How IDC Termination Works

Introduction and background

The IDC termination method is commonly used in various applications. This termination technology is successfully used in a variety of industries where multi-contact mass termination is very economical. IDC can be used to achieve multi-point cable termination because the termination force is relatively small (usually a few pounds, while the crimp is hundreds of pounds). In addition, another advantage of this technology is the elimination of the stripping operation required in crimping. Therefore, in many electronic applications, this large-scale termination is often used when using multi-strand cables. In many cases, this very economical large-scale termination is made using multiple flat cables. However, discrete multi-strand cables can also be used to reduce costs, as the steps for cable stripping preparation and terminal insertion are eliminated. Such applications provide rapid assembly of high-density wiring harnesses at a lower cost. We found that IDC harnesses have a low rejection rate during assembly and excellent performance at work. The advantages of this technology are low application costs and high reliability. One disadvantage is the limitation on the geometry of the connector. The rectangular shape, usually with double rows of contacts, provides the system with the best form factor. In addition, it is required to have a wire back prevention device, because the contact surface with the terminal may not be stable enough in the case of cable vibration. In applications where large mechanical stresses occur, double slots are often required, and sometimes cable insulation clips are required.

Design concept 

The key difference between the crimping method and the IDC wiring method is the way the cable is crimped. In crimping, the pre-striped cable and terminal are severely deformed under the action of a high-pressure crimping mold, breaking through the oxide layer above it to obtain metal-to-metal contact. By applying a relatively large force to each contact, the deformation includes plastic deformation of the terminal and axial compression of the cable. Cold welding is usually produced in a strong way, and very little elastic energy is stored in the termination system. The key dimension of the crimp contact is the crimp height tolerance obtained with the crimping tool. This requires careful setting and continuous monitoring to maintain the quality of the crimp height for a long time.

In contrast, the IDC termination method requires much less force. In this case, the insulated cable is pressed into a terminal slot, which is designed to deform the cable using a shearing force that produces local plastic deformation, cut through the insulating layer, and remove the oxide. This is achieved in a single action and forms an air-tight, high-pressure contact surface between the cable and the terminal. The robust IDC system design stores a large amount of energy in the terminals because the terminals are flexible during and after termination. In IDC termination, the slot width and insertion depth of the terminals are important. In the blanking process, it is easy to control the slot width to 0.1 mil. In addition, the cable is inserted by a tool that can easily control the insertion depth. Since the insertion depth tolerance is usually a few mils, the termination quality can be checked visually. This is relatively easier to adapt to the production environment and therefore has another advantage over crimping.

Performance characteristics

The crimping effect is good because metal-to-metal contact occurs during the crimping process, and a small amount of elastic energy is stored due to the axial compression of the cable. Over time, if the crimp joint remains mechanically stable, additional diffusion welding can improve the contact surface. However, stress relaxation and creep processes in terminal / cable systems tend to reduce their mechanical stability. Therefore, depending on the mechanical design, the creep process may eventually lead to degradation. If the contact surface initially has marginal strength and is weakened by vibration and / or stress relaxation, then mechanical stability will limit its useful life.

The mechanical stability of IDC terminations depends on the elastic properties of the terminals and the load conditions of the cables. From a design perspective, this is easier to control. In addition, the cable's anti-backout device can prevent loosening of the contact between the cable and the terminal. If it is a solid core wire, IDC termination will have the same or better performance than crimping due to its inherent good mechanical stability through appropriate anti-back-out measures. This is because the elastic energy stored in the deflected terminals maintains a large pressure contact surface. Typically, for small wire gauges such as AWG26, the terminal design provides several pounds of force and several mils of elastic deflection at the contact surface. For larger wire gauges such as AWG20, the pressure can be as high as 15 to 20 pounds.

For multi-stranded wires, the mechanical stability of the core bundle plays an important role in its performance. Two factors affect its performance. First, since the core bundle is subjected to a compressive load, there is a tendency to reduce the contact force when it is relaxed in the groove due to mechanical disturbance, stress relaxation, and creep. The level of potential slack depends on the type of strand used. The number and layer (or stranding) of cores, the coating (plating) on top of the conductor, and the type of insulation play an important role in mechanical stability.

For a certain type of insulation, multi-stranded wires with no plating, more cores, fewer or no layers are the most difficult to reliably terminate; and 7-stranded wires with coatings are the simplest, often with Line the same performance. Secondly, since the contact point is composed of a limited number of cores (usually 4 of 7 strands), the conductivity between the cores affects the overall conductivity. If the cable is tinned, the overall conductivity can be optimized. It is clear that in the case of multi-stranded wires, the stress relief of a well-designed clamped cable insulation is very important. Sometimes additional (or spare) IDC terminal slots can provide the necessary mechanical stability. With proper terminal deflection (flexibility) and effective stress relief, the mechanical stability of IDC terminations for multi-strand wires can be optimized.

Cable load characteristics

Because each cable has a unique set of parameters, the load characteristics in each case must be evaluated to determine the design criteria for terminating a particular type of cable. The load characteristics of solid or stranded wires can be measured in the laboratory, using a fixed dynamometer to simulate a groove of a given guiding geometry. The measurement results are used to determine the load requirements of the terminals. Cable load characteristics can be displayed on the force curve of a given design. Note that the bevel, transition radius, and material thickness significantly affect the load characteristics of a given cable.

After this analysis, the design goal is to provide terminals that pass through a predetermined design area cable curve. Determine the design area for a given geometry by examining the contact area after the cable is inserted into the simulation device. According to the definition, the design area is the load curve area where the insulation layer is replaced and the conductor is effectively deformed to form a large pressure metal-to-metal contact. In the case of multi-strand wires, the design area usually represents the load curve area with the best mechanical stability. This area has as many good contacts as possible from the cores, and each core is not severely damaged.

Experiment method

The mechanical stability of IDC contact surfaces plays a vital role in practical performance. Therefore, vibration, mechanical and thermal shock, and temperature / humidity cycling are important factors to consider in the test. Enhancement of these factors to produce simulated practical aging laboratory tests should be given special consideration in product certification testing. During this test project, changes in termination resistance should be monitored as a primary performance characteristic. The simple failure criterion 10Rc can be used to judge its performance (10 times the minimum contact resistance of the cable and terminal contact surface).

In conclusion

When we consider the basic principles of IDC termination, it is clear that this technique can have the same good performance as a pressure contact in many applications. Moreover, this termination can reduce application costs. Such an ideal situation prompts us to seriously consider the application of IDC technology in the harness assembly operation. The opportunity to use IDC technology is available in many applications to keep its termination performance at a lower cost.