Low temperature co-fired ceramic

Low temperature co-fired ceramic (LTCC) devices are monolithic, ceramic microelectronic devices. In this context ‘co-fired ceramic’ means that the ceramic support structure and any conductive, resistive, and dielectric materials are fired in a kiln at the same time, and ‘Low temperature’ means that the sintering, temperature is less than 1000 °C. LTCC devices include capacitors, inductors, resistors, transformers, and hybrid circuits. LTCC processes can also be used to make packages for ICs. LTCC 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.

History

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

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.

Advantages

This technology presents advantages compared to other packaging technologies such as HTCC: the ceramic is generally fired below 1000°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.

See also

• High temperature co-fired ceramic (HTCC)
• Tape casting
• Laser trimming
• Hybrid integrated circuit

External links

• LTCC Technology description of LTCC and related drawings
• Kyocera LTCC drawings showing an LTCC hybrid circuit stack up