# Leads of a particular electrical component

Is lead the most common term used in electronics to indicate the number of connectible input/outputs that a component has? Are there other terms that are used interchangeably with leads?

Are there different qualifications for the type of lead it is? For example, ground would have something like one input lead but zero output leads, whereas a resistor might have two leads that could be almost interchangeable/symmetric in that they both accept incoming/outgoing directions, whereas a transistor/diode has specific leads with specific properties. In other words, is there something like a glossary or something of all the different lead types or how 'connectable areas' of a component are defined?

Technically:

• Leads (thru-hole and SMD packages that have metallic protrusions such as DIP, SOIC, SOT, and TQFP),
• Pads (SMD like QFN without metallic protrusions),
• Balls (BGA)
• Electrodes (tend to be for larger, higher voltage things, especially older equipment like vacuum tubes)

are all distinct things. But no one cares. It's all used interchangeably. "Terminal" is also another term that would cover all of the above. I tend to use "pin" or "terminal" across the board.

The specific terminal itself on a particular type of component has different names depending on the component.

For a diodes, and generally two-terminal polarized components (such as polarized capacitors or cells and batteries), it is the anode and cathode.

For BJTs and other three-terminal components of "similar NPN arrangement" such as thyristors, it's base, collector emitter.

For MOSFETs and JFETs, it's gate, source, drain.

IGBTs have gates, collectors, and emitters since they steal construction and operating traits of MOSFETs and BJTs for those respective connections.

For op amps, it's inverting input, non-inverting input, and output.

There's no glossary. You just run into it when you use the component and it's obvious what it is if you know how you're supposed to use the component. Also, the datasheet.

• "lands", "terminals", and "electrodes" are more possible names. – The Photon Feb 10 at 19:41
• @ThePhoton When I hear electrodes, I tend to think much bigger, discrete, high voltage connections like on older equipment kuje vacuum tubes. I thought landings were only ever used to refer to the PCB footprint. Are they used for the component as well? – DKNguyen Feb 10 at 19:44
• When I hear "electrode" I think battery or some other electrochemical device. – mkeith Feb 10 at 19:46
• @DKN, on a land grid array part, you might call the terminals of the part lands. – The Photon Feb 10 at 20:19
• @mkeith, if you call a diode's terminals "anode" and "cathode" you're naming them as two kinds of electrode. – The Photon Feb 10 at 20:20

To make a distinction between the electrical type of leads/pins/pads/balls there could be on an electronic device, there are:

• Inputs: Signal input, usually small voltages/currents, analog or digital.
• Outputs: Signal output, ditto. Can be further refined as "push/pull" (driven high or low, never floating), or "open drain/collector" (floating or low) and "open source/emitter" (floating or high.)
• Bi-Directional: Signal goes either way through this pin type, usually digital but could be analog also.
• Tri-State: Three states (digital only) - usually high/active, low/inactive, and a high-impedance state (off, not connected.) The state is selectable via other pin(s).
• Passive: Pin doesn't have a noteworthy function.
• Power Input: Designed for power input, sinking current from a supply.
• Power Output: Sourcing current for a load.
• Not Connected: Internally not connected to anything; mechanical only.

The pins on a resistor could be thought of as passive, as it is well-known what each does. Things get a little more complicated with something like an op-amp, as there are definite inputs and outputs, plus some power and possibly some offset pins, trim, null, etc.

• There's also open-drain/collector and open-source/emitter. And combinations open-xyz outputs are...outputs. Along with the regular push-pull output. Or I2C SDA pins which are bidirectional while also being open-drain . – DKNguyen Feb 10 at 21:46