Solid Logic Technology

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 and related machines. 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).

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

IBM considered monolithic integrated circuit technology too immature at the time. 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.

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