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Diode Package Styles

A diode is an electronic component that acts like a plumber's flapper valve, permitting electrical current flow in only one direction. Diodes have two leads or terminals, and come in a variety of package styles, depending on their voltage and current ratings and whether they are surface mount or leaded devices. The more current a diode carries, the larger its package. JEDEC, the Joint Electron Devices Engineering Council, has standardized diode package styles into roughly two dozen types.

Surface Mount
- Surface mount diodes consist of a rectangular body with a stubby terminal on two sides. The terminals serve as connection points between a circuit's wiring and the diode itself. Though their small size makes them challenging to assemble by hand, surface mount components are ideal for mass production by machine. They are smaller, lighter and less expensive than components with leads, and allow more circuitry to fit a given device. Examples of JEDEC standard numbers for surface mount diode packages include DO-219AB and SOD-523.
Axial Lead
- Diodes with axial leads have a cylindrical body slightly smaller than a grain of rice. The body may be made of hard epoxy resin or glass, depending on the device. A wire lead protrudes from the cylinder's top and bottom sides, following the component's long axis. To place a diode in a circuit, a technician bends the leads 90 degrees relative to the body, so they both point down, then inserts the leads into holes in a circuit board. He solders the leads to the copper foil on the board, then clips the excess lead material flush to the board's bottom side. This makes a sturdy, reliable connection. Standard axial lead diode case style numbers include the JEDEC DO-35 and DO-41.
Stud
- Diodes that carry more than a few amps of current or 200 volts have more rugged case styles, such as the JEDEC DO-8 or DO-203. These devices produce more heat than diodes with lower ratings. The stud-mount package has a metal body that conducts heat away from the part and to a heat sink or cooling fan. Instead of soldering to a circuit board, these diodes mount to a metal panel with standard-sized nuts and other hardware. This allows larger currents to flow through the diode at low electrical resistance.
Array
- In many cases, a circuit will use more than one diode of a given type. Electronic designs can save cost and space if they use a diode array that contains several diodes in the same package. A three-terminal case, for example, contains two diodes that share a common lead. An eight-pin case can hold four independent diodes or up to 12 diodes that share common pins. JEDEC's designation for an eight-pin package is the SO-8.

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