Editing Solid Logic Technology

{{Short description|IBM hybrid circuit technology introduced in 1964}}
{{multiple image|total_width=330px|header=Solid Logic Technology cards
|image1=Slt1.jpg|caption1=A double-width SLT card. The square metal cans contain the hybrid circuits.
|image2=IBM SLT cards, three.agr.jpg|caption2=Three single-width SLT cards
}}
{{multiple image|total_width=330px|header=SLT cards ''in situ''
|image1=SLT Card Frame.corestore.jpg|caption1=Many SLT cards plugged into a board
|image2=IBM 129 SLT modules.jpg|caption2=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 [[IBM 1130|1130]], announced in 1965. IBM chose to design custom [[hybrid circuit]]s using discrete, [[flip chip]]-mounted, [[glass]]-encapsulated [[transistor]]s and [[diode]]s, with [[screen-printing|silk-screened]] [[resistor]]s 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.<ref name=boyer>{{cite web|url=http://www.computer-museum.ru/books/archiv/ibm36040.pdf |title=The 360 Revolution |last=Boyer |first=Chuck |date=April 2004 |publisher=IBM |page=18 |accessdate=27 May 2018}}</ref> SLT was a revolutionary technology for 1964, with much higher circuit densities and improved reliability over earlier packaging techniques such as the [[IBM Standard Modular System|Standard Modular System]]. It helped propel the IBM System/360 mainframe family to overwhelming success during the 1960s. SLT research produced ball chip assembly, [[flip chip|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 circuit]]s that held four or five transistors. MST was used in the [[System/370]], which began to replace the System/360 in 1970.

==Details==
SLT used silicon planar glass-encapsulated transistors and diodes.<ref name=Evans>{{cite journal |title=Solid Logic Technology: Versatile, High-Performance Microelectronics |last1=Davis|first1=E.M. |last2=Harding |first2=W.E. |last3=Schwartz |first3=R.S. |last4=Corning |first4=J.J. |journal=IBM Journal of Research and Development |volume=8|issue=2 |pages=102–114| doi=10.1147/rd.82.0102|date=April 1964|s2cid=13288023 }}</ref>

SLT uses dual diode chips and individual transistor chips each approximately {{convert|0.025|inch}} square.<ref name=ALD/>{{rp|15}} The chips are mounted on a {{convert|0.5|inch}} square substrate with silk-screened resistors and printed connections. The whole is encapsulated to form a {{convert|0.5|inch}} square module. Up to 36 modules are mounted on each card, though a few card types had just discrete components and no modules. Cards plug into boards which are connected to form gates which form frames.<ref name=ALD/>{{rp|15}}

SLT voltage levels, logic low to logic high, varied by circuit speed:<ref name=ALD/>{{rp|16}}

:High speed (5-10 ns) 0.9 to 3.0 V
:Medium speed (30 ns) 0.0 to 3.0 V
:Low speed (700 ns) 0.0 to 12.0 V

{{plain image with caption|IBM SLT wafers.agr.JPG|align=center|width=800px|caption=Steps in manufacturing Solid Logic Technology hybrid modules. The process starts with a blank ceramic wafer, {{convert|1/2|in|mm}} square. Circuits are laid down first, followed by resistive material. Pins are added, the circuits are soldered and the resistors trimmed to the desired value. Then individual transistors and diodes are added and the package is encapsulated.|triangle=triangle}}

==Later developments==
The same basic packaging technology (both device and module) was also used for the devices that replaced SLT as IBM gradually transitioned to the use of 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.<ref name=ALD>[http://www.bitsavers.org/pdf/ibm/logic/SY22-2798-2_LogicBlocks_AutomatedLogicDiagrams_SLT,SLD,ASLT,MST_TO_Oct71.pdf Logic Blocks Automated Logic Diagrams SLT, SLD, ASLT, MST] (PDF) 86 pages</ref>{{rp|15}} SLD voltages were the same as SLT.
* Unit Logic Device (ULD) use flat-pack ceramic packages, much smaller than SLT's metal cans. Each package contains a ceramic wafer with up to four silicon dies on top, each die implementing one transistor or two diodes; and thick-film resistors underneath. ULDs were used in the [[Launch Vehicle Digital Computer]] and Launch Vehicle Data Adapter of the [[Saturn V]] rocket.<ref>
Ken Shirriff.
[http://www.righto.com/2020/04/a-circuit-board-from-saturn-v-rocket.html "A circuit board from the Saturn V rocket, reverse-engineered and explained"].
2020.
</ref><ref>
Dr. Wernher von Braun.
[https://books.google.com/books?id=4SUDAAAAMBAJ&pg=PA94 "Tiny Computers Steer Mightiest Rockets"].
Popular Science.
Oct 1965.
p. 94-95; 206-208.
</ref>
*Advanced Solid Logic Technology (ASLT) increased packaging density and circuit performance by stacking two substrates in the same package. ASLT is based on the [[Emitter-follower-coupled-switch]] used with [[Emitter-coupled logic|current-steering logic]].<ref name=ALD/>{{rp|18}} ASLT voltage levels were : > +235 mV is high, < -239 mV is low.<ref name=ALD/>{{rp|16}}
{{anchor|IBM_MST}}<!-- do not remove, will be linked -->
*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). Each MST chip holds about five circuits and is the approximate equivalent of an SLT card.<ref name=ALD/>{{rp|18}} Circuits used [[NPN transistor]]s. MST was first introduced in January 1968 and provided improved cost/performance for IBM's System/370 product line of the 1970s.<ref>{{cite book
 |url=https://books.google.com/books?id=MFGj_PT_clIC&dq=%22IBM%27s+360+and+Early+370+Systems%22+425&pg=PA425
 |title=IBM's 360 and Early 370 System |last1=Pugh|first1=Emerson W.  |last2=Johnson  |first2=Lyle R. |last3=Palmer  |first3=John H.   
 |year=1991 |page=425 |publisher=MIT Press |isbn=9780262161237 |access-date=August 8, 2022}}</ref>

==Gallery==
<gallery mode=packed >
File:Modulo per computer tipo SLT (Solid Logic Technology) - Museo scienza tecnologia Milano D1188.jpg|Monolithic System Technology card with module covers removed
File:SLT_half-card.jpg|An uncommon half-width SLT card with no SLT modules
File:IBM SLT card, single width.jpg|Single-width card
File:IBM SLT module, quad width.jpg|right|Quad-width SLT module
File:IBM SLT chip, top and bottom.jpg|right|Module with six transistors and three resistors, cap off
File:IBM SLT chip, side view.jpg|Closeup shows the raised squares of the transistors and the flat black resistors
</gallery>

== See also ==
* [[Standard Modular System]]

==References==
<references/>

==External links==
{{commons category}}
*{{cite journal|title=Solid Logic Technology: Versatile, High-Performance Microelectronics|last1=Davis|first1=E.M.|last2=Harding|first2=W.E.|last3=Schwartz|first3=R.S.|last4=Corning|first4=J.J.|journal=IBM Journal of Research and Development|volume=8|issue=2|pages=102–114|doi=10.1147/rd.82.0102|date=April 1964|s2cid=13288023 }}
*[http://www.chipsetc.com/the-ibm-slt---solid-logic-technology.html IBM's Solid Logic Technology (SLT) 1964-1968], Vintage Computer Chips, includes video of automated manufacturing process

[[Category:Chip carriers]]
[[Category:IBM System/360 mainframe line|Solid Logic Technology]]
[[Category:IBM computer hardware|Solid Logic]]
[[Category:Printed circuit board manufacturing]]
[[Category:Computer-related introductions in 1964]]