Page 23 - 2019 How-to-Specify E-Book
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A circumferential grounding spring can also be employed in the guide module assembly to both further improve stability and provide electrostatic discharge (ESD) protection for the plug-in module. To stabilize the PCB, stiffeners can be applied as a composite resin in the PCB itself or integrated into the chassis to reduce board flexion.
At high altitudes, electronics can be exposed to temperature extremes. As such, aerospace applications generally require PCB connectors that can function in operating temperatures extending from -55°C to 125°C, or even a wider temperature range. The effects of temperature take various forms, including:
• Relaxation of normal forces due to metal expansion and stress relief at high temperatures, especially for copper-based metals.
• Loss of structural integrity due to differing coefficients of thermal expansion between different materials, such as an aluminum shell with brass pins.
• Thermal shock that degrades the signal when the contact is exposed to extremely cold temperatures.
How connectors behave under extreme temperatures can be evaluated by several thermal performance tests, such as thermal shock tests involving hundreds of hot-cold cycles, temperature life tests (e.g., exposing connectors to 125°C for 1,000 hours), and combustion and fire-safety material testing.
Space applications typically dictate very stringent temperature and radiation requirements to evaluate how materials hold up structurally. In the vacuum of space, material selections must also consider outgassing from depressurized metal alloys, polymers, and finishes.
Humidity can accelerate corrosion in a contact interface, especially when wear from thermal cycling or vibration exposes base contact metals to fretting corrosion. Temperature and humidity tests are typically performed in the laboratory following mate/unmate cycle testing. Plastic housings are also tested to evaluate moisture absorption that can reduce insulation resistance.
PCB Treatments
PCB termination areas can degrade significantly when exposed to man-made chemicals, sunlight, saltwater, and other harsh chemicals in the natural environment. In these cases, the durability of boards and contacts can be enhanced with conformal coatings using resins, vapor phase deposition, or fluorocarbon formulations.
Simplifying PCB connector selection
Evaluating all the factors that affect PCB connectors in harsh environments is a complex task. A thorough understanding of the aspects of connector design addressed here can help simplify the specification process, but combining this knowledge with specialized tools made to navigating various design features and benefits and facilitate effective selections can make the process even easier. For example, TE Connectivity offers a High- Speed Products Developer Kit that provides designers with easy online access to product specifications, test results, and catalogs for input/output (I/O) wired, board-to-board, and radio frequency (RF) connectors, as well as cabling and fiber optics, to help them zero in on desirable features and benefits, narrow down product options, and have more confidence when selecting PCB connectors for harsh environments.
Visit TE Connectivity online.

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