and can be adjusted by laser trimming. Once the hybrid circuit is fully populated with components, fine tuning prior to final test may be achieved by active laser trimming. Thin film technology was also employed in the 1960s. Ultra Electronics manufactured circuits using a silica glass substrate. A film of tantalum was deposited by sputtering followed by a layer of gold by evaporation. The gold layer was first etched following the application of a photoresist to form solder compatible connection pads. Resistive networks were formed, also by a photoresist and etching process. These were trimmed to a high precision by selective adonization of the film. Capacitors and semiconductors were in the form of LID (Leadless Inverted Devices) soldered to the surface by selectively heating the substrate from the underside. Completed circuits were potted in a diallyl phthalate resin. Several customized passive networks were made using these techniques as were some amplifiers and other specialized circuits. It is believed that some passive networks were used in the engine control units manufactured by Ultra Electronics for Concorde. Some modern hybrid circuit technologies, such as LTCC-substrate hybrids, allow for embedding of components within the layers of a multi-layer substrate in addition to components placed on the surface of the substrate. This technology produces a circuit that is, to some degree, three-dimensional. Other electronic hybrids In the early days of telephones, separate modules containing transformers and resistors were called hybrids or hybrid coils; they have been replaced by semiconductor integrated circuits. In the early days of transistors the term hybrid circuit was used to describe circuits with both transistors and vacuum tubes; e.g., an audio amplifier with transistors used for voltage amplification followed by a vacuum tube power output stage, as suitable power transistors were not available. This usage, and the devices, are obsolete, however amplifiers that use a tube preamplifier stage coupled with a solid state output stage are still in production, and are called hybrid amplifiers in reference to this. See also Chip on board, aka black blobs System in a package Multi-chip module (MCM) Monolithic microwave integrated circuit (MMIC) Solid Logic Technology (SLT) MIL-PRF-38534 Printed Circuit Board (PCB) Printed Electronic Circuit - Ancestor of the Hybrid IC References External links Electronic circuits