electronics The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...

, a lead () is an electrical connection consisting of a length of

wire Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample diameter 40 mm A wire is a flexible strand of metal. Wire is co ...

or a metal pad (

surface-mount technology Surface-mount technology (SMT), originally called planar mounting, is a method in which the electrical components are mounted directly onto the surface of a printed circuit board (PCB). An electrical component mounted in this manner is referre ...

) that is designed to connect two locations electrically. Leads are used for many purposes, including: transfer of power; testing of an electrical circuit to see if it is working, using a test light or a

multimeter A multimeter is a measuring instrument that can measure multiple electrical properties. A typical multimeter can measure voltage, resistance, and current, in which case it is also known as a volt-ohm-milliammeter (VOM), as the unit is equipped ...

; transmitting information, as when the leads from an electrocardiograph are attached to a person's body to transmit information about their heart rhythm; and sometimes to act as a

heatsink A heat sink (also commonly spelled heatsink) is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is dissipated away from the device, t ...

. The tiny leads coming off

through-hole In electronics, through-hole technology (also spelled "thru-hole") is a manufacturing scheme in which leads on the components are inserted through holes drilled in printed circuit boards (PCB) and soldered to pads on the opposite side, either ...

electronic component An electronic component is any basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singular form and are n ...

s are also often called ''pins''; in

ball grid array A ball grid array (BGA) is a type of surface-mount packaging (a chip carrier) used for integrated circuits. BGA packages are used to permanently mount devices such as microprocessors. A BGA can provide more interconnection pins than can be pu ...

packages, they are in form of small spheres, and are therefore called "balls". Many electrical components such as

capacitors A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...

resistor A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active e ...

s, and

inductor An inductor, also called a coil, choke, or reactor, is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. An inductor typically consists of an insulated wire wound into a ...

s have only two leads, while some

integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

s can have several hundred or even more than a thousand for the largest

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). CSP(lead-frame) package sideview

Most kinds of

integrated circuit packaging In electronics manufacturing, integrated circuit packaging is the final stage of semiconductor device fabrication, in which the block of semiconductor material is encapsulated in a supporting case that prevents physical damage and corrosion. ...

are made by placing a silicon chip on a lead frame,

wire bonding Wire bonding is the method of making interconnections between an integrated circuit (IC) or other semiconductor device and its packaging during semiconductor device fabrication. Although less common, wire bonding can be used to connect an ...

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 – such as

Small Outline Integrated Circuit A small outline integrated circuit (SOIC) is a surface-mounted integrated circuit (IC) package which occupies an area about 30–50% less than an equivalent dual in-line package (DIP), with a typical thickness being 70% less. They are general ...

Quad Flat Package A quad flat package (QFP) is a surface-mounted integrated circuit package with "gull wing" leads extending from each of the four sides. Socketing such packages is rare and through-hole mounting is not possible. Versions ranging from 32 to 304 ...

– and for through-hole packages such as

dual in-line package In microelectronics, a dual in-line package (DIP or DIL), is an electronic component package with a rectangular housing and two parallel rows of electrical connecting pins. The package may be through-hole mounted to a printed circuit board ( ...

– and even for so-called "leadless" or "nolead" packagesShinko
"IC Package Lead Frame"
/ref> – such as Quad Flat Noleads package. The lead frame (and therefore the pins, if any, formed from that lead frame) are occasionally made from

Invar Invar, also known generically as FeNi36 (64FeNi in the US), is a nickel– iron alloy notable for its uniquely low coefficient of thermal expansion (CTE or α). The name ''Invar'' comes from the word ''invariable'', referring to its relative l ...

or similar alloys, due to their low

coefficient of thermal expansion Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions. Temperature is a monotonic function of the average molecular kine ...

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

frequencies Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...

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 Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized ar ...

between the ends of the leads where they connect to the device and very small

inductance Inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. The flow of electric current creates a magnetic field around the conductor. The field strength depends on the magnitude of th ...

s and resistances along each lead. Because the 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 Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the uppe ...

circuits.

References

{{reflist Electrical components

Electrical effects

See also

References