In electronics, TO-3 is a designation for a standardized metal

semiconductor package A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...

used for power semiconductors, including

transistor upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch e ...

silicon controlled rectifier A silicon controlled rectifier or semiconductor controlled rectifier is a four-layer solid-state current-controlling device. The name "silicon controlled rectifier" is General Electric's trade name for a type of thyristor. The principle of four ...

s, and,

integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

s. ''TO'' stands for "Transistor Outline" and relates to a series of technical drawings produced by

JEDEC The JEDEC Solid State Technology Association is an independent semiconductor engineering trade organization and standardization body headquartered in Arlington County, Virginia, United States. JEDEC has over 300 members, including some of the w ...

. The TO-3 case has a flat surface which can be attached to a

heatsink A heat sink (also commonly spelled heatsink) is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is dissipated away from the device, the ...

, normally via a thermally conductive but electrically insulating washer. The design originated at

Motorola Motorola, Inc. () was an American Multinational corporation, multinational telecommunications company based in Schaumburg, Illinois, United States. After having lost $4.3 billion from 2007 to 2009, the company split into two independent p ...

around 1955 from a group headed by Dr. Virgil E. Bottom. 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 Tube sockets are electrical sockets into which vacuum tubes (electronic valves) can be plugged, holding them in place and providing terminals, which can be soldered into the circuit, for each of the pins. Sockets are designed to allow tubes to b ...

Typical applications

The metal package can be attached to a heat sink, making it suitable for devices dissipating several watts of heat.

Thermal compound Thermal paste (also called thermal compound, thermal grease, thermal interface material (TIM), thermal gel, heat paste, heat sink compound, heat sink paste or CPU grease) is a thermally conductive (but usually electrically insulating) chemi ...

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 Micas ( ) are a group of silicate minerals whose outstanding physical characteristic is that individual mica crystals can easily be split into extremely thin elastic plates. This characteristic is described as perfect basal cleavage. Mica is ...

or other materials with good

thermal conductivity The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...

. 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 seal A hermetic seal is any type of sealing that makes a given object airtight (preventing the passage of air, oxygen, or other gases). The term originally applied to airtight glass containers, but as technology advanced it applied to a larger categor ...

s 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

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 and . The plate has two mounting holes on the long diagonal, with the centers spaced apart. The cap attached to one side of the plate brings the total height to up to . 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 A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor, uses only one kind of charge carrier. A bipolar ...

this is typically the collector).

Variants

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

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 Point-to-point construction is a non-automated method of construction of electronics Electronic circuit, circuits widely used before the use of printed circuit boards (PCBs) and automated assembly gradually became widespread following their intr ...

(as opposed to soldering a TO-3 package on a

printed circuit board A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in Electrical engineering, electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a L ...

). 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 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 is added as TO-204-AC. Two additional variants specify pins thicker than the original to allow higher currents: for TO-204-AD and for TO-204-AE.

National standards

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Rosstandart Federal Technical Regulation and Metrology Agency (Rosstandart) (russian: Федеральное агентство по техническому регулированию и метрологии (Росстандарт)) is the Russian federal ...

GOST GOST (russian: ГОСТ) refers to a set of International standard, international Technical standard, technical Standardization, standards maintained by the ''Euro-Asian Council for Standardization, Metrology and Certification (EASC)'', a region ...

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Kombinat Mikroelektronik Erfurt VEB Kombinat Mikroelektronik Erfurt was an important manufacturer of active electronic components in East Germany. It should not be confused with the more well-known VEB Kombinat Robotron Dresden which used integrated circuits from Kombinat M ...

, TGL 11811 , Eeb , – , Eea , – , - , TGL 26713/11 , L2A2 , – , L2A1 , –

Common components in a TO-3 package

Common voltage regulator integrated circuits: *

LM317 The LM317 is a popular adjustable positive linear voltage regulator. It was designed by Bob Dobkin in 1976 while he worked at National Semiconductor. The LM337 is the negative complement to the LM317, which regulates voltages below a reference. ...

, 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 The 2N3055 is a silicon NPN power transistor intended for general purpose applications. It was introduced in the early 1960s by RCA using a hometaxial power transistor process, transitioned to an epitaxial base in the mid-1970s. Its numbering fo ...

, NPN power transistor

References

External links

TO-3
standard from

TO-3 package
from EESemi.com
Hermetic packages
from

National Semiconductor National Semiconductor was an American semiconductor manufacturer which specialized in analog devices and subsystems, formerly with headquarters in Santa Clara, California. The company produced power management integrated circuits, display drive ...

{{DEFAULTSORT:TO-003 Semiconductor packages