Prakt. Met. Sonderband 46 (2014) 169
'e for various EFFECT OF RESIDUAL STRESSES ON THE STRENGTH OF
ot below the GLASS-CERAMIC MULTILAYER COMPOSITES COMBINING
served frend DIFFERENT MICROSTRUCTURES
R. Bermejo*, C. Krautgasser***, M. Deluca***, S. Strobl***, |. Kraleva***
I. Petschenig®**, F. Aldrian***, P. Supancic***, R. Danzer***
"Institut fir Struktur- und Funktionskeramik, Montanuniversitét Leoben, Leoben, Austria
bar-shaped - Materials Center Leoben Forschung GmbH, Leoben, Austria
he uncoated TDK-EPC, Deutschlandsberg, Austria
step for the
sion kinetics.
nical oxygen
nagnitude at ABSTRACT
2action. This
epth profiles Glass-ceramic composite materials such as Low Temperature Co-fired Ceramics (LTCC)
mperatures. are widely used as substrates in the production of electronic circuits for automotive and
yetween 500 communication devices. Microstructural features such as glass phase content, ceramic
n layer was particle size, shape and distribution, etc. can affect the fracture resistance of the material.
In addition, the strength is associated with the type, size and shape of the critical defect
(commonly a surface flaw) in the material. In this work, the strength distribution of different
LTCC systems was determined using a biaxial strength testing method (the Ball-on-three-
balls), comparing bulk substrates with multilayer architectures combining two different bulk
LTCC materials. An increase in strength was obtained in the multilayer composites
"ds and AVL (compared to bulk substrates), which was related to the compressive stresses in the
rgien 2020). surface layers generated during sintering due to the different thermal expansion
uthors thank coefficients of the layers. The magnitude of the residual stresses in the surface layers
t Leoben) for measured with Raman spectroscopy was in agreement with the difference in strength.
1. INTRODUCTION
Kharton Low Temperature Co-fired Ceramics (LTCC) consist of ceramic grains embedded in a
glass matrix. Due to the glass content, low sintering temperatures (i.e. below 900 °C) can
be achieved allowing a vitrification of the glass ceramic composite material [1]. This makes
the sintering of the LTCC tapes together with good conducting metals like silver, gold or
em. Phys., silver-palladium-alloys feasible. Laminates of LTCC tapes with internal 3D metal structures
can be utilized as functional components and used as ceramic circuit boards, for instance
01, p.1777. in mobile phones or as WLAN-, Bluetooth-, or RADAR-antennas, as well as in biomedical
sensors and devices . The LTCC-technology provides components with improved thermal
a TA. and geometrical stability compared to the widely used polymer based PCB (printed circuit
board)-technology. Due to their properties, ceramic circuit boards are often used in harsh
environments (e.g. elevated temperature, mechanical loading, vibrations). The structural
integrity of LTCCs is related to their mechanical strength and resistance to crack
propagation. Microstructural features such as glass phase content, ceramic particle size,
shape and distribution, affect the fracture resistance of the material. Due to the brittle
behaviour of glass-ceramic based materials, the strength (usually defined as a probability
function following a Weibull distribution) is related to the type, size and shape of the critical
defects (commonly surface flaws) in the material. A strategy to increase the strength is
