New-Tech Europe | June 2017

Connectors & Cables Special Edition

Rugged design features can make micro pitch interconnects rugged by incorporating BeCu contacts, weld tabs, latches, and locks

Contact geometry, orientation, and placement in the insulator can improve signal integrity performance and life cycle

likely to take a permanent set after exposure to numerous cycles. BANDWIDTH While system speed is not a concern for most industrial EOEM designers, for some it may become a concern in the future. Industrial Ethernet is usually the maximum bandwidth requirement. Contact systems can be designed to meet both rugged and higher bandwidth requirements. One popular design incorporates BeCu to maximize spring properties, while the contact geometry and orientation in the insulator optimizes signal integrity. Specifically, the surface of the contact is milled, creating a smooth mating surface area instead of a stamped contact that mates on a cut edge. This smooth mating surface reduces the wear tracks on the contact increasing the durability and cycle life of the contact system. It also lowers insertion and withdrawal forces allowing the connectors to be zippered when unmating. The contacts are positioned in the plastic insulator so the narrow edges of the pins are parallel to each other.

applications. First is a multi-finger, heat-treated BeCu system contact. This is commonly used in 1.27 and 2.00 mm pitch systems. Although these are micro interconnects systems, the contact is designed for rugged environments. For example, a slot in the tail allows more surface area for solder adhesion. Also, connectors with micro tail slots tend to adhere to the wet solder paste prior to reflow better than flat leads. All of this increases the mechanical strength of the connector to the PCB. Also notice the slot in the transition area between the gull-wing tail and the contact. This slot, while seldom needed, is designed to prevent solder wicking. While wicking is rare in SMT applications because of the limited amount of solder, if it should occur, the slot disrupts the capillary action so the solder does not migrate into the contact area. Second is a dual wipe, phosphor bronze tuning fork design. This design is popular in rugged applications because of the contact geometry. Specifically, the length of the two mating beams (fingers) allows firm, consistent normal forces, and is less

strength, among countless other considerations. CONTACT DESIGN We will limit our brief discussion to contact base materials and design for rugged applications. Common base metals include brass, phosphor bronze, and beryllium copper. Brass is the least expensive of the three metals and has excellent electrical properties. Having said that, Samtec recommends not using brass in contacts (receptacles) in a working beam because it could fail due to low yield strengths. Phosphor bronze is stronger than brass and has better spring properties. It is excellent for contacts that have relatively few mating cycles and low contact flexure. Beryllium copper (BeCu), while more expensive than most contact materials, provides the best combination of mechanical and electrical properties. Once formed and hardened, BeCu will retain its shape under a wide variety of conditions. At Samtec, two contact systems are most popular for industrial

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