Wire Wrapping 101

Wire Wrap Technique for Electronic Component Wiring

• Wire wrap is an electronic component assembly technique invented to wire telephone crossbar switches and later used for electronic circuit boards.
• The method involves interconnecting electronic components mounted on an insulating board using lengths of insulated wire wrapped around a component lead or socket pin.
• Wire wrapping can be done by hand or machine, and it allows for complex assemblies to be produced by automated equipment, yet easily repaired or modified by hand.
• Wire wrap construction produces assemblies that are more reliable than printed circuits, with connections less prone to fail due to vibration or physical stress on the base board.
• Connections in wire wrap construction are firmer and have lower electrical resistance due to cold welding of the wire to the terminal post at the corners.
• Wire wrap was used for assembly of high-frequency prototypes and small production runs, including gigahertz microwave circuits and supercomputers.
• Wire wrap construction became popular around 1960 in circuit board manufacturing, but its use has sharply declined due to the advent of surface-mount technology and the decreasing cost of professionally made PCBs.
• The modern wire wrapping technology was developed after WWII at Bell Laboratories as a means of making electrical connections in a new relay being designed for use in the Bell Telephone system.
• A "wire wrap tool" has two holes, with one for the wire and 1⁄4 in (6.4 mm) of insulated wire, and the other placed over the post for wrapping the wire.
• Automated wire-wrap machines, as manufactured by the Gardner Denver Company in the 1960s and 1970s, were capable of automatically routing, cutting, stripping, and wrapping wires onto an electronic "backplane" or "circuit board."
• Wire-wrap works well with digital circuits with few discrete components, but is less convenient for analog systems with many discrete resistors, capacitors, or other components.
• Multiple strands of wire may introduce cross-talk between circuits, of little consequence for digital circuits but a limitation for analog systems.