Multilayer Ceramic Technology
Concept of Multilayer Ceramics TechnologyThe current trend of miniaturization in the electronics and communication sectors is on the rise, creating demands for packaging solutions with increasingly complex requirements. Since possibilities for reducing the size of conventional glass-to-metal seals have been nearly exhausted, it has become necessary to develop new and innovative approaches.
Ceramic-to-metal sealing represents one such approach, and it has the potential for further development. In these seals, various types of electrical feedthroughs are embedded into a special ceramic material, offering totally new possibilities in the encapsulation of complex electronic and optoelectronic systems.
Driving factors for innovative packaging solutions with ceramic multilayer feedthroughs are:
- Cost savings
- HF applications
Multilayer Ceramics ManufactureMultilayer ceramics are manufactured using high and low-temperature, co-fired aluminium oxide ceramics. The ceramics are produced by mixing ceramic and glass powders of specific composition, and small quantities of binding agent and solvent to create a homogeneous slurry. This slurry is then cast to form sheets of uniform thickness (about 100 μm - 500 μm). Once dried, these so-called Green Sheets can be easily cut, rolled up for transport, and processed further.
The next step in the production involves the definition of the electrical conducting lines. Depending on the design, the sheets are punched to form cavities and vias, which can be filled with a metal paste. These vias create vertical connections for the electrical feedthroughs. The planar electrical lines are defined on the ceramic sheets by screen-printing, again using refractory metal pastes.
Once the various metal structures are defined, the ceramic sheets are stacked in a specific order and laminated. This process connects the individual, basically two dimensional sheets and ends up in a three dimensional structure with hermetic electrical feedthroughs. In data communication, the cross section of this three dimensional structure often is similar to a "T", which is why the finished ceramic product is also called a T-bar.
The multilayer ceramic is co-fired at high temperatures to form a solid and hermetic ceramic. For HTCC a final metal coating (e.g. a plated Ni or Ni/Au coating) on the accessible metal structures offers the possibility for high temperature brazing (using e.g. AgCu eutectic) or low temperature soldering (e.g. AuSn eutectic) process steps. By this the ceramic feedthrough component can be combined with an even more complex metal housing, providing an extremely reliable hermetic package with various customized mechanical, electrical, optical and thermal functionalities.
Advantages of Multilayer Ceramic Technology:
- Customized solutions based on a variety of manufacturing processes
- Efficient solutions due to high degree of design support from the beginning of the product development cycle
- Availability of a variety of mechanical, thermal (ANSYS, ABACUS), optical (ZEMAX) and electrical (HFSS, ADS) simulation tools
- Worldwide customer support from local manufacturing facilities with technical competence centers
Characteristics of HTCC:
- Excellent mechanical stability
- Easy integration into metal housings due to matched thermal coefficient of expansion
- High thermal conductivity
- Use of non-noble metal pastes
- Additional plating reveals solderable and wirebondable surfaces
Characteristics of LTCC:
- Excellent HF properties provided by low dielectric losses and high conductivity metal
- High electrical conductivity of metal patterns
- Realization of hermetic packages by fluxless soldering processes
- Embedded passive components (resistors, inductors, capacitors) provide space saving solutions
- Variety of product options are available based on different tape and metal paste systems