Co-fired ceramic

Co-fired ceramic devices are monolithic, ceramic 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, inductors, resistors, transformers, and hybrid circuits. The technology is also used for a multi-layer packaging for the electronics industry, such as military electronics, MEMS, microprocessor and RF applications.[1]

Co-fired ceramic devices are made by processing a number of layers independently and assembling them into a device as a final step. This differs from semiconductor device fabrication where layers are processed serially; each new layer being fabricated on top of previous layers.

Co-firing can be divided into low temperature (LTCC) and high temperature (HTCC) applications: low temperature means that the sintering temperature is below 1,000 °C (1,830 °F), while high temperature is around 1,600 °C (2,910 °F).[2] Compared to LTCC, HTCC has higher resistance conductive layers.

History

Co-fired ceramics were first developed in the late '50s and early '60s to make more robust capacitors.[3] The technology was later expanded in the '60s to include multilayer printed circuit board like structures.[4]

Components

Hybrid circuits

LTCC technology is especially beneficial for RF and high-frequency applications. In RF and wireless 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. LTCC hybrids have a smaller initial ("non recurring") cost as compared with ICs, making them an attractive alternative to ASICs 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 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 include 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 means these transformers are not prone to wire break failures in high mechanical stress environments.[5]

Sensors

Integration of thick-film passive components and 3D mechanical structures inside one module permitted the fabrication of sophisticated 3D LTCC sensors e.g. accelerators.[6]

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.[7]

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 packages generally consist of multilayers of alumina oxide with tungsten and molymanganese metalization. The advantages of HTCC 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.[8]

See also

References

  1. ↑ Microwave 101 Website
  2. ↑ AMETEK ECP Website http://www.ametek-ecp.com/Products/MicroelectronicPackages/HTCC.aspx
  3. ↑ US 3004197, Rodriguez, Antonio R. & Arthur B. Wallace, "Ceramic capacitor and method of making it", issued 10/10/1961
  4. ↑ US 3189978, Stetson, Harold W., "Method of making multilayer circuits", issued 06/22/1965
  5. ↑ Roesler, Alexander W.; Schare, Joshua M.; Glass, S. Jill; Ewsuk, Kevin G.; Slama, George; Abel, David; Schofield, Daryl (June 2010), "Planar LTCC Transformers for High-Voltage Flyback Converters", IEEE Transactions on Components and Packaging Technologies 33 (2): 359–372, doi:10.1109/tcapt.2009.2031872
  6. ↑ Jurków, Dominik (2013). "Three axial low temperature cofired ceramic accelerometer" (PDF). Microelectronics International 30 (3): 125–133. doi:10.1108/MI-11-2012-0077.
  7. ↑ Golonka, Leszek; Pawel Bembnowicz; Dominik Jurkow; Karol Malecha; Henryk Roguszczak; Rafal Tadaszak (2011). "Low temperature co-fired ceramics (LTCC) microsystems" (PDF). Optica Applicata 41 (2): 383–388. Retrieved 5 May 2014.
  8. ↑ Millimeter-wave Performance of Alumina High Temperature Cofired Ceramics IC Packages, Rick Sturdivant, 2006 IMAPS Conference, San Diego, CA

External links

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