leads

In electronics, a lead is an electrical connection consisting of a length of wire or metal pad (SMD) that comes from a device. Leads are used for physical support, to transfer power, to probe circuits (see multimeter), to transmit information, and sometimes as a heatsink. The tiny leads coming off through-hole components are also often called pins. Many electrical components such as capacitors, resistors, and inductors have only two leads where some integrated circuits (ICs) can have several hundred leads to more than a thousand for the largest BGA devices. IC 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). Most kinds of integrated circuit packaging’are made by placing the silicon chip on a lead frame; then wire bonding the chip to the metal leads of that lead frame; and then 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 (SOIC), Quad Flat Package (QFP), etc. — and for through-hole packages such as dual in-line package (DIP) etc. — and even for so-called “leadless” or “no-lead” packages’such as quad-flat no-leads package (QFN), etc. The lead frame (and therefore the pins, if any, formed from that lead frame) are occasionally made from FeNi42, a kind of Invar.