In the late 1950s, the U. S. Army Signal Corps. program, with RCA as prime contractor, developed hybrid microcircuits as dense micro-module assemblies of electronic components. Hybrid circuits comprise one or more transistor chips and passive components mounted on ceramic substrates and interconnected with wires or conductive traces. After the introduction of monolithic ICs, functions that required high-density packaging and that could not be integrated for economic or technical reasons continued to be manufactured as hybrids. Examples include precision analog devices, automotive controls, and early semiconductor memories.
IBM developed Solid Logic Technology (SLT) for the System/360 computer family in 1964 prior to the ability of monolithic ICs to meet the cost and speed demands of large computers. Transistor chips and passive components mounted on 0.5" square ceramic modules with vertical pins consumed less power and space while offering faster speed and superior reliability compared to printed-circuit boards with packaged transistors. IBM produced hundreds of millions of SLT modules in a highly-automated, specially-built plant in East Fishkill, NY. Bell Laboratories used Beam Lead Sealed-Junction (BLSJ) devices and thin-film interconnects (1965 Milestone) to produce hybrid ICs for telephone systems through the late-1960s.
Early hand-crafted hybrid circuits were labor intensive and expensive to produce but are now widely used in applications where integrated devices cannot meet specific objectives. Multichip modules (MCM) and packages (MCP) are modern machine-assembled hybrid circuits, used for certain high-performance microprocessor and memory applications, automotive systems, and RF transceivers in cell phones and wireless LANs.
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