Flanged power transistor packing unit shell

Thier purpose
It was to make a transistor case in the 1960s for high power trasistors that needed to dissipate a lot o heat.

Overview
In electronics, TO-3 is a designation for a standardized metal semiconductor package used for transistors and some integrated circuits. The TO element stands for "transistor outline" and refers to a series of technical drawings produced by JEDEC.

The TO-3 metal can package is commonly used for power transistors, silicon-controlled rectifiers, and, occasionally, integrated circuits. TO-3 packages usually have two leads, the case being the third connection, though devices with four leads exist and more leads are possible. The TO-3 case has two mounting holes. The design originated at Motorola around 1955. The lead spacing was originally intended to allow plugging the device into a then-common tube socket.

Typical applications


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 (radio frequency) devices.

Construction
The semiconductor die component is mounted on a raised platform on a metal plate with the metal can crimped on top of it, providing high heat conductivity and durability. The 2 leads pass through the metal base plate and are sealed with glass. The metal case is connected to the internal device and the leads are connected to the die with bonding wires.

Common components that use the TO-3 package

 * 1) LM317, voltage regulator
 * 2) LM78xx, voltage regulator
 * 3) LM340, voltage regulator
 * 4) 2N3055, NPN power transistor
 * 5) 2N2955, PNP power transistor
 * 6) KD503, NPN power transistor

TO-66 power transistor packing unit shell


TO-66 is a type of semiconductor package for devices with three pins, such as transistors. The shape is similar to the TO-3package, but the size is smaller.

Overview
The TO-220 is a style of electronic component package, commonly used for discrete semiconductors as transistors and silicon-controlled rectifiers, as well as integrated circuits. The "TO" designation stands for "transistor outline". TO-220 packages have three leads. Similar packages with two, four, five or seven leads are also manufactured. A notable characteristic is a metal tab with a hole, used in mounting the case to a heatsink. Components made in TO-220 packages can dissipate more heat than those constructed in TO-92 cases.

Typical applications
The TO-220 package is a "power package" intended for power semiconductors and an example of a through-hole design rather than a surface-mount technology type of package. TO-220 packages can be mounted to a heat sink to dissipate several watts of waste heat. On a so-called "infinite heat sink", this can be 50W or more. The top of the package has a metal tab with a hole used in mounting the component to a heat sink. Thermal compound is often applied to further improve heat transfer from the package to the heatsink.

The metal tab is often connected electrically to the internal circuitry. This does not normally pose a problem when using isolated heatsinks, but an electrically-insulating pad or sheet may be required to electrically isolate the component from the heatsink if the heatsink is electrically conductive, grounded or otherwise non-isolated. Many materials may be used to electrically isolate the TO-220 package, some of which have the added benefit of high thermal conductivity.

In applications that require a heatsink, damage or destruction of the TO-220 device due to overheating may occur if the heatsink is dislodged during operation.

A TO-220 package that is heatsinked, dissipating 1W of heat, will have an internal (junction) temperature typically 2 to 5 °C higher than the package's temperature (due to the thermal resistance between the junction and the metal tab) and the metal tab of the TO-220 package will typically have a temperature of 1 to 60 °C higher than the ambient temperature, depending on the type of heatsink (if any) used.

The junction-to-case thermal resistance of a TO-220 packaged device (which typically matters less than the case-to-ambient thermal resistance), depends on the thickness and the area of the semiconductor die inside the package, typically in a range between 0.5 °C/W and 3 °C/W (according to one textbook) or 1.5 °C/W and 4 °C/W (according to another).

If more heat needs to be dissipated, devices in the also widely used TO-247 (or TO-3P) package can be selected. TO-3P has a typical junction-to-ambient (heatsink) thermal resistance of only about 40 °C/W, and its TO-3PF variant a slightly lower one. Further increase of heat dissipation capability is possible with power modules.

When a TO-220 package is used without a heatsink, the package acts as its own heatsink, and the heatsink-to-ambient thermal resistance in air for a TO-220 package is approximately 70 °C/W.

Variations
The standard TO-220 outline is defined by the JEDEC organization. There are a number of variations on this outline, such as: Sometimes the designation is followed by the number of leads, as in TO-220AB-5L for five leads, etc.
 * 1) TS7805 linear voltage regulator in a TO-220 variant package with electrically isolated tab.
 * 1) TO-220F, which has an insulated tab and body, and typically has a higher thermal resistance than the metal tab versions.
 * 2) TO-220AB
 * 3) TO-220AC

There also some vendor-specific variations such as International Rectifier's SUPER-220, which dispenses with the hole in favor of clip-mounting, thus claiming TO-247-like thermal performance in a TO-220 footprint.

Common components that use the TO-220 package

 * 1) 7805, +5 V linear voltage regulator
 * 2) 7812, +12 V linear voltage regulator
 * 3) LM317T, adjustable linear voltage regulator
 * 4) LM340, linear voltage regulator
 * 5) IRF510, N-channel MOSFET (5.6 A, 100 V)

Related packages

 * 1) TO-257 is a hermetically sealed metal package that is otherwise considered equivalent to TO-220.
 * 2) TO-220F also known as the SOT186 and SC67 is TO-220 like package, where the heatsink mounting tab has been encased in the plastic.

Soviet КТ819ГМ NPN power transistor packing unit shell


The Soviet КТ819ГМ NPN power transistor was a Soviet 2N3055 transistor copy inside in a copied TO-3 package.

Also see

 * 1) IC and transistor in line packaging
 * 2) Integrated circuits
 * 3) LM317 adjustable linear voltage regulator
 * 4) 2N3055 silicon NPN power transistor