The
TO-3
or TO3
is
a
type of 'metal can' package that is capable of high-power dissipation
commonly used by power transistors, SCR's and other high-power
semiconductor devices.
The TO-3 is made entirely of metal, with the microchip mounted on its
metal can base and then covered with a metal cap.
TO-3 packages are designed to accommodate large heat sinks to increase
their power handling capability. If necessary, the heat sink may be
electrically isolated from the TO-3 package using mica or ceramic
insulator pads that are inserted between the TO-3 body and the heat
sink.
A typical power transistor packaged in
a TO-3 package has two protruding terminals (one for the base and the
other for the emitter), with the collector using the TO-3's body itself
as its terminal for direct thermal conduction to the heat sink. Although
most TO-3 packages have 2 or 3 protruding terminals only, TO-3's with
higher lead counts do exist.
Advantages of the TO-3 package include:
1) excellent power handling capability, 2) high durability, 3) ease of
mounting, and 4) hermetic sealing that protects the chip from
environmental factors. Disadvantages of the TO-3 package include
its relatively higher cost and larger size than other packages.
Table 1. Properties of
a Typical TO-3
|
Base Size
(Length x
Width x Thickness) |
Cap
Diameter |
Cap
Height |
Lead
Length |
Lead
Pitch |
|
39.3 mm x
26.6 mm x 1.7 mm |
22.2 mm |
5.7 mm |
11.7 mm |
10.9 mm |
