IBM Solid Logic Technology
Solid Logic Technology (SLT) was IBM's method for packaging electronic circuitry introduced in 1964 with the IBM System/360 series 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. The circuits were either encapsulated in plastic or covered with a metal lid. Several of these were then mounted on a small multi-layer printed circuit board to make an SLT module. Each SLT module 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). SLT was a revolutionary technology for 1964 with the reliability improvements over other assembly techniques helping propel the IBM/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.
The same basic packaging technology (both device and module) was also used for the devices that replaced SLT as IBM gradually transitioned from hybrid integrated circuits to monolithic integrated circuits:
- Solid Logic Dense (SLD) increased packaging density and circuit performance by mounting the discrete transistors and diodes on top of the substrate and the resistors on the bottom.
- Advanced Solid Logic Technology (ASLT) increased packaging density and circuit performance by stacking two substrates in the same package.
- Monolithic System Technology (MST) increased packaging density and circuit performance by replacing discrete transistors and diodes with one to four monolithic integrated circuits (resistors now external from the package on the module).