Comparison of High-Resolution Patterning Technologies for LTCC Microwave Circuits

Abstract

Low-temperature co-fired ceramic (LTCC) are widely acknowledged for wide-band and microwave circuits. Within the project consortium KERAMIS, implementation of higher functionality in LTCC substrates is being investigated. Among the applications considered are a 4 × 4 switch matrix [1], voltage-controlled oscillators [2], and amplifiers for multimedia satellite communications working in Ka-band. In order to add more functionality (e.g., filters, couplers) in LTCC, current patterning limits of line width and line separation need to be extended. Four different technologies were considered for higher resolution: a) fine-line printing technology with special screens, b) photo-imageable pastes, c) etching of thick-film conductors (co- and post-fired), and d) thin films on LTCC. Evaluation of patterning technologies is based on a test coupon that was designed and manufactured by the consortium members. The artwork contains lines, line transitions, ring resonators (microstrip and stripline), edge-coupled filters, DC blocking structures, and various lines for DC resistance testing. The smallest gap definition is 50 μm. Two substrate materials, Du Pont tapes 951 and 943, are included in the study. In addition to the main frequency band of interest in the project (17–22 GHz), these structures have been characterized up to 50 GHz. Electrical results are correlated to physical measurements of the structures (line width, spaces, and tolerances) and are evaluated with respect to performance, manufacturability, and yield. Results show excellent performance for screen-printed structures and demonstrated the importance of mask tuning to achieve optimum resolution (under etching etc.).

Fine-line structuring of microwave components on LTCC substrates

“…The line resolution after process optimization reaches about 10 /lm. Excellent geometrical tolerances can be obtained with chromium masks [7].…”

“…To meet the conditions for more accurate structural resolution, the sintered thick-film pastes can alternatively be etched, as presented in [6,7]. Another way to fabricate fme-line structures with a resolution down to 30 /lm for lines and spaces using screen printing techniques takes advantage of photo-imageable pastes such as the Fodel® system [4,8].…”

High‐resolution patterning on LTCC by transfer of photolithography‐based metallic microstructures

“…These include photo‐imageable pastes, etching of thick film paste on LTCC and laser structuring. These techniques enabled structure resolutions in sub‐10 μm range, which is well below the standard screen printing resolution 8–11 …”

“…These techniques enabled structure resolutions in sub-10 µm range, which is well below the standard screen printing resolution. [8][9][10][11] This paper describes a technique of transfer technology for realizing high-resolution microstructures on LTCC. Previously, US patents have described methods for producing high-density, fine circuit pattern printed circuit boards using such transfer technology.…”

Magnetron Sputtered AlN Layers on LTCC Multilayer and Silicon Substrates

“…The monolithic integration of functional units on the package contributes to cost reduction and system miniaturization. It requires the direct deposition of functional thin film components on LTCC ceramics [27].…”