Wire Wrap

Wire wrap is a technology used to assemble electronics. It is a method to construct circuit boards without having to make a printed circuit board. Wires can be wrapped by hand or by machine, and can be hand-modified afterwards. It was popular for large-scale manufacturing in the 60s and early 70s, and continues to be used for short runs and prototypes. It is unusual among prototyping technologies in that very complex assemblies can be produced by automated equipment, and then easily repaired or modified by hand.

Wire wrap construction can produce assemblies which are more reliable than printed circuits: connections are less prone to fail due to vibration or physical stresses on the base board, and the lack of solder precludes soldering faults such as corrosion, cold joints and dry joints. The connections themselves are firmer and have lower electrical resistance due to cold welding of the wire to the terminal post at the corners.

A correctly made wire-wrap connection is seven (7) turns of wire with 0.5–1.5 turns of insulated wire at the bottom for strain relief. The square hard-gold-plated post thus forms 28 redundant contacts. The silver-plated wire coating cold-welds to the gold. If corrosion occurs, it occurs on the outside of the wire, not on the gas-tight contact where oxygen cannot penetrate to form oxides. A correctly designed wire-wrap tool applies up to twenty tons of force per square inch on each joint.

Wire wrap was used for assembly of high frequency prototypes and small production runs, including gigahertz microwave circuits and super computers. It is unique among automated prototyping techniques in that wire lengths can be exactly controlled, and twisted pairs or magnetically shielded twisted quads can be routed together.

Wire wrap construction became popular around 1960 in circuit board manufacturing, and use has now sharply declined. Surface-mount technology has made the technique much less useful than in previous decades. Solder-less breadboards and the decreasing cost of professionally made PCBs have nearly eliminated this technology.

In telecommunications wire wrap is in common high volume use in modern communications networks for cross connects between copper wiring plant. For example, most phone lines from the outside plant go to wire wrap panels in a central office, whether used for POTS phone service, DSL or T1 lines. Typically at a main distribution frame Internal Cross Facilities Assignments and External Cross Facilities Assignments, are connected together via jumpers that are wire wrapped. Wire wrap is popular in telecommunications since it is one of the most secure ways to attach wires, and provides excellent and consistent data layer contact. Wirewrap panels are rated for high quality data services, including Cat 5 grade wiring. The principal competitor in this application is punch blocks, which are quicker but less secure.