View source for Lead (electronics)

{{Short description|Electrical connection consisting of a length of wire or a metal pad}}
{{about|an electrical connection|a lead waveform|phase shift|other uses|Lead (disambiguation)}}
{{Refimprove|date=April 2013}}
[[Image:Lead wires.jpg|300px|thumb|right|Several kinds of lead wires. A lead wire is a metal wire connected from the electric pole of an electronics part or an electronic component. The lead wire is a coated copper wire, a tinned copper wire or another electrically conductive wire used to connect two locations electrically.]]
In [[electronics]], a '''lead''' ({{IPAc-en|ˈ|l|iː|d}}) is an electrical connection consisting of a length of [[wire]] or a metal pad ([[surface-mount technology]]) that is designed to connect two locations [[electricity|electrically]]. Leads are used for many purposes, including: transfer of power; testing of an electrical [[Circuit (electronics)|circuit]] to see if it is working, using a test light or a [[multimeter]]; transmitting information, as when the leads from an [[Electrocardiography|electrocardiograph]] are attached to a person's body to transmit information about their heart rhythm; and sometimes to act as a [[heatsink]]. The tiny leads coming off [[Through-hole technology|through-hole]] [[electronic component]]s are also often called ''pins''{{Citation needed|date=March 2023}}; in [[ball grid array]] packages, they are in form of small spheres, and are therefore called [[Solder ball|"balls"]].

Many electrical components such as [[capacitors]], [[resistor]]s, and [[inductor]]s have only two leads, while some [[integrated circuit]]s can have several hundred or even more than a thousand for the largest [[ball grid array]] packages. Integrated circuit pins often either bend under the package body like a letter "J" (J-lead) or come out, down, and form a flat foot for securing to the board (S-lead or gull-lead). 

[[File:CSP(lead-frame) package sideview.PNG|thumb|Lead frame of a surface-mount technology package]]
Most kinds of [[integrated circuit packaging]] are made by placing a silicon chip on a '''lead frame''', [[wire bonding]] the chip to the metal leads of the lead frame, and covering the chip with plastic. The metal leads protruding from the plastic are then either "cut long" and bent to form through-hole pins, or "cut short" and bent to form surface-mount leads. Such lead frames are used for surface mount packages with leads&nbsp;– such as [[Small Outline Integrated Circuit]] [[Quad Flat Package]] &nbsp;– and for through-hole packages such as [[dual in-line package]] &nbsp;– and even for so-called [[Plastic leaded chip carrier#Leadless|"leadless"]] or "no{{nbhyph}}lead" packages<ref>Freescale. [http://www.freescale.com/webapp/sps/site/overview.jsp?code=TM_RD_PKG_LEADFRAME "Lead Frame Packaging Technology"]</ref><ref>Shinko. [http://www.shinko.co.jp/english/product/leadframe/ "IC Package Lead Frame"]</ref>&nbsp;– such as [[Quad Flat No-leads package|Quad Flat No{{nbhyph}}leads package]].

The lead frame (and therefore the pins, if any, formed from that lead frame) are occasionally made from [[Invar]] or similar alloys, due to their low [[coefficient of thermal expansion]].

==Electrical effects==
For many circuit designs it can be assumed that the leads do not contribute to the electrical effects of individual components. However, this assumption begins to break down at higher [[frequency|frequencies]] and at very small scales. These effects come from the physical construction of the leads. The leads are often metal connections that run from the rest of the circuit to the materials that each component is made of. This design results in a very small [[capacitance]] between the ends of the leads where they connect to the device and very small [[inductance]]s and [[electrical resistance|resistances]] along each lead. Because the [[electrical impedance|impedance]] of each component is a function of the frequency of the signals being passed through the device and the inductance and capacitance of the device, the leads can cause substantial variation in the properties of components in [[radio frequency]] circuits.

== See also ==
* [[Through-hole technology]]

==References==
{{reflist}}

[[Category:Electrical components]]