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Suppression of Silver Diffusion in Low Temperature Co-fired Ceramic by Copper Oxide Addition
Keywords: LTCC, Sliver diffusion, Dielectric property
Silver is widely used as the electrode material in Low temperature co-fired ceramic (LTCC) components and modules manufacturing. However, some undesirable compatibility problems including silver diffusion and cofiring defects like delamination, cracks and camber, might occur during cofiring of LTCC materials with silver electrode. Silver diffusion is one primary problem because it could lead to leakage current increase and degradation of the electrical properties and reliability of the LTCC modules. So much work has been carried out to explore the intrinsic mechanism of sliver diffusion in LTCC materials. [1-3] It was reported that interfacial reactions between silver and the glass matrix could change the microstructure of LTCC materials and plays a key role in sliver diffusion. [2] The silver diffusion was also considered to be related with the viscous flow of glassy phase during cofiring. [4] Efforts have been therefore made to increase the viscosity of glass phase by adjusting the composition of LTCC materials. [5] While, due to the variety and complexity of the LTCC material system, the cofiring compatibility between silver electrodes and LTCC materials still a key trouble maker in LTCC material and components development. In this work, a series of CaO-Al2O3-B2O3-SiO2 glasses fine powders were prepared by high temperature melting and a two-step milling. Low temperature cofiring ceramics (LTCC) were developed by mixing the boroaluminosilicate glasses with Al2O3. The cofiring compatibility of the LTCC materials with commercial sliver paste was investigated. The experimental results indicated that the diffusion of silver conductor in the LTCC green tape composed of boroaluminosilicate glasses and Al2O3 during sintering could be suppressed by the addition of 1 wt% copper oxide. Thermal dynamic analysis indicated the diffusion coefficient of silver in the LTCC samples was largely reduced by copper oxide addition. Sliver was found dispersed in glass phase in fired LTCC material without copper oxide addition by transmission electron microscopy (TEM) observation. X-ray diffraction and TEM analysis suggested that copper oxide addition promoted the crystallization of borosilicate glass. The quick increase in the glass viscosity resulted by the crystallization of glass matrix should be the main reason that retarded the silver diffusion in LTCC ceramics.
Zhifu Liu,
Shanghai Institute of Ceramics, Chinese Academy of Sciences
Shanghai, Shanghai

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