Multi-chip SLT packaging technology developed for the IBM System/360 computer family enters mass production.

A 1950s U. S. National Bureau of Standards program called “Project Tinkertoy” encouraged the development of hybrid microcircuits and dense modular assemblies of electronic components. Hybrid circuits comprise multiple 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 high-density semiconductor memory systems.

The highest volume hybrid circuit program was Solid Logic Technology (SLT) developed by IBM for the System/360 computer family in 1964 prior to the availability of monolithic ICs meeting the cost and performance demands of large computer systems. Bare transistor chips and passive components were mounted on half-inch square ceramic modules with vertical pin connections. They 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.

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.