the area of miniaturization, high-capacity, high-voltage and high-frequency. The quality and reliability problems in the production and application are increasingly spread. It has become an urgent problem to strongly ensure and strengthen the quality and reliability of MLCC, which is regard as irreplaceable chip component in modern military weapons and aerospace systems. The present work focus on the issues research on the problems of the match of ceramic dielectric and silver paste, optimization of process, the factors affecting the quality and reliability, and failure analysis of production. The main work and the research results were summarized as follow.(1) To research shape-controlled silver chloride, the phenomenon that plenty of silver nanoparticles sprouted on the surface of silver chloride particles under electron beam irradiation and the formation mechanism were studied. The method to overcome the problem of morphology change was researched, which is helpful to obtain the actual analysis result.(2) On the quality and reliability problems during the sintering process of the ceramic dielectric, the formation mechanisms behind defects such as split, layering, poor continuity of inner electrode, layering in termination electrode-dielectric interface, holes, cracks, plating permeation of termination electrode were analyzed and summarized. The sintering temperature experiment of DP1187-type termination silver paste was conducted. Through comparing micro structure and composition distribution of the silver electrode surface, and silver-nickel interface bonding, the best sintering process which met the performance requirements was found.(3) Aiming at termination electrode permeation during plating process, the capacitors which frequently occurred plating permeation in production process were selected as experiment samples. Ni and Sn plating layer, silver layer, and ceramic dielectric were micro-analyzed and compared with the control samples. The formation mechanism of termination electrode permeation was discussed and recommendation for improvement was proposed. The experiment results suggested that the silver termination electrodes extended and spread from edges to middle on the surface of ceramic body in sintering process, which improved the conductivity of vicinity ceramic body of silver terminations. Then, higher conductivity facilitated absorption of plating metal on. the surface of ceramic body in plating process, which led to the plating permeation.(4) Micro-analysis of samples existing plating problems showed there were obvious huge Ag2S grains on the surface of silver electrode after sintering, resulting in the declining of thickness and discontinuity of Ni and Sn coating, poor Ag-Ni interface bonding and other issues. Combining with production process and investigation results, it suggests the S of silver termination electrode which cause coating problem came from the furnace wall. FeSx of furnace wall oxidized and decomposed, causing sulfur content of the sintering atmosphere rose, and leading to the formation of Ag2S. By cleaning the sintering furnace, Ag2S on the surface of silver termination electrode and the quality problems of coating disappeared.(5) The composition analysis, combining with the production process and performance test, was conducted to determine the source and forming causes of metal adhering on the surface of the MLCC ceramic body. The results suggested that metal was introduced by the friction between termination electrode and ceramic body during the late performance test and screening process, in which the products were stored in together. The issue was completely solved by taking appropriate measures.(6) Appearance inspection, the destructive physical analysis (DPA), electrical performance test and micro-analytical techniques for failure MLCC during application were conducted. The investigation result indicated that direct failure reason was dielectric thermal breakdown. The failure product was mechanically pressed during installation and formed micro-cracks, which caused leakage current increased, insulation resistance decreased, dielectric loss and heat rose during application, leading to thermal breakdown inside ceramic body eventually.Through above analysis work, the phenomenon and mechanism of morphology changing of silver chloride under electron beam irradiation was discussed. The technology improvement measures were applied in raw materials inspection, the process contrast and optimization of co-firing, termination electrode sintering and electroplating, pollution sources determine, quality evaluation, failure analysis and so on. That provides a route to improve the quality and reliability of MLCC, and a positive role to solve the product failure.