Study On The Glass Package And The Silver Paste Of Terminal Electrode Applied On The Laminated PTCR

In order to meet the need to the development of SMT technology, miniaturization, lowresistance and lamination have become the development trend of the positive temperaturecoefficient resistance. Laminated chip-type thermistor is a complicate structure resistancealternately stacked with ceramics and Ni electrodes. As a complete laminated PTCR, everyend face of the co-firing ceramics should be covered with three terminal electrode layers,the silver electrode, the Ni layer and the Sn layer. The electroplating process that used toform the Ni layer and the Sn layer can easily lead to the diffusion of metal ions in thesurface of the ceramic body to form a metal coating and cause a short circuit, as well as theacidic electroplating solution intrude into the ceramic body, leading to performancedeterioration. The glass encapsulation can protect the ceramics and the inner electrode. Thesilver electrode connects the inner electrode and the external electrode, Its electricalproperties is directly related to the performance of the PTCR. In this thesis, themanufacturing process of the samples were introduced and the room temperature resistanceand the Resistance-Temperature properties were tested. The glass package and the Agconductive paste that are suitable to the laminated PTCR were studied in this paper.Lithium potassium mixed water glass solution is used as glass package materials. It isone kind of low-cost, environmentally friendly package material that can be easily coatedand lead-free. Its film-forming properties, the sintering process, and the anti-voltageproperties were studied. The results show that when the water glass is sintered at atemperature of600°C with heating rate less than150°C/h, insulating one hour can form afilm without crack and crystallization. When the rate of the Li/K atoms is close to1, thefilm can get the higher withstand voltage value. The high modulus water glass has higherwithstand voltage value than the low modulus water glass.The Ag conductive paste is a complex composite system contains Ag powder, organicbinder, lead-free glass powder and so on.The Ni internal electrode cannot be dissolved inthe Ag paste, therefore, Ni₂B powder is added to enhance the solid solubility and oxidation.The experiments show that when the mass fraction of Ni₂B is about23%，the laminated PTCR achieved the most efficient electrical connection. The sintering temperature and thehold time were systematic studied, The Ag conductive paste that heating up to600℃usingthe heating rate of300℃/h and holding15minutes can get the best result.