SOT-23 Package
SOT-23 Body style Transistor or FET SMD package
SOT-23 Package Drawing and Package Dimensions
The SOT-23 package is a 3-terminal plastic surface mount component.
A similar package style is the TO-236AA SMD Transistor.
 SOT-23 Package Drawing |
Case temperature. Because the SOT-23 is a Surface Mount Device [SMD] heat transfer will also be conducted via the component leads. There are no leads to shorten to increase heat conduction as in a thru-hole component. The TO-236 has to be mounted to a Printed Circuit Board [PCB] so the lands or PWB pads are used to transfer heat. For best results use the largest pads possible while keeping the required spacing between pads. |
The weigh of the copper [copper thickness] is of marginal help with 3oz copper providing the same heat transfer as 1oz copper. However the surface area of the PCB pads makes all the difference in conducting heat. The larger the pad surface area, the lower the thermal resistance. Heat conduction increases as thermal resistance decreases. |  SOT-23 Package Drawing |
 SOT-23 | The text above indicates that this package is used by either transistors or FETs but almost any two or three terminal semiconductor could use this package: Thyristors, IGBTs and so on. Because of the package size, the SOT-23 is a low current device. Additional SOT23 Package Variations. |
SOT23-MO
| An additional version of the SOT23 package is the SOT23-MO package style. This variation is a 6-pin package, with three pins on either side of the plastic body. No physical dimensions are provided because there are a number of variations. For example the physical width of the plastic body is 1.75mm for a SOT23-MO-178 package, or 1.45mm for a SOT23-MO-203 package [max dimension]. The length could also vary between package versions; for example the MO-178 package has a length of 3.05mm, while the MO-203 package has a length of 2.15mm. |  SOT-23-MO-178 Package Drawing |
When holding one transistor per package it's common for 4 of the pins to be dedicated to the collector, allowing 4 pads on the printed wiring board to dissipate heat. Of course the remaining two terminals are used for the Base and Emitter of the transistor.
The SOT package used with transistors is similar to the SOP package used with digital ICs. Although the dimensions and number of pins changes with the semiconductor function used within the device and number of terminals required.
