LTCC technology involves the production of multilayer circuits from ceramic substrate tapes or sheets. Conductive, dielectric, and resistive pastes are applied on each sheet or tape as needed, and then the sheets are laminated-together and fired (often in a precisely controlled oven or kiln) in one step. The resulting design is a hermetic, monolithic structure (see figure). A typical LTCC structure consists of multiple dielectric layers; screen-printed or photo-imaged low-loss conductors; embedded baluns, resistors and capacitors; and viaholes for interconnecting the multiple layers.
Each layer can be inspected before firing to replace damaged circuits and improve yield. Because firing takes place at low temperatures, typically about +850 °ree;C, low-resistivity conductor materials such as silver and gold can be used on LTCC instead of the molybdenum and tungsten materials typically used with hightemperaturecofired-ceramic (HTCC) processes. Since LTCC is a repeatable process, it can reliably produce large quantities of RF and microwave components measuring a fraction of the size of components fabricated with conventional substrate materials.
For practical and cost-effective use of LTCC technology, Mini-Circuits has developed a series of three-dimensional computer models using the latest electromagnetic (EM) simulation tools. These proven computer models make it possible to develop new and custom components quickly, economically, and reliably with a high-degree of first-pass design success.
LTCC technology yields a highly-integrated surface-mount module that can in turn be used as a platform to mount active components, such as transistors, diode quads, and monolithic amplifiers, to form a miniature multifunction assembly. The resulting LTCC unit is a multilayer, three-dimensional design that is considerably more compact than a traditional planar microwave component. High-level integration allows LTCC components to be combined within a miniature surface-mount package, eliminating the need for many external components. Moreover, LTCC designs can employ circuit elements in die form for further reduction in size. Since the ceramic materials used in LTCC designs are inherently very temperature stable, the need to compensate for variations in temperature is greatly reduced.
