Study Of Metallization Of Electronic Ceramics

Electronic ceramics, the foundation of electronic components, are widely used in the field of electronic information. China is a large producer of electronic ceramic devices, with two-third of the global production. The metallization on the surface is a critical process during electronic ceramics manufacturing, which directly affects the electrical properties, reliability and welding performance of the ceramics. So far, mainstream electrode metallization process still use screen printing, electroplating and other traditional technology, which has not only high cost and poor reliability, but also high energy consumption and serious pollution. With the full implementation of ROSH standards, lead-free green technology has become the inevitable development trend of electronic products manufacturing. It is imperative to adopt the green technology to replace screen printing to realize metallization, and to improve the quality of the electronic device.This paper choses ZnO-based ceramics and thermistor ceramics as the main research object to study the sputtering metallization of electronic ceramics. We analyzes the influence of the sputtering parameters, coating materials and structure on the properties of electro-ceramics. We put forward the optimal film structure, and have successfully applied this technology to realize metallization in many companies. The main work and research results of this paper are as follows:1. Sputtering metallization of zinc oxide varistors is a major technical problem that has not been solved at present. We have analyzed the adhesion mechanism, conduct mechanism and welding mechanism between the electrode and ceramic, systematically studied the impacts of the sputtering process, the electrode materials and microstructure upon the performance of ceramics. Combined with the requirement of metallization, we put forward the optimum multilayer film electrodes and design principles, successfully applied to industrial production. Results show that the tensile strength of NiCr/Cu/Ag electrode is up to 13.9MPa. The change ratio of nonlinear voltages at an environment of 125℃ after 100 hours was chosen as the main reliability parameter. Results indicate that the sputtered electrodes could improve the reliability of varistors by reducing the change ratio from 1.32% to 0.61%, with the main technical parameters, for example nonlinear coefficient, varistor voltage and leakage current, exceeding the screen printing electrodes. However, the former electrode thickness is only 1/4 of the latter, the cost of production is reduced by 50-60%.2. To low curie point PTC ceramics, it is difficult to use screen printing and the conventional sputtering process to form electrodes. We choose NiCr, Al respectively as transition layer and barrier layer, which can effectively prevent the diffusion of copper or silver ions to the ceramic body, successfully solved the problem of low Curie point PTC thermal ceramics metallization.3. Using base metal materials as electrode is inevitable trend for the metallization. In the paper we first successfully studied Al/Cu and NiCr/Cu electrodes. Large scale industrial production shows that the welding ability, energy absorption capacities, tensile strength and other technical parameters of the new electrodes can all meet the requirements, while the costs are greatly decreased. This technology will have good market prospects.4. NTC thermistor metallization process has been very difficult to achieve good adhesion, which have limited the application of sputtering technique in NTC. We studied and analyzed the microstructure of NTC thermistor, considered that the screen printing process is equivalent to second sintering, which can effectively change the grain size and influence the bonding strength between the deposited electrode and the substrate. This discovery challenges the traditional reviews of "Screen printing process does not affect the crystal structure of NTC", which provides a theoretical guide for NTC sputtering metallization.