Co-fired Ceramic
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Co-fired ceramic devices are
monolithic A monolith is a monument or natural feature consisting of a single massive stone or rock. Monolith or monolithic may also refer to: Architecture * Monolithic architecture, a style of construction in which a building is carved, cast or excavated f ...
,
ceramic A ceramic is any of the various hard, brittle, heat-resistant, and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcela ...
microelectronic devices where the entire ceramic support structure and any conductive, resistive, and dielectric materials are fired in a kiln at the same time. Typical devices include
capacitors In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...
,
inductors An inductor, also called a coil, choke, or reactor, is a passive two-terminal electrical component that stores energy in a magnetic field when an electric current flows through it. An inductor typically consists of an insulated wire wound into a ...
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resistors A resistor is a passive two-terminal electronic component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active e ...
,
transformer In electrical engineering, a transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple Electrical network, circuits. A varying current in any coil of the transformer produces ...
s, and hybrid circuits. The technology is also used for robust assembly and packaging of electronic components multi-layer
packaging Packaging is the science, art and technology of enclosing or protecting products for distribution, storage, sale, and use. Packaging also refers to the process of designing, evaluating, and producing packages. Packaging can be described as a coo ...
in the electronics industry, such as military electronics,
MEMS MEMS (micro-electromechanical systems) is the technology of microscopic devices incorporating both electronic and moving parts. MEMS are made up of components between 1 and 100 micrometres in size (i.e., 0.001 to 0.1 mm), and MEMS devices ...
,
microprocessor A microprocessor is a computer processor (computing), processor for which the data processing logic and control is included on a single integrated circuit (IC), or a small number of ICs. The microprocessor contains the arithmetic, logic, a ...
and RF applications. Co-fired ceramic devices are fabricated using a multilayer approach. The starting material is composite green tapes, consisting of ceramic particles mixed with polymer binders. The tapes are flexible and can be machined, for example, using cutting, milling, punching and embossing. Metal structures can be added to the layers, commonly using filling and screen printing. Individual tapes are then bonded together in a lamination procedure before the devices are fired in a kiln, where the polymer part of the tape is combusted and the ceramic particles sinter together, forming a hard and dense ceramic component. Co-firing can be divided into low-temperature (LTCC) and high-temperature (HTCC) applications: low temperature means that the
sintering Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction. Sintering happens as part of a manufacturing process used with metals, ceramics, plas ...
temperature is below , while high temperature is around . The lower sintering temperature for LTCC materials is made possible through the addition of a glassy phase to the ceramic, which lowers its melting temperature. Due to a multilayer approach based on glass-ceramics sheets, this technology offers the possibility to integrate into the LTCC body passive electrical components and conductor lines typically manufactured in thick-film technology. This differs from
semiconductor device fabrication Semiconductor device fabrication is the process used to manufacture semiconductor devices, typically integrated circuits (ICs) such as microprocessors, microcontrollers, and memories (such as Random-access memory, RAM and flash memory). It is a ...
, where layers are processed serially, and each new layer is fabricated on top of previous layers.


History

Co-fired ceramics were first developed in the late 1950s and early 1960s to make more robust capacitors. The technology was later expanded in the 1960s to include multilayer structures similar to printed circuit boards.


Components


Hybrid circuits

LTCC technology is especially beneficial for RF and high-frequency applications. In RF and
wireless Wireless communication (or just wireless, when the context allows) is the transfer of information (''telecommunication'') between two or more points without the use of an electrical conductor, optical fiber or other continuous guided transm ...
applications, LTCC technology is also used to produce multilayer hybrid integrated circuits, which can include resistors, inductors, capacitors, and active components in the same package. In detail, these applications comprise mobile telecommunication devices (0.8–2 GHz),
wireless Wireless communication (or just wireless, when the context allows) is the transfer of information (''telecommunication'') between two or more points without the use of an electrical conductor, optical fiber or other continuous guided transm ...
local networks such as
Bluetooth Bluetooth is a short-range wireless technology standard that is used for exchanging data between fixed and mobile devices over short distances and building personal area networks (PANs). In the most widely used mode, transmission power is li ...
(2.4 GHz) to in-car
radars Radar is a system that uses radio waves to determine the distance ('' ranging''), direction (azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track aircr ...
(50–140 GHz, and 76 GHz). LTCC hybrids have a smaller initial ("non recurring") cost as compared with ICs, making them an attractive alternative to
ASIC An application-specific integrated circuit (ASIC ) is an integrated circuit (IC) chip customized for a particular use, rather than intended for general-purpose use, such as a chip designed to run in a digital voice recorder or a high-efficien ...
s for small scale integration devices.


Inductors

Inductors are formed by printing conductor windings on ferrite ceramic tape. Depending on the desired inductance and current carrying capabilities a partial winding to several windings may be printed on each layer. Under certain circumstances, a non-ferrite ceramic may be used. This is most common for hybrid circuits where capacitors, inductors, and resistors will all be present and for high operating frequency applications where the
hysteresis Hysteresis is the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of ...
loop of the ferrite becomes an issue.


Resistors

Resistors may be embedded components or added to the top layer post-firing. Using screen printing, a resistor paste is printed onto the LTCC surface, from which resistances needed in the circuit are generated. When fired, these resistors deviate from their design value (±25%) and therefore require adjustment to meet the final tolerance. With Laser trimming one can achieve these resistances with different cut forms to the exact resistance value (±1%) desired. With this procedure, the need for additional discrete resistors can be reduced, thereby allowing a further miniaturization of the printed circuit boards.


Transformers

LTCC transformers are similar to LTCC inductors except transformers contain two or more windings. To improve coupling between windings transformers includes a low-permeability dielectric material printed over the windings on each layer. The monolithic nature of LTCC transformers leads to a lower height than traditional wire wound transformers. Also, the integrated core and windings mean these transformers are not prone to wire break failures in high mechanical stress environments.


Sensors

Integration of thick-film passive components and 3D mechanical structures inside one module permitted the fabrication of sophisticated 3D LTCC sensors e.g. accelerometers.


Microsystems

The possibility of the fabrication of many various passive thick-film components, sensors and 3D mechanical structures enabled the fabrication of multilayer LTCC microsystems. Using HTCC technology, microsystems for harsh environments, such as working temperatures of 1000 °C, have been realized.


Applications

LTCC substrates can be most beneficially used for the realization of miniaturized devices and robust substrates. LTCC technology allows the combination of individual layers with different functionalities such as high permittivity and low dielectric loss into a single multilayer laminated package and thereby to achieve multi-functionality in combination with a high integration and interconnection level. It also provides the possibility to fabricate three-dimensional, robust structures enabling in combination with thick film technology the integration of passive, electronic components, such as capacitors, resistors, and inductors into a single device.


Comparison

Low-temperature co-firing technology presents advantages compared to other packaging technologies including high-temperature co-firing: the ceramic is generally fired below 1,000 °C due to a special composition of the material. This permits the co-firing with highly conductive materials (silver, copper, and gold). LTCC also features the ability to embed passive elements, such as resistors, capacitors and inductors into the ceramic package, minimising the size of the completed module. HTCC components generally consist of multilayers of
alumina Aluminium oxide (or aluminium(III) oxide) is a chemical compound of aluminium and oxygen with the chemical formula . It is the most commonly occurring of several aluminium oxides, and specifically identified as aluminium oxide. It is commonly ...
or
zirconia Zirconium dioxide (), sometimes known as zirconia (not to be confused with zirconium silicate or zircon), is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the mineral ba ...
with platinum, tungsten and moly-manganese metalization. The advantages of HTCC in packaging technology includes mechanical rigidity and hermeticity, both of which are important in high-reliability and environmentally stressful applications. Another advantage is HTCC's thermal dissipation capability, which makes this a microprocessor packaging choice, especially for higher-performance processors.Millimeter-wave Performance of Alumina High Temperature Cofired Ceramics IC Packages
, Rick Sturdivant, 2006 IMAPS Conference, San Diego, CA.
Compared to LTCC, HTCC has higher- resistance conductive layers.


See also

*
Tape casting Tape casting (also called doctor blading and knife coating) is a casting process used in the manufacture of thin ceramic tapes and sheets from ceramic slurry. The ceramic slurry is cast in a thin layer onto a flat surface and then dried and sinterin ...
* Laser trimming


References

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External links


Animation of LTCC production process
Packaging (microfabrication) Electronics manufacturing