TO-3

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Metal can semiconductor package for power semiconductors

title: "TO-3" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["semiconductor-packages"] description: "Metal can semiconductor package for power semiconductors" topic_path: "general/semiconductor-packages" source: "https://en.wikipedia.org/wiki/TO-3" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Metal can semiconductor package for power semiconductors ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/2/21/Transistorer_(cropped).jpg" caption="BJT transistor]] packages, from left to right: [[SOT-23]], [[TO-92]], [[TO-126]], TO-3"] ::

::figure[src="https://upload.wikimedia.org/wikipedia/commons/f/fb/TO-3_transistor_package.stl" caption="3D model of TO-3 package"] ::

In electronics, TO-3 is a designation for a standardized metal semiconductor package used for power semiconductors, including transistors, silicon controlled rectifiers, and, integrated circuits. TO stands for "Transistor Outline" and relates to a series of technical drawings produced by JEDEC.

The TO-3 case has a flat surface which can be attached to a heatsink, normally via a thermally conductive but electrically insulating washer. The design originated at Motorola around 1955 from a group headed by Dr. Virgil E. Bottom.{{Cite book |last=Bottom |first=Virgil |title=FROM POSSUM HOLLER TO SINGAPORE The Autobiography of VIRGIL E. BOTTOM|date= November 1992 |publisher=Self published |page=177 |url=http://www.ieee-uffc.org/main/history-bottombio.asp |archive-url=https://web.archive.org/web/20160315010403/http://www.ieee-uffc.org/main/history-bottombio.asp |archive-date=2016-03-15 |access-date=2022-08-22 |chapter=XIII Phoenix 1953–1958 |chapter-url=http://www.ieee-uffc.org/main/history/Bottom/chapter13.doc |chapter-format=DOC}} who was director of research of the Motorola Semiconductor Division. The first use of this design was for the germanium alloy-junction power transistor 2N176 – the first power transistor to be put into quantity production. The lead spacing was originally intended to allow plugging the device into a then-common tube socket.

Typical applications

::figure[src="https://upload.wikimedia.org/wikipedia/commons/f/f0/TO-3_mounting.png" caption="Typical TO-3 mounting profile, with insulator from chassis"] ::

The metal package can be attached to a heat sink, making it suitable for devices dissipating several watts of heat. Thermal compound is used to improve heat transfer between the device case and the heat sink. Since the device case is one of the electrical connections, an insulator may be required to electrically isolate the component from the heatsink. Insulating washers may be made of mica or other materials with good thermal conductivity.

The case is used with high-power and high-current devices, on the order of a few tens of amperes current and up to a hundred watts of heat dissipation. The case surfaces are metal for good heat conductivity and durability. The metal-to-metal and metal-to-glass joints provide hermetic seals that protect the semiconductor from liquids and gases.

Compared with equivalent plastic packages, the TO-3 is more costly. The spacing and dimensions of the case leads make it unsuitable for higher frequency (radio frequency) devices.

Construction

::figure[src="https://upload.wikimedia.org/wikipedia/commons/d/d9/Darlington_transistor_MJ1000.jpg" caption="Inside of an MJ1000 [[Darlington transistor]] in TO-3 package"] ::

The semiconductor die component is mounted on a raised platform on a metal plate, with the metal can welded on top of it; providing high heat conductivity and durability. The metal case is connected to the internal device and the leads are connected to the die with bonding wires.

The TO-3 package consists of a diamond-shaped base plate with diagonals of 40.13 mm and 27.17 mm. The plate has two mounting holes on the long diagonal, with the centers spaced 30.15 mm apart. The cap attached to one side of the plate brings the total height to up to 11.43 mm. Two pins on the other side of the plate are isolated from the package by individual glass-metal seals. The metal case forms the third connection (in the case of a bipolar junction transistor this is typically the collector).

Dimensions

::figure[src="https://upload.wikimedia.org/wikipedia/commons/f/fa/Dimensions_TO-3_package_in_mm.svg" caption="Dimensions TO-3 package in mm"] ::

Variants

::figure[src="https://upload.wikimedia.org/wikipedia/commons/d/d1/Wzmacniacze.jpg" caption="CEMI]] UL1403) in a TO-3 package variant"] ::

TO-3 package variants for integrated circuits can have more than two leads. The height of the cap and the thickness of the leads differs between variants of the TO-3 package.

TO-41

::figure[src="https://upload.wikimedia.org/wikipedia/commons/6/6d/AD133.jpg" caption="AD133 transistor in an IEC C14B/B28 package, similar to TO-41 but with a third pin connected to the case (here the soldering pads have been cut off)"] ::

The two pins of the TO-41 package end in soldering pads with holes in them to make it easier to solder wires to the pins for point-to-point construction (as opposed to soldering a TO-3 package on a printed circuit board). Otherwise the TO-41 package has the same dimensions as the TO-3 package. Some variants of the TO-41 package have a third pin with a soldering pad connected to the case (e.g. AD133, AUY21). This 3-pin package was standardized by IEC as C14B/B28.

TO-204

TO-204 is intended to replace previous definitions of flange-mounted packages with a 10.92 mm pin spacing. The different outlines are now defined as variants of TO-204: TO-3 is renamed to TO-204-AA, TO-41 to TO-204-AB. A new package with a reduced maximum height of 7.62 mm is added as TO-204-AC. Two additional variants specify pins thicker than the original 1.02 mm to allow higher currents: 1.27 mm for TO-204-AD and 1.52 mm for TO-204-AE.

National standards

::data[format=table]

Standards organizationStandardDesignation forTO-3TO-41––
JEDECJEP95TO-204-AATO-204-ABTO-204-ACTO-204-AD
IECIEC 60191C14A/B18C14A/B20C14B/B18
DINDIN 418723A23B2
EIAJ / JEITAED-7500ATC-3/TB-3–TC-3A/TB-3–
British StandardsBS 3934SO-5A/SB2-2–SO-5B/SB2-2
GosstandartGOST 18472—88KT-9––KT-9B
RosstandartGOST R 57439KT-9C
Kombinat Mikroelektronik Erfurturl=https://www.bbr-server.de/bauarchivddr/archiv/tglarchiv/tgl20001bis30000/tgl26501bis27000/tgl-26713-11-jun-1988.pdftitle=TGL 26713/11: Gehäuse für Halbleiterbauelemente - Bauform Lpublisher=Verlag für Standardisierungplace=Leipzigdate=June 1988language=de
TGL 26713/11L2A2–L2A1–
::

Common components in a TO-3 package

Common voltage regulator integrated circuits:

  • LM317, voltage regulator
  • LM78xx, voltage regulator
  • LM340, voltage regulator

Common transistors:

  • 2N3055, NPN power transistor
  • MJ2955, PNP power transistor (not to be confused with a 2N2955 which is a small signal PNP transistor )
  • KD503, NPN power transistor

References

References

  1. Ward, Jack. (2007). "Motorola 2N176".
  2. Greenburg, Ralph. (2008). "Transistor Museum Oral History".
  3. Hubert Biagi. "Mounting Considerations for TO-3 Packages". Burr-Brown.
  4. "TO-41". JEDEC.
  5. (October 2010). "JEDEC Publication No. 95". JEDEC.
  6. (November 1982). "JEDEC Publication No. 95". JEDEC.
  7. (1978). "Semiconductors". [[Pro Electron]].
  8. "NPN Transistor for Powerful AF Output Stages 2N3055". Siemens.
  9. "Silicon NPN Power Transistor BU546". Telefunken.
  10. (1996). "EIAJ ED-7500A Standards for the Dimensions of Semiconductor Devices". JEITA.
  11. (1968). "Semiconductor and Photoelectric Devices". Mullard.
  12. (1974). "Mullard Technical Handbook Book 1 Part 1". Mullard.
  13. (1988). "ГОСТ 18472—88 ПРИБОРЫ ПОЛУПРОВОДНИКОВЫЕ - Основные размеры". Rosstandart.
  14. (2017). "ПРИБОРЫ ПОЛУПРОВОДНИКОВЫЕ - Основные размеры". Rosstandart.
  15. (June 1988). "TGL 26713/11: Gehäuse für Halbleiterbauelemente - Bauform L". Verlag für Standardisierung.
  16. (1991). "Kluwers Internationale Transistor Gids". Kluwer Technische Boeken B.V..
  17. "JEDEC TO-3 package specification".

::callout[type=info title="Wikipedia Source"] This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page. ::

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