The working principle of IDC termination method
Introduction and background
IDC termination method is often used in various applications. This termination technology has been successfully applied to a variety of industries where multi-contact mass termination and very economical. Multi-point cable termination can be achieved with insulation displacement connectors (IDC) because the termination force is relatively small (usually a few pounds, while crimping is hundreds of pounds). In addition, another advantage of this technology is that it eliminates the stripping operations required in crimping. Therefore, in many electronic applications, such large-scale terminations are often used when using multi-strand cables. In many cases, multiple flat cables are used for this very economical large-scale termination. However, discrete multi-strand cables can also be used to reduce costs because the steps of cable stripping preparation and terminal insertion are eliminated. This type of application provides rapid assembly of high-density wiring harnesses at a lower cost. We found that the IDC wiring harness has a low failure rate during the assembly process and excellent performance in work. The advantages of this technology are low application cost and high reliability. One disadvantage is the restriction on the connector geometry. The generally rectangular shape with double rows of contacts provides the system with the best external dimensions. In addition, it is required to have an anti-backlash device, because in the case of cable vibration, the contact surface with the terminal may not be stable enough. In applications where greater mechanical stress occurs, double grooves are often required, and sometimes cable insulation clamps are required.
Design concept
The key difference between the crimping method and the IDC wiring method is the way the cables are crimped. In crimping, the pre-stripped cables and terminals are severely deformed under the action of the high-pressure crimping mold, breaking through the oxide layer on them 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 powerful manner, and little elastic energy is stored in the termination system. The critical dimension of the crimp contact point is the tolerance of the crimp height obtained with the crimp tool (as shown in Figure 1 below). This requires careful setup and continuous monitoring to maintain high crimp quality for a long time.
In contrast, the IDC termination method requires much less force. In this case, the insulated cable is pressed into the 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 oxides. This is achieved through a single action and forms an airtight, high-pressure contact surface between the cable and the terminal. The robust IDC system design stores a large amount of energy in the terminal because the terminal is flexible during and after the termination. In IDC termination, the slot width and insertion depth of the terminal are very important. It is easy to control the groove width to 0.1 mil in the blanking process. In addition, the cable insertion is done by a tool that can simply control the insertion depth. Since the insertion depth tolerance is usually a few mils, the quality of the termination can be checked visually. This is relatively easier to adapt to the production environment, so it 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 is maintained in a mechanically stable state, additional diffusion welding can improve the contact surface. However, the stress relaxation and creep processes in the terminal/cable system tend to reduce its 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 due to vibration and/or stress relaxation, then mechanical stability will limit its service life.
The mechanical stability of IDC termination depends on the elastic properties of the terminal and the load state of the cable. From a design perspective, this is easier to control. In addition, the anti-backlash device of the cable can prevent the cable from loosening at the contact point of the terminal. If it is a solid core wire, with appropriate anti-back-out measures, IDC termination will have the same or even better performance as crimping due to its inherently better mechanical stability. This is because the elastic energy stored in the deflected terminal 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 on the contact surface. For larger wire gauges such as AWG20, the pressure can be as high as 15 to 20 pounds.
For multi-strand wires, the mechanical stability of the core bundle plays an important role in its performance. Two factors affect its performance. First, since the wire core bundle is subjected to a compressive load, when it relaxes in the groove due to mechanical disturbance, stress relaxation and creep, there will be a tendency to reduce the contact force. The potential level of slack depends on the type of strand used. The number and level of cores (or stranding), the top coating (plating) of the conductor, and the type of insulation play an important role in mechanical stability.
For a certain type of insulation, multi-strand wires with no coating, large number of cores, few or no layers are the most difficult to reliably terminate; and 7-strand wires with coating are the simplest, often with solid cores. The same performance as the line. Second, since the contact point is composed of a limited number of cores (usually 4 of the 7 strands), the conductivity between the cores affects the overall conductivity. If the cable is tinned, the overall conductivity can be optimized. Obviously, in the case of multiple strands, a well-designed clamping cable insulation is very important for stress relief. Sometimes additional (or spare) IDC terminal slots can provide the necessary mechanical stability. Through proper deflection (compliance) of the terminal and effective stress relief, the mechanical stability of the multi-strand IDC termination can be optimized.
Cable load characteristics
Since 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 specific type of cable. The load characteristics of solid or stranded wires can be measured in the laboratory, using a fixed dynamometer to simulate a slot with a given guiding geometry. The measurement result is used to determine the load requirement of the terminal. Cable load characteristics can be displayed on the force curve of a given design. Note that the bevel angle, 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 the cable curve in a predetermined design area. By inspecting the contact area after the cable is inserted into the simulation device, the design area of a given geometric shape is determined. By definition, the design area is the load curve area where the insulating layer is replaced and the conductor is effectively deformed to form a large-pressure 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 cores as possible to form good contact, and each core is not seriously damaged.
Experiment method
The mechanical stability of IDC contact surface plays a vital role in practical performance. Therefore, vibration, mechanical and thermal shock, and temperature/humidity cycles are important factors to consider in the test. The laboratory tests that enhance these factors to produce simulated practical aging should be considered in product certification testing. During this kind of test project, the change of termination resistance should be monitored as the 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 technology can have the same good performance as the crimp contact point 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 wire harness assembly operations. Many applications can provide opportunities to use IDC technology, which can maintain its termination performance at a lower cost.
IDC termination method is often used in various applications. This termination technology has been successfully applied to a variety of industries where multi-contact mass termination and very economical. Multi-point cable termination can be achieved with insulation displacement connectors (IDC) because the termination force is relatively small (usually a few pounds, while crimping is hundreds of pounds). In addition, another advantage of this technology is that it eliminates the stripping operations required in crimping. Therefore, in many electronic applications, such large-scale terminations are often used when using multi-strand cables. In many cases, multiple flat cables are used for this very economical large-scale termination. However, discrete multi-strand cables can also be used to reduce costs because the steps of cable stripping preparation and terminal insertion are eliminated. This type of application provides rapid assembly of high-density wiring harnesses at a lower cost. We found that the IDC wiring harness has a low failure rate during the assembly process and excellent performance in work. The advantages of this technology are low application cost and high reliability. One disadvantage is the restriction on the connector geometry. The generally rectangular shape with double rows of contacts provides the system with the best external dimensions. In addition, it is required to have an anti-backlash device, because in the case of cable vibration, the contact surface with the terminal may not be stable enough. In applications where greater mechanical stress occurs, double grooves are often required, and sometimes cable insulation clamps are required.
Design concept
The key difference between the crimping method and the IDC wiring method is the way the cables are crimped. In crimping, the pre-stripped cables and terminals are severely deformed under the action of the high-pressure crimping mold, breaking through the oxide layer on them 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 powerful manner, and little elastic energy is stored in the termination system. The critical dimension of the crimp contact point is the tolerance of the crimp height obtained with the crimp tool (as shown in Figure 1 below). This requires careful setup and continuous monitoring to maintain high crimp quality for a long time.
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 is maintained in a mechanically stable state, additional diffusion welding can improve the contact surface. However, the stress relaxation and creep processes in the terminal/cable system tend to reduce its 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 due to vibration and/or stress relaxation, then mechanical stability will limit its service life.
For multi-strand wires, the mechanical stability of the core bundle plays an important role in its performance. Two factors affect its performance. First, since the wire core bundle is subjected to a compressive load, when it relaxes in the groove due to mechanical disturbance, stress relaxation and creep, there will be a tendency to reduce the contact force. The potential level of slack depends on the type of strand used. The number and level of cores (or stranding), the top coating (plating) of the conductor, and the type of insulation play an important role in mechanical stability.
For a certain type of insulation, multi-strand wires with no coating, large number of cores, few or no layers are the most difficult to reliably terminate; and 7-strand wires with coating are the simplest, often with solid cores. The same performance as the line. Second, since the contact point is composed of a limited number of cores (usually 4 of the 7 strands), the conductivity between the cores affects the overall conductivity. If the cable is tinned, the overall conductivity can be optimized. Obviously, in the case of multiple strands, a well-designed clamping cable insulation is very important for stress relief. Sometimes additional (or spare) IDC terminal slots can provide the necessary mechanical stability. Through proper deflection (compliance) of the terminal and effective stress relief, the mechanical stability of the multi-strand IDC termination can be optimized.
Cable load characteristics
Since 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 specific type of cable. The load characteristics of solid or stranded wires can be measured in the laboratory, using a fixed dynamometer to simulate a slot with a given guiding geometry. The measurement result is used to determine the load requirement of the terminal. Cable load characteristics can be displayed on the force curve of a given design. Note that the bevel angle, 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 the cable curve in a predetermined design area. By inspecting the contact area after the cable is inserted into the simulation device, the design area of a given geometric shape is determined. By definition, the design area is the load curve area where the insulating layer is replaced and the conductor is effectively deformed to form a large-pressure 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 cores as possible to form good contact, and each core is not seriously damaged.
The mechanical stability of IDC contact surface plays a vital role in practical performance. Therefore, vibration, mechanical and thermal shock, and temperature/humidity cycles are important factors to consider in the test. The laboratory tests that enhance these factors to produce simulated practical aging should be considered in product certification testing. During this kind of test project, the change of termination resistance should be monitored as the 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 technology can have the same good performance as the crimp contact point 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 wire harness assembly operations. Many applications can provide opportunities to use IDC technology, which can maintain its termination performance at a lower cost.
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