Solid Logic Technology

Solid Logic Technology cards

A double-width SLT card. The square metal cans contain the hybrid circuits.

Three single-width SLT cards

SLT cards in situ

Many SLT cards plugged into a board

SLT cards in an IBM 129 keypunch

Solid Logic Technology (SLT) was IBM's method for hybrid packaging of electronic circuitry introduced in 1964 with the IBM System/360 series of computers. It was also used in the 1130, announced in 1965. IBM chose to design custom hybrid circuits using discrete, flip chip-mounted, glass-encapsulated transistors and diodes, with silk-screened resistors on a ceramic substrate, forming an SLT module. The circuits were either encapsulated in plastic or covered with a metal lid. Several of these SLT modules (20 in the image on the right) were then mounted on a small multi-layer printed circuit board to make an SLT card. Each SLT card had a socket on one edge that plugged into pins on the computer's backplane (the exact reverse of how most other companies' modules were mounted).

IBM considered monolithic integrated circuit technology too immature at the time.^[1] SLT was a revolutionary technology for 1964, with much higher circuit densities and improved reliability over earlier packaging techniques such as the Standard Modular System. It helped propel the IBM System/360 mainframe family to overwhelming success during the 1960s. SLT research produced ball chip assembly, wafer bumping, trimmed thick-film resistors, printed discrete functions, chip capacitors and one of the first volume uses of hybrid thick-film technology.

SLT replaced the earlier Standard Modular System, although some later SMS cards held SLT modules. SLT had several updates during its life, the last being the Monolithic System Technology (MST) which replaced the single transistors of SLT with small-scale integrated circuits that held four or five transistors. MST was used in the System/370, which began to replace the System/360 in 1970.