8-Lead TO-3 Semiconductor
Transistor Package TO-3 Case style, 8-Pin
 TO-3 Metal Can, 8-Pin Flange Mount | Editor note; There are two comments that should be made about these component packages. First the component package shown is a valid package, or was at one time. That is to say, that the component package may not be in current usage, as in, no components may be offered in the particular package shown. Secondly, the component offered as an example as using this package style may or may not be in current production. In other words; the package might be valid but the component shown using the package may be out-date, obsolete or no longer in production. Although in many cases more than one component is offered as a device using a particular package. In other words as support for a particular device package fades within the industry, the package may no longer be offered as an option. If and when the devices reach end-of-life and no other component options are offered, JEDEC may pull the case number [the TO-number]. However in this instance the TO-3 style package is still widely used, but this particular 8 pin variant may not be. Finally the operational amplifier shown using this package is but one example, and many other devices could also use the same package. |
 TO-3 Metal Case | Note the location of the terminals to the mounting holes in the graphic above, some devices may have a pin attached to the metal body of the TO-3 package. This is a through-hole device, similar in size to a TO-23 package. TO-3 packages with 8 terminals are used for Operational Amplifiers, multiple transistors or FETs and other semiconductors that require more than three pins. |
The picture below shows a 2N3055 in a 3-pin TO-3 package [same size].
Flange mount. is a type of package which provides a method of readily attaching one surface of the semiconductor device to a heat sink to achieve thermal management of the case temperature. The case of this device is used as the output pin in the Op-Amp example, but not connected on the 2N3055 example. The TO-3 package style may also be called a case-mount device. |
 TO-3 Metal Case |
Case temperature is that temperature measured at a specified point on the case of a semiconductor device. While in operation the junction temperature is hotter than the case temperature. Keep in mind that not all manufacturers measure the temperature of the case at the same location on the case. So one manufacturer may appear to operate at a lower temperature when in fact the measurement is being made at a different location than specified by another manufacturer.
Normal TO-3 heatsinks are a Black Anodized Aluminum Alloy with 2 mounting holes, so the 8-lead package should work with the same heat-sinks with allowances for the extra pins, or a larger cut-out. Just be sure to specify the number of pin on the component so the heat-sink functions correctly. Also see Heat Sink Manufacturers, or Transistor Derating Guidelines.
