TO-18

In electronics, TO-18 is a designation for a style of transistor metal case. The case is more expensive than the similarly sized plastic TO-92 package. The name is from JEDEC, 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 diodes, photodiodes and LEDs 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 lasers such as those found in CD players 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 for radio frequency applications.

TO-71

The TO-71 package has 8 leads. 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 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.