TO-3 Package

                

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

   

Figure 1.  Example of a TO-3 Package

      

See more TO Package Types

See more IC Package Types

   

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