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- LTCC (14)
- Sintering (5)
- Glass ceramic composites (4)
- Inclusions (4)
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- Sintering kinetics (3)
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- Coefficient of thermal expansion (CTE) (2)
- Coefficient of thermal expansion CTE (2)
- Crystallization (2)
Eingeladener Vortrag
- nein (13)
Defekte und störende Oberflächenstrukturen keramischer Bauelemente, die aus keramischen Folien gefertigt werden, haben neben keramtechnologischen Prozessfehlern vielfach ihre Ursachen in dynamischen Prozessen bei der Trocknung der Nassschichten. Neben Einzeldefekten wie Poren oder Rissen können in Grünfolien während der Trocknung auch oberflächenspannungsinduzierte periodische Schichtdickenunterschiede auftreten. Grenzflächenendynamische Bewegungen wie auch die Bildung von Blasen oder Agglomeraten treten gleichermaßen in gegossenen keramischen Schichten und in keramikfreien Polyvinylbutyral/Weichmacher-Schichten auf. Das analoge Verhalten der untersuchten gegossenen keramischen Schichten und der entsprechenden keramikfreien Polymerschichten bezüglich der Entstehung dieser Oberflächenfehler sowie Möglichkeiten zur Fehlerreduzierung werden aufgezeigt.
Neue niedrig sinternde Mikrowellenkeramik für Anwendungen in der mobilen Kommunikationstechnik
(2003)
An Proben aus der Produktion wurde die Abhängigkeit der Emission vom Zeitpunkt der Probenahme, die Korrelation zu bestehenden Prüfverfahren durch Extraktion und der Einfluss des Klimas untersucht. Es zeigt sich, dass die Luftfeuchtigkeit einen großen Einfluss uf die Formaldelhyd-Emission hat. Ein Prüfverfahren zur Bestimmung der Ausgleichskonzentration von Formaldehyd wird vorgeschlagen.
LTCC-modules with integrated ferrite layers - Strategies for material development and co-sintering
(2008)
Green compacts of ceramics, glass ceramic composites and sinter glass ceramics contain
different amounts of organic materials added as pressing aids or binders. Before sintering, these
organics have to burn out completely. In oxidising atmospheres, the debindering process is mostly
exothermic and therefore difficult to control. This uncontrolled heat production due to locally enhanced
debindering and respective gas release may cause damages in the green compact microstructure.
Therefore, debindering is usually operated with very low heating rates (< 3 K/min) which requires
long processing times of many hours. In this paper, we will show that it is possible to reduce
the processing time for debindering dramatically by using the decomposition rate of the organic
binder, detected by the weight loss of the sample, as a control factor of the furnace.
New applications of low-temperature co-fired ceramics (LTCC), such as pressure sensors or integrated functional layers, require materials that possess higher coefficients of thermal expansion (CTE). To fabricate LTCC with elevated CTE, two methods of material design are examined: firstly, glass ceramic composites (GCC), which consist of >50 vol% glass in the starting powder, and, secondly, glass-bonded ceramics (GBC), where glass is added as a sintering aid only. The CTE of GBC is mainly determined by the crystalline component. For GCC, the CTE can be well predicted, if CTE and elastic data of each phase in the microstructure are known. A nonlinear characteristic of the CTE versus phase composition was found with increasing Ecrystals/Eglass ratio and absolute CTE difference between the components. The glass composition and glass amount can be used to compensate the fixed properties of a crystalline material in a desired way. However, because the CTE and permittivity of a glass cannot be chosen independently, an optimum glass composition has to be found. For a given LTCC, it is possible to control the devitrification by shifting the glass composition. In this way, the resulting CTE values can be predicted more exactly and tailoring becomes possible. Different LTCC materials, based on the crystalline compounds Ba(La,Nd)2Ti4O12, ZrO2 (Y-TZP), SiO2 (quartz), and specially developed glasses, possessing an elevated CTE of around 10 × 10-6 K-1 while showing permittivity εr between 6 and 63, are introduced.
LTCC-Keramik im Automobil
(2003)
We studied sintering of LTCC-type glass matrix composites (GMCs) consisting of small glass and alumina particles of equal size. Primarily, crystals act as rigid inclusions, decelerating the densification rate. In later stages, they also dissolve, partially increasing the viscosity. Release of alumina finally induces crystallization of alumosilicates, which enables post-firing stability. To study both effects, two model GMCs were prepared: an α-Al2O3 + barium alumoborosilicate glass (BABS)GMC, which shows neither significant dissolution nor crystallization, and an α-Al2O3 + calcium alumoborosilicate glass (CABS)GMC, which dissolves readily and promotes crystallization. The kinetics of shrinkage for both GMC were modeled by utilizing Frenkel theory for the early stage and MackenzieShuttleworth theory for the late stage, assuming that sintering is superimposed by the weighted contributions of triparticle glasscrystal clusters, their random occurrence (ideal mixing), and a shrinkage rate controlled by the GMC effective viscosity. In agreement with modeling, the experimental results showed that the shrinkage rate of BABSGMC decreases progressively for crystal volume fractions Φ > 0.15. The attainable shrinkage is reduced by up to 8% for Φ = 0.45. For the CABSGMC with Φ = 0.25, a reduction of Φ to 0.20 was evident due to partial α-Al2O3 dissolution. This effect was found able to increase the sintering temperature by ~5060 K.
LTCC-Modules with integrated ferrite layers - Strategies for material development and co-sintering
(2009)
The integration of passive components (resistors, capacitors, inductors) into LTCC modules is a challenging task in multilayer ceramics technology. We report on multilayer assemblies consisting of combined layers of ferrite and dielectric LTCC tapes. Ni-Cu-Zn ferrites with maximum shrinkage at 900°C were processed to green tapes and laminated with dielectric LTCC tapes. Cosintering at 900°C led to multilayers with different defects such as incomplete densification of the ferrite layers, cracks, and warpage. Since ferrite tapes do not really allow compositional changes without deterioration of magnetic properties, the dielectric tape was modified with the following objectives: (i) matching of the shrinkage curves of dielectric and ferrite materials, (ii) adjusting the coefficients of thermal expansion to avoid cracking during cooling, and (iii) controlling of interface reactions. Using this concept we fabricated dense and defect-free multilayers consisting of dielectric and ferrite layers. However, compositional changes of the individual ferrite tapes require the development of a specific dielectric tape material with tailored properties.
Über das Sintern von LTCC
(2007)
Multilayer ceramic devices based on low-temperature co-fired ceramics (LTCC) materials provide a very promising technology. Most LTCC tapes available today contain considerable fractions of glass powders to lower the sintering temperature. However, the glassy phases offer more possibilities to set a proper sintering behavior, on the one hand, and to tailor the desired properties of the final LTCC substrate, on the other. The exploitation of demixing and subsequent crystallizing glass compositions was shown on an example of a low-permittivity (4.4)low-loss (1.5 × 103) LTCC with a high quartz content. In another LTCC material, undesired demixing could be restricted and the crystal phase anorthite could be triggered by partial dissolution of alumina in the liquid phase during sintering. To estimate the effect of silver diffusion in the latter material, the surroundings of a pure silver via were studied. A silver-contaminated range of 50 µm was detected. Using model glasses containing silver oxide, a strong influence of dissolved silver on viscosity and crystallization behavior of the liquid phase was demonstrated. The dielectric properties of the sintered substrates were not degraded.
Über das Sintern von LTCC
(2007)