Methods of measurement of LTCC metallization thickness
Metallization provides electrical routing and serves as thermal via in LTCC (Low Temperature Cofired Ceramic) technology. High electrical and thermal conductivity is desirable. It is often achieved with the use of low electrical resistance materials, such as gold, silver and copper. The conductive paste made of these materials is expensive. Hence, the fabrication of LTCC has to be performance-wise and cost effective. The width, length and thickness of metallization are associated with the amount of conductor paste used. The thickness of metallization governs the functionality and performance of some components, such as resistor. In this paper, the physical attributes of LTCC substrate and its metallization was studied. Due to the constraint brought by the physical attributes of LTCC samples, various methods had been carried out. This paper also summarized the pros and cons of each method. The methods are limited to the equipment available.
Curvature evolution in LTCC tapes and laminates
Low temperature cofired ceramic (LTCC) substrates provide a low-cost packaging approach for radio frequency (RF) integrated circuits. Thermally-driven curvature development in these LTCC tapes and laminates, which can introduce property-limiting defects into a device, was examined quantitatively using an optical profilometer. Contrary to the standard perception of tape cast products, these specimens consistently experienced the largest increases in curvature during burnout rather than during sintering. Sintering actually leads to dramatic decreases in curvature. Slight anisotropic changes in curvature were observed when comparing those directions parallel and perpendicular to the tape casting direction. In the laminates, individual layer orientations had strong effects on overall curvature. Springback after the application of lamination pressure strongly contributes to curvature. "Microslumping" at the ends of the tapes/laminates occurred during sintering and could be accounted for via discrete element models of sintering. The latter phenomenon can be eliminated by controlling relative tape orientation.
An explicit knowledge-embedded space mapping technique and its application to optimization of LTCC RF passive circuits
A novel explicit knowledge embedded space mapping (SM) optimization technique is presented in this paper. It generalizes the implementation procedure of the efficient SM technique by introducing a buffer space called embedded knowledge space between the original coarse model space and the fine model space, where the ingredients of the coarse model space can be completely different from those of the fine model space. Therefore, this generic scheme can be used to map the coarse model space of arbitrary physical content to the fine model space of different physical content through the embedded knowledge space that is built up with the available radio frequency (RF) circuit CAD formula. The emphasis of the application of the proposed scheme is put on the design of low temperature cofired ceramic (LTCC) RF passive circuits in this paper, along with the required CAD formulas (knowledge) for typical embedded multilayer passives. The effectiveness of the proposed new scheme is demonstrated through two design examples of LTCC lumped element band pass filters for wireless applications. The detailed procedure and flowchart of the proposed implementation scheme are also given in the paper.