Solid Logic Technology
| Company type | Technology / Packaging approach |
|---|---|
| Industry | Electronics, Computer hardware |
| Founded | 1964 |
| Founder | IBM |
| Products | Hybrid circuit modules and cards used in IBM System/360 and IBM 1130 |
| Parent | IBM |
Solid Logic Technology (SLT) represented IBM's hybrid circuit packaging approach introduced in 1964 alongside the IBM System/360 series and later utilized in the IBM 1130, which was announced in 1965. IBM engineered custom hybrid circuits comprising discrete silicon transistors and diodes mounted using flip chip technology and encapsulated within glass. These components were integrated with silk-screened resistors on a ceramic base, forming what became known as an SLT module. The modules were either enclosed in plastic or sealed under a metal cover. Multiple SLT modules—20 are depicted in the accompanying image—were assembled onto a multilayer printed circuit board to form an SLT card. Each card featured a socket edge connector that interfaced with pins on the computer’s backplane, differing from the designs typically employed by competitors at the time.
During this period, IBM considered monolithic integrated circuit technology to be insufficiently mature for their needs. SLT was a groundbreaking innovation for 1964, delivering greater circuit density and enhanced reliability compared to previous packaging systems such as the IBM Standard Modular System. This advancement played a crucial role in securing the IBM System/360’s leading position in the marketplace throughout the 1960s. The development of SLT introduced several pioneering manufacturing techniques including ball chip assembly, wafer bumping, trimmed thick-film resistors, printed discrete functions, chip capacitors, and one of the earliest widespread applications of hybrid thick-film technology.
SLT succeeded the Standard Modular System as IBM’s primary packaging technology, although some later SMS cards incorporated SLT modules. The subsequent progression was Monolithic System Technology (MST), which replaced single transistors with small-scale integrated circuits containing about four or five transistors each. MST was deployed in the System/370, which began replacing the System/360 starting in 1970.
Details
SLT utilized silicon planar transistors and diodes that were encapsulated in glass.
The technology incorporated dual diode chips and individual transistor chips roughly square in dimension. These chips were mounted on a ceramic substrate approximately square, which featured silk-screened resistors and printed wiring paths, all enclosed within a square module. Cards could hold as many as 36 such modules; however, certain card types contained only discrete components without modules. The cards plugged into boards that formed logic gates, which were then assembled into frames.
Voltage levels for SLT circuits varied depending on their speed classification:
- High speed (5–10 ns) operated between 0.9 and 3.0 volts
- Medium speed (30 ns) ranged from 0.0 to 3.0 volts
- Low speed (700 ns) spanned from 0.0 up to 12.0 volts
Later developments
As IBM transitioned from SLT toward monolithic integrated circuits, they adapted this packaging method into several subsequent technologies:
- Solid Logic Dense (SLD) enhanced packaging density and improved circuit performance by positioning discrete transistors and diodes on top of the substrate while placing resistors underneath. SLD operated at voltage levels comparable to those of SLT.
- Unit Logic Device (ULD) consisted of smaller flat-pack ceramic packages housing a ceramic wafer containing up to four silicon dies, each incorporating transistors or diodes, along with thick-film resistors beneath. ULDs were notably used in the Launch Vehicle Digital Computer and Launch Vehicle Data Adapter systems of the Saturn V rocket.
- Advanced Solid Logic Technology (ASLT) achieved further increases in density and performance by stacking two substrates within a single package; it employed emitter-follower-coupled-switch current-steering logic. ASLT signal voltages were greater than +235 mV for high states and less than -239 mV for low states.
- Monolithic System Technology (MST) phased out discrete transistors and diodes in favor of packages containing one to four monolithic integrated circuits per module, with resistors located externally on the module itself. Each MST chip comprised about five circuits—roughly equivalent in complexity to an SLT card. Introduced in January 1968, MST improved cost-efficiency and performance for IBM’s System/370 computers during the 1970s.
See also
References
External links
- Overview of IBM's Solid Logic Technology (SLT) 1964-1968, Vintage Computer Chips, including footage of automated production