In electronics, TO-5 (Transistor Outline 5) 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 first commercial silicon transistors, the 2N696 and 2N697 from Fairchild Semiconductor, came in a TO-5 package.
The tab is located 45ð from pin 1, which is typically the emitter. The typical TO-5 package has a base diameter of , a cap diameter of , a cap height of . The pins are isolated from the package by individual glass-metal seals, or by a single resin potting. Sometimes one pin is connected directly to the metal case.
Several variants of the original TO-5 package have the same cap dimensions but differ in the number and length of the leads (wires). Somewhat incorrectly, TO-5 and TO-39 are often used in manufacturer's literature as synonyms for any package with the cap dimensions of TO-5, regardless of the number of leads, or even for any package with the diameter of TO-5, regardless of the cap height and the number of leads. Compared to TO-5, for the other variants (except TO-33 and TO-42) the minimum length of the leads was shortened from to which is sufficient for through-hole technology and leads to a cost reduction, whereas the longer leads were needed for point-to-point construction. Lead lengths of and are quite common but were not standardized separately by JEDEC. There are variants with between 2 and 12 leads. The leads are arranged in a circle with a diameter of (except TO-96, TO-97, TO-100, TO-101). Before the introduction of dual in-line packages in 1965, integrated circuits were packaged mostly in metal can packages such as the TO-5 variants with more than 3 leads.
The TO-39, TO-9, and TO-16 packages have 3 leads and differ in the shortened leads mentioned above from TO-5. Additionally, the TO-9 and TO-16 packages do not have a tab. The TO-42 package is almost identical to the TO-5 package (including the long leads) but has four stand-offs at the bottom of the base that keep the base about 0.5 mm above the circuit board. Possibly the TO-16 and TO-42 designations were not actually used.
The TO-12 and TO-33 packages have 4 leads. TO-33 has leads like TO-5 while TO-12 has leads. For transistors, the fourth wire is typically connected to the metal case as a means of electromagnetic shielding for radio frequency applications.
The TO-75 package has 6 leads (at most one of those may be omitted). The minimum angle between two adjacent leads is 60ð.
The TO-76 and TO-77 packages have 8 leads (up to three of those may be omitted). The minimum angle between two adjacent leads is 45ð. The TO-77 package differs from the TO-76 package only in that the bottom of a TO-77 package can sit directly on a circuit board whereas the TO-76 package requires a distance of up to between circuit board and package.
The TO-78, TO-79, TO-80, and TO-99 packages have 8 leads (up to three of those may be omitted). The minimum angle between two adjacent leads is 45ð. These packages differ from other variants in the height of the cap. Instead of the cap height is only for TO-78 / TO-99, for TO-79, and for TO-80. The TO-78 package differs from the TO-99 package only in that the bottom of a TO-78 package can sit directly on a circuit board whereas the TO-99 package requires a distance of up to between circuit board and package.
The TO-74 package has 10 leads (at most one of those may be omitted). The minimum angle between two adjacent leads is 36ð.
The TO-96, TO-97, and TO-100 packages have 10 leads (at most one of those may be omitted). The minimum angle between two adjacent leads is 36ð. For these packages the diameter of the circle of leads is increased from to . This allows a slightly increased chip area in a cap of unchanged diameter. TO-96 has the standard cap height of , while TO-100 and TO-97 have reduced cap heights of (like TO-78) and (like TO-79), respectively.
The TO-73 package has 12 leads (at most one of those may be omitted). The minimum angle between two adjacent leads is 30ð.
The TO-101 package has 12 leads (at most one of those may be omitted). The minimum angle between two adjacent leads is 30ð. For this package the diameter of the circle of leads is increased from to . This allows a slightly increased chip area in a cap of unchanged diameter. TO-101 has a reduced cap height of (like TO-78).
TO-205 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-205: TO-5 is renamed to TO-205-AA, TO-12 to TO-205-AB, TO-33 to TO-205-AC, TO-39 to TO-205-AD. A new package with 3 leads and a cap height of (similar to TO-78 / TO-99) is added as TO-205-AF.