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Ahybrid integrated circuit (HIC),hybrid microcircuit,hybrid circuit or simplyhybrid is a miniaturizedelectronic circuit constructed of individual devices, such assemiconductor devices (e.g.transistors,diodes ormonolithic ICs) and passive components (e.g.resistors,inductors,transformers, andcapacitors), bonded to a substrate orprinted circuit board (PCB).[1] A PCB having components on aprinted wiring board (PWB) is not considered a true hybrid circuit according to the definition ofMIL-PRF-38534.
"Integrated circuit", as the term is currently used, usually refers to a monolithic IC which differs notably from a HIC in that a HIC is fabricated by inter-connecting a number of components on a substrate whereas an IC's (monolithic) components are fabricated in a series of steps entirely on a single wafer which is then diced into chips.[2] Some hybrid circuits may contain monolithic ICs, particularlymulti-chip module (MCM) hybrid circuits.
Hybrid circuits could be encapsulated inepoxy, as shown in the photo, or in military and space applications, a lid wassoldered onto the package. A hybrid circuit serves as a component on a PCB in the same way as a monolithicintegrated circuit; the difference between the two types of devices is in how they are constructed and manufactured. The advantage of hybrid circuits is that components which cannot be included in a monolithic IC can be used, e.g., capacitors of large value, wound components, crystals, inductors.[3] In military and space applications, numerous integrated circuits, transistors and diodes, in their die form, would be placed on either a ceramic or beryllium substrate. Either gold or aluminium wire would be bonded from the pads of the IC, transistor, or diode to the substrate.
Thick-film technology is often used as the interconnecting medium for hybrid integrated circuits. The use of screen printed thick film interconnect provides advantages of versatility over thin film although feature sizes may be larger and deposited resistors wider in tolerance. Multi-layer thick film is a technique for further improvements in integration using a screen printed insulating dielectric to ensure connections between layers are made only where required. One key advantage for the circuit designer is complete freedom in the choice of resistor value in thick film technology. Planar resistors are also screen printed and included in the thick film interconnect design. The composition and dimensions of resistors can be selected to provide the desired values. The final resistor value is determined by design and can be adjusted bylaser 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 forConcorde.
Some modern hybrid circuit technologies, such asLTCC-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.
Hybrid ICs are especially suitable for analog signals. They were used in some early digital computers but were replaced therein by monolithic ICs which offered higher performance.[4][5][6]
In the early days of telephones, separate modules containing transformers and resistors were called hybrids orhybrid coils; they have been replaced by semiconductorintegrated circuits.
In the early days oftransistors the termhybrid circuit was used to describe circuits with both transistors andvacuum tubes; e.g., anaudio 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 calledhybrid amplifiers in reference to this.
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