Large Thermal Expansion LTCC System for Cofiring with Integrated Functional Ceramics Layers.

Beate Capraro,Manuel Heidenreich,Jörg Töpfer

doi:10.3390/ma15020564

Abstract

We have studied the sintering behavior of CT708 LTCC tapes with large CTE of 10.6 ppm/K. This low-k dielectric LTCC material is a quartz-based glass ceramic composite system with partial crystallization of celsian upon firing. The shrinkage, densification and dielectric properties were examined using different heating rates and a sintering temperature of 900 °C. The maximum shrinkage rate is at 836 °C (for a heating rate of 2 K/min) with a sintering density of 95% and a permittivity of ε’ = 5.9 and tan δ = 0.0004 (at 1 GHz). Due to their similar shrinkage and thermal expansion properties, CT708 tapes may be cofired with functional ceramic layers. As an example, we report on cofiring of a multilayer laminate of CT708 and a Sc-substituted hexagonal ferrite for applications as integrated microwave circulator components. This demonstrates the feasibility of cofiring of functional ceramic tapes and tailored LTCC tapes and documents the potential for the realization of complex LTCC multilayer architectures.

Highlights

Low temperature co-fired ceramics (LTCC) is a ceramic substrate technology widely used in microelectronic packaging for the fabrication of 3D multilayer electronic substrates, RF circuits, or MEMS systems [1,2]
Preliminary tests with larger forces of F = 0.05 N or F = 0.1 N resulted in significantly larger total shrinkage. This is a typical signature of glass ceramics composite LTCC material which is compacted upon heating under load
This study reports on the sintering behavior, phase composition and properties of CT708 LTCC tapes

Summary

Introduction

Low temperature co-fired ceramics (LTCC) is a ceramic substrate technology widely used in microelectronic packaging for the fabrication of 3D multilayer electronic substrates, RF circuits, or MEMS systems [1,2]. It allows for miniaturization of complex electronic circuits or microsystems, and enables operation under harsh environments; e.g., increased operating temperatures. LTCC tapes are designed to have low sintering temperatures which allow cofiring with Ag conductor patterns at T ≤ 900 ◦C [1,2].

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