How Wiring Harness Design Impacts PCB Surface Mount Reliability |
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In modern electronic systems, wiring harnesses and PCBs assembled using surface mount technology are interdependent. But most PCB designers primarily focus on the PCB layout, leaving out wiring harness design, which can ultimately be one of the critical factors that determine the reliability of the PCB. This is because a poorly designed cable assembly can introduce the following negative effects.
PCB wires with connectors
How Poor Wiring Harness Design Impacts PCB SMT Reliability
Mechanical Stress
Poorly designed wiring harnesses can exert constant flexing or pulling forces, causing stress on the surface-mounted components or solder pads. Unlike through-hole pads, SMT pads are not strong enough to handle such stresses, so the result will be cracks or component detachment over time.
The solution is to use cable clamps, connectors with locking features, adhesive mounts, or other kinds of strain relief across the joints. You can also route the wiring harnesses to reduce their flexing and pulling effects, or directional weight.
Another critical factor is using stiff or heavy connectors without mechanical support. These stress the PCB pads directly, resulting in cracks or detachment.
The solution for this issue is to pick harness connectors that are specifically designed for SMT applications with locking or other robust mounting features.
Poorly designed wiring harnesses can exert constant flexing or pulling forces, causing stress on the surface-mounted components or solder pads. Unlike through-hole pads, SMT pads are not strong enough to handle such stresses, so the result will be cracks or component detachment over time.
The solution is to use cable clamps, connectors with locking features, adhesive mounts, or other kinds of strain relief across the joints. You can also route the wiring harnesses to reduce their flexing and pulling effects, or directional weight.
Another critical factor is using stiff or heavy connectors without mechanical support. These stress the PCB pads directly, resulting in cracks or detachment.
The solution for this issue is to pick harness connectors that are specifically designed for SMT applications with locking or other robust mounting features.
A green PCB with a ribbon cable and several connectors
Noise and Interference
Wiring harnesses can introduce noise to the circuit if poorly shielded or the twisted pairs are incorrectly done. This issue is more sensitive and notable in high-frequency surface-mount PCB circuits. The solutions are simple.
- Match the impedance when transferring high-speed data between the SMT PCB and the cable harness
- Separate the power and signal wiring properly
- Use shielded cable assemblies where necessary
Hot Spots
When wiring harnesses are bundled in one spot or used in thick, low AWG sizes, they can act as heat sinks, channeling the heat unintentionally to SMT components. This situation can cause premature failure if the components are temperature-sensitive. But this can be avoided by doing thermal modeling during design and avoiding harness routing near temperature-sensitive SMT components or areas on the PCB.
Amplifying Shock and Vibrations
In applications where shock and vibrations are common, such as aerospace, automotive, and industrial, wiring harnesses can transmit vibrations from mechanical equipment and other external sources to the PCB. They can even amplify these vibrations, creating a multiplied stress effect applied to the PCB pads and SMT devices, resulting in cracking or snapping.
The best way to handle this issue is to separate the cable assemblies from the vibration areas or sources and use flexible wiring with dampening features, such as vibration isolators and grommets.
When wiring harnesses are bundled in one spot or used in thick, low AWG sizes, they can act as heat sinks, channeling the heat unintentionally to SMT components. This situation can cause premature failure if the components are temperature-sensitive. But this can be avoided by doing thermal modeling during design and avoiding harness routing near temperature-sensitive SMT components or areas on the PCB.
Amplifying Shock and Vibrations
In applications where shock and vibrations are common, such as aerospace, automotive, and industrial, wiring harnesses can transmit vibrations from mechanical equipment and other external sources to the PCB. They can even amplify these vibrations, creating a multiplied stress effect applied to the PCB pads and SMT devices, resulting in cracking or snapping.
The best way to handle this issue is to separate the cable assemblies from the vibration areas or sources and use flexible wiring with dampening features, such as vibration isolators and grommets.
Automobile wire harness repair for a PCB
How Design Collaboration Can Prevent These Issues
PCB and wiring harness designers often work separately, and in different organizations in most cases. Bringing these two teams together in an early collaboration initiative can help to align these three critical areas (mechanical, thermal, and electrical) to ensure maximum PCB and wiring harness reliability. This is what Cloom Tech does during product design to create custom wire harnesses for each project. Cloom Tech implements practices like sharing 3D CAD models of the harnesses with the PCB design team to simulate real-world scenarios and creating engineering review checkpoints to ensure the final product aligns with your project requirements fully to provide maximum reliability.
Conclusion
The link between SMT PCBs and their wiring harnesses is more than physical. You have to factor in the electrical, mechanical, and thermal behaviors, which is only possible and more effective if the design teams collaborate early. Therefore, you should consider partnering with a cable assembly manufacturer who understands this issue and implements the best design practices to ensure your SMT PCB wiring harness delivers maximum reliability and project success. Reach out to Cloom Tech if you need such a partner and learn more about their custom wiring harness assembly service.
PCB and wiring harness designers often work separately, and in different organizations in most cases. Bringing these two teams together in an early collaboration initiative can help to align these three critical areas (mechanical, thermal, and electrical) to ensure maximum PCB and wiring harness reliability. This is what Cloom Tech does during product design to create custom wire harnesses for each project. Cloom Tech implements practices like sharing 3D CAD models of the harnesses with the PCB design team to simulate real-world scenarios and creating engineering review checkpoints to ensure the final product aligns with your project requirements fully to provide maximum reliability.
Conclusion
The link between SMT PCBs and their wiring harnesses is more than physical. You have to factor in the electrical, mechanical, and thermal behaviors, which is only possible and more effective if the design teams collaborate early. Therefore, you should consider partnering with a cable assembly manufacturer who understands this issue and implements the best design practices to ensure your SMT PCB wiring harness delivers maximum reliability and project success. Reach out to Cloom Tech if you need such a partner and learn more about their custom wiring harness assembly service.