Best Material Options for Custom Electrical Connectors

Electrical connectors perform simple functions: transfer power or signal (or both) into an electronic device and provide a reliable connection. The materials used in standard and custom connectors matter greatly for reliability and in determining electrical performance, but it is not always considered when designing at the systems level. Systems designers often need to balance reliability, cost, form factor, and environmental stability, and the material options presented in this article can help designers make the right decisions for connectors.

Low Cost Connectors Demand Plastics

A variety of plastics can be used for different types of electrical connectors, both for standard off-the-shelf connectors and custom connectors. Cable harness designs often require a set of custom mating connectors that can be produced from a contract manufacturer, who may draw from a portfolio of designs to create a reliable custom harness. Some of the connector body materials available include:

• Polybutylene terephthalate (PBT)

• Liquid crystal polyester (LCP)

• thermoplastic polyurethane (TPU)

• Nylon-66

• 6T or 9T plastic

• Polyamide

• Polycarbonate (PCB)

• Polyvinyl chloride (PVC)

• Acrylonitrile butadiene styrene (ABS)

• Polyurethane (PUR)

• Polysulfone (PSU)

• Polytetrafluoroethylene (PTFE)

When low cost is the main requirement for a custom connector, one of these plastics is usually the best option.

These points regarding low-cost plastic custom connectors apply at high volume, where connector bodies can be produced with injection molding. At low volume, plastic connectors are only available off-the-shelf and cannot generally be produced as custom connectors via injection molding without very high cost. However, custom mating connectors could be 3D printed from plastic filaments to accommodate off-the-shelf crimp contacts.

Rugged Connectors Demand Metals

Ruggedized connectors use metal as the primary material for the shroud/housing and pins, as well as hard plastics for internal insulation. Metals can withstand mechanical damage, high temperature, thermal stresses, pulling/twisting, and vibration. They can have very useful features like keying and retention that ensures connections are always in the right orientation and will not unexpectedly come loose.

Among metals, stainless steel is the most commonly used metal for electrical connectors due to its low cost and mechanical strength. This includes custom connectors or cable assemblies, which can be cast or machined to form connector housings. Most commonly, these are panel-mount components rather than board-mount components.

Stainless steel is an excellent rugged connector material option for many environments.

One might ask why aluminum is not used more often than stainless steel for rugged connectors given its lower cost and higher strength-to-weight ratio. One big reason is corrosion resistance; stainless steel is much more corrosion resistant than aluminum, so it is preferable in rugged systems where the connector body will be exposed to the outside environment (e.g., panel mount connectors).

Lead Tinning Options

Leads on connectors are normally coated with a metal coating to aid resilience against environmental exposure. Another very important aspect of the tinning material on the connector leads is to set the number of required mating cycles. If a connector will be plugged and unplugged repeatedly, it is desirable to have a tougher plating material; commercial plating materials can give mating cycle ratings of at least 10,000.

Some of the tinning material options available for connector leads include:

• Noble metals (tin, nickel, silver, gold, etc.)

• Tin alloys

• Nickel alloys

Ideally, the chosen plating material should provide reasonably robust corrosion resistance to any expected corrosive substances to which the connector body might be exposed, while also providing a hard surface for mating. Plating thicknesses are on the order of microns, which is typically thick enough for thousands of mating cycles and soldering directly onto component pins.

If you look at standard off-the-shelf connectors, they will also show tinning and the material should be specified in the component datasheet. For custom connectors, specialty plating service providers can offer plated leads on crimped cable assemblies, receptacles, and plug connectors.

Gold plating is more expensive but increases the allowed number of mating cycles compared to tin plating.

Shroud Material

Some electrical connections should use a shroud to provide additional protection from the elements and prevent disconnection. The materials used for connector shrouds or housings include plastics, metals, and rubber, which will vary in terms of costs and manual assembly. Some shrouds are meant for wire-to-wire connections, which will help strengthen the mating connection across a cable, while others are part of a board-mount or panel-mount housing to ensure a rugged mating connection.

The shroud materials will also determine the IP rating of the mating surfaces. Mated surfaces could appear on the device enclosure, which might be sealed with rubber to provide a high IP rating against solid and liquid ingress. This is one of the hallmark features of high-reliability connectors, and specialized connector manufacturers can assist with the design of these important components in custom connectors.

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