The study dielectric measurement and sintering match of LTCC

• Main Authors: Jui-Yu Jao, 饒瑞榆
• Other Authors: Pang Lin
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/67062624958887796037

博士 === 國立交通大學 === 材料科學與工程系所 === 95 === The sintering behavior of low temperature co-fired ceramic (LTCC) is a key to decide the device characteristics. The way to evaluate the electronic characteristics after sintering, and what kind of material composition has better sintering match are the major topics in this paper. This thesis is composed of three parts. In the first one, a method of estimating the dielectric constant (ε) of dielectric layers in LTCC devices was developed. A band-pass filter (BPF) circuit was designed such that its second harmonic frequency (SHF) strongly depended on the ε of the relevant capacitor built in the BPF. The ε–SHF correlation was established by model simulation. The design of the BPF was realized with various dielectric layers, and the measured SHF was used to determine the ε values of the capacitors from the ε–SHF relationship. These ε values were found to be consistent with those of the sintered pellets, prepared with the same dielectrics and process as BPFs. The ε values of the dielectric layers in other LTCC devices were estimated by this method, in which the BPFs made of the same dielectric layers were fired as dummy samples along with the devices. The second part, a new technique developed for the low shrinkage of LTCC is proposed; this technique is based on a self-constraining mechanism, which relies on composite green tapes formed by two laminated glass layers, each of which has a distinct softening point (onset shrinkage temperature, OST) and a crystallization temperature (CRT). Each layer works as a constraining layer for the other layer in a distinct temperature range to prevent excessive linear shrinkage along the layer plane. The OSTs ranging from 802 to 606oC are adjusted by controlling the amount of Na2O (0~1.0 wt%) added to the CaO-SiO2 glass. The OST and CRT of the two glass layers as well as the heating profile have strong effects on shrinkage ratio, the lowest of which is found to be only 0.2% after sintering up to 880oC. The measured dielectric constant of the sintered samples is approximately 6.0 within a narrow variation range even when the samples have a wide range of shrinkage ratios. The last one, inductors using a new LTCC design, that Ni-Cu-Zn ferrite was buried in B2O3-SiO2 glass within the core of spiral silver coil, were fabricated. The inductance and quality factor of inductor with embedded ferrite are larger than that of pure B2O3-SiO2 glass. Ni-Cu-Zn ferrite was incompatible with the B2O3-Si02 glass during the co-firing process due to sintering shrinkage mismatch. The incompatibility was resolved when 35wt% Al2O3 was added into B2O3-SiO2 glass, which produces glass-ceramic, and 2wt% of Bi2O3 was fluxed into the Ni-Cu-Zn ferrite as sintering aid. Addition of 2wt% of Bi2O3 not only enhances the densification, but also increases the permeability of Ni-Cu-Zn ferrite.