TO-18

File:BC108 family.jpg

BC108 family transistors from various manufacturers in a TO-18 package.

File:Cross section of a 2N2222 in the TO-18 package.jpg

Cross section of 2N2222 transistor in metal TO-18 package, showing connection wires between external pins and die.

File:TO-39 vs TO-18 vs TO-92 cm.jpg

Size comparison between (left to right) TO-39, TO-18, and TO-92 packages.

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

File:Botevgrad 2F2062.jpg

Phototransistor in a modified TO-18 package with lens on top.

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 (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

Standards organization	Standard	Designation for
		TO-18	TO-46	TO-71	TO-72
JEDEC	JEP95	TO-206-AA	TO-206-AB	—	TO-206-AF
IEC	IEC 60191Template:Efn	C7/B11	C10/B11		C7/B12
DIN	DIN 41876	18A3			18A4
EIAJ / JEITA	ED-7500ATemplate:Efn	TC-7/TB-8C, TC-7/TB-16C	—	—	TC-7/TB-9C
British Standards	BS 3934Template:Efn	SO-12A/SB3-6A	SO-12C/SB3-6A	SO-12A/SB8-1B	SO-12A/SB4-3
Gosstandart	GOST 18472—88	KT-1-7Template:Efn	KT-35-7Template:Efn	—	KT-1-12Template:Efn
Rosstandart	GOST R 57439
Kombinat Mikroelektronik Erfurt	TGL 11811	A3/15-3a	—	—	A4/15-4a
	TGL 26713/07	F1BA3	—	—	F1CA3

See also

• Common transistors in a TO-18 package: 2N2222, BC108 family
• Common integrated circuits in a TO-18 package: ZN414

External links

• TO-18 Package, EESemi.com