Cross section of a 2N2222 in the TO-18 package

electronics Electronics is a scientific and engineering discipline that studies and applies the principles of physics to design, create, and operate devices that manipulate electrons and other Electric charge, electrically charged particles. It is a subfield ...

, TO-18 is a designation for a style of

transistor A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...

metal case. The case is more expensive than the similarly sized plastic

TO-92 The TO-92 is a widely used style of semiconductor package mainly used for transistors. The case is often made of epoxy or plastic, and offers compact size at a very low cost. History and origin The JEDEC TO-92 descriptor is derived from the ori ...

package. The name is from

JEDEC The Joint Electron Device Engineering Council (JEDEC) Solid State Technology Association is a consortium of the semiconductor industry headquartered in Arlington County, Virginia, Arlington, United States. It has over 300 members and is focused ...

, signifying ''Transistor Outline Package, Case Style 18''.

Construction and orientation

The typical TO-18 metal can package has a base diameter of , a cap diameter of , a cap height of . The tab is located 45° from pin 1, which is typically the emitter. The lead diameter is nominally . The leads are arranged in a circle with a diameter of . The minimum length of the leads is . Different manufacturers have different tolerances, and the actual form factor may vary slightly, depending on function.

Uses and variants

The 3-lead TO-18 is used for transistors and other devices using no more than three leads. Variants for

diode A diode is a two-Terminal (electronics), terminal electronic component that conducts electric current primarily in One-way traffic, one direction (asymmetric electrical conductance, conductance). It has low (ideally zero) Electrical resistance ...

photodiode A photodiode is a semiconductor diode sensitive to photon radiation, such as visible light, infrared or ultraviolet radiation, X-rays and gamma rays. It produces an electrical current when it absorbs photons. This can be used for detection and me ...

s and

LED A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corresp ...

s may have only two leads. Light-sensitive or light-emitting devices have a transparent window, lens, or parabolic reflectors in the top of the case rather than a sealed, flat top. For example,

diode laser The laser diode chip removed and placed on the eye of a needle for scale A laser diode (LD, also injection laser diode or ILD or semiconductor laser or diode laser) is a semiconductor device similar to a light-emitting diode in which a diode p ...

s such as those found in

CD players A CD player is an electronic device that plays audio compact discs, which are a digital optical disc data storage format. CD players were first sold to consumers in 1982. CDs typically contain recordings of audio material such as music or audi ...

may be packaged in TO-18 cases with a lens. There are variants with between 2 and 8 leads.

TO-46 / TO-52

The TO-46 and TO-52 packages have 3 leads. These packages differ from all other variants in the height of the cap. Instead of the cap height is only for TO-52 and for TO-46.

TO-72

The package with 4 leads but otherwise with dimensions identical to TO-18, is standardized as TO-72. The fourth wire is typically connected to the metal case as a means of

electromagnetic shielding In electrical engineering, electromagnetic shielding is the practice of reducing or redirecting the electromagnetic field (EMF) in a space with barriers made of conductive or magnetic materials. It is typically applied to enclosures, for isol ...

for

radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the u ...

applications.

TO-71

The TO-71 package has 8 leads (up to three of those may be omitted). The minimum angle between two adjacent leads is 45°.

TO-206

TO-206 is intended to replace previous definitions of packages with leads arranged in a circle with a diameter of . The different outlines are now defined as variants of TO-206: TO-18 is renamed to TO-206-AA, TO-46 to TO-206-AB, TO-52 to TO-206-AC, TO-72 to TO-206-AF. A new package with 3 leads and a cap height of (i.e. smaller than TO-46) is added as TO-206-AD. TO-206-AE does not require a minimum diameter of the leads but is otherwise identical to TO-18. The somewhat unrelated TO-58 package is included as TO-206-AG.

National standards

References

External links

TO-18 Package
EESemi.com {{DEFAULTSORT:TO-018 Semiconductor packages