Page 13 - 2021 High-Reliability, Harsh Environment Connectivity eBook

Eight Considerations to Ensure You Select the Right Connectivity Solution
Whether it’s best to opt for a cable assembly based on discrete wires or an FPC will depend on the application’s electrical and mechanical requirements and operating environment. Consider these eight questions to determine the right choice for your system.
1. What current levels will the application handle?
Since FPCs rely on ultra-thin copper traces, the regular and peak current ratings for this type of cable will be lower than heavier types of cabling. Most FPCs are unlikely to exceed 1A per track, and the only way to increase their current rating would be to increase the diameter of the copper traces, which would then impinge on the flexibility of the FPC. In contrast, discrete wires are able to deliver currents that are at least three times greater than FPCs, which makes them well suited for both power delivery and data transmission applications.
2. Is keeping the overall weight of the system to a minimum a major priority?
Cable harnessing can significantly contribute to a system’s overall weight. If you are developing a high-reliability system that is battery-powered or depends on stored fuel reserves, then weight will be a key concern and specifying appropriate cabling is vital. For example, it could be advisable to deploy FPCs in an unmanned aerial vehicle (UAV) to help reduce weight, provided that the FPC can handle the application’s current levels.
3. What are the space limitations?
When considering the space requirements of a PCB-to-cable connection, there are two elements that need to be addressed. First, the height of the cable connector must exceed that of the equivalent board-mounting connector. Second, cables leaving the back of the connection vertically must have adequate space to allow for the bend radius. It may even be necessary to add padding on the opposite device, board, or enclosure to protect the bent cabling from wear during its time in the field. With FPCs, leaving the SMT connector at right angles will mitigate connection space concerns.
4. What bend radius is the cabling likely to be subjected to?
A bend radius of six to 10 times the cable’s insulation thickness is normally acceptable. Thanks to its much thinner structure, an FPC can cope with far more acute bends than discrete wire assemblies. It should be noted, though, that this only applies in one direction, along the length of the cable. For example, in a robotic arm with multiple axial joints for complex movements, a discrete-wire-based assembly that can twist and turn is very likely to be a better choice than an FPC.
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» The bend radius of a cable is determined by the structure and thickness of the wires and insulation. Learn more in Harwin’s Cable Assemblies whitepaper.
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