IDC Connector: Insulation Displacement Contact

The insulation displacement contact, IDC connector provides a vey effective and reliable means of making up connectors with flat multicore ribbon cable.

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The IDC connector finds many of its uses in computer related technology. Although a variety of different forms of IDC connector are used, the most widely used one is with flat ribbon cable where multiple parallel connections are needed.

The letters IDC stand for insulation displacement contact, or it can be seen as insulation displacement connection.

The name of the connector describes the way in which it operates: it is an electrical connector designed to be connected to the conductor or conductors of an insulated cable by having specially designed connection points that cut through he simulation and make connection with the wire in the cable. This overcomes the the very time consuming process of stripping the conductors of insulation before connecting to the pins on the connector.

Example of IDC connectors in a small module

What is an IDC connector?

Insulation displacement connectors use the concept of cold welds as the basis for the technology. It was heavily influenced by research on wire-wrap and crimp connector technology where cold welds formed the concept on which these techniques depended.

Cold welding is a technique where two metals fuse when they are brought together under pressure. This occurs without the need for heat that is required for the more traditional forms of welding.

For electrical contacts the advantage is that once made, the cold weld will provide high levels of connectivity and reliability.

In terms of multi-way IDC connectors, the ribbon cable is forced down onto the contact. The contact consists flat metallic contact with an upper region where there is a slight angle to locate the wire correctly. There is then a lower U shaped region which is used to cut through the insulation and then compress the conductor so that a cold weld is formed.

IDC connector contact shape and IDC connector concept — IDC connector concept & contact shape

These connections are not only very quick to make, but also very reliable. To improve the reliability and prevent damage from flexing and strain, these connectors normally come with strain relief mechanisms that clamp the wire and hold it firmly in place.

IDC connector technology

IDC connector technology works well because metal to metal contact is generated during he assembly process. If the joint remains mechanically stable, then as time progresses additional diffusion welding can occur which can improve the joint.

However it is also possible that stress relaxation and creep of the terminal and wire can degrade the reliability. Normally the IDC terminal not only bites through the insulation, but it also applies significant pressure onto the wire so that the cold weld is formed.

The mechanical stability of the joint depends upon a number of factors including the spring properties of the terminal or connection and the loading and strain put on the wire. Both these factors can be improved by the design of the connector.

External strain relief of the cable considerably improves the long term reliability of the joint as it protects against movement at the wire terminal interface. Also the design of the IDC terminal has a major effect.

Also the wire has an effect: since the strand bundle is under compressive load, there is a tendency towards lower contact forces as the bundle relaxes in the slot due to mechanical disturbance, stress relaxation and creep. This can be affected by the number and lay or twist of the strands in the wire, the conductor top plating and the type of insulation.

If solid wire is used, this can produce a better connection, but often the wire itself is not as robust. Typically most ribbon cable is multi stranded to provide the best performance.

Types of IDC connector

Insulation displacement connection technology is used within a number of different types of connector as the technology is applicable for many areas.

Ribbon cable connectors: One of the most widely used formats with which IDC technology is used is for ribbon cable connector solutions. The ribbon cable connectors can be used for variety of different interfaces. D-type, GPIB, and very many others, but IDC connectors are probably most widely used with the header pin connectors for PCBs. These connectors typically have two rows of pins and can be used for large numbers of connections. This enables large numbers of lines on a board to be connected very easily. These connectors are used in great numbers on computer and other computer related boards.

It is important to ensure that the cables are assembled with the right orientation. Pin 1 is typically indicated on the body of the connector by a red or raised "V" mark. Some ribbon cable is multicoloured and uses the typical colour coding for the wire numbers - brown indicates one, and this is followed by red, orange, yellow, green, etc. The other main type of cable just has a line down the side of conductor number one. On the connector pin 2 is opposite pin 1, pin 3 is next to pin 1 along the length of the connector, and so on. On the cable, the wire connected to pin 2 is next to the wire connected to pin 1, and so on.
Telecommunications connectors: Some forms of telephone and network plug use insulation displacement technology. This enables reliable connections to be made during he installation of telephone appliances. The RJ or registered jack series that conforms to BS 6312 typically uses separate wires in a insulation sheath. The outer insulation is stripped and the wires are inserted or forced into the contacts using a a special termination tool. There are also some instances of Category 5 twisted pair cable being able to use this method of assembly, but for instances where set lengths can be used, Cat 5 cables can be bought relatively cheaply.

IDC connectors provide a very easy method for creating cables. Particularly those types used with computer ribbon cable provide a very fast, reliable and easy way of assembling and connecting a connector to its cable. By just aligning the wires and clamping the connector, a huge number of connections can be made very quickly.

In addition to this, IDC connector technology is generally very reliable.