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Typical right-angle board-to-board SLC solution
pins with solder cups or crimp barrels are suitable for wire termination. Various sizes are available offering the ability to accommodate wires up to 16 AWG, with 9 A current handling capability. Generally speaking, it is best to operate SLCs around mid-stroke, with 2575% compression, although ‘one-time compression’ applications often benefit from maximum compression. For very low profile spring pins, 50 to 85% compression is preferred. Good design practice in less-controlled applications includes incorporating a stand-off to provide mechanical support. SLCs are able to mate with many different surfaces as a good connection is made when the plunger/piston contacts any flat or concave plated surface. Spring pins can mate with non-parallel surfaces, provided the mating force is applied axially to the piston/plunger. Lateral engagement or side-loading may cause damage.
By using spring-loaded connectors and mating with PCB pads, one side of the ‘pin-and-socket’ combination is eliminated, leading to savings in component cost and production time. Although mating with gold-plated PCB pads is most common, other options are available. A dedicated through-hole nail head pin; surface mount target pin; low-profile, gold-plated discs; or a variety of target connectors can be used. All provide a highly conductive, wear-resistant solution. Combining spring pins with targets allows different mating distances to suit any application.
Reliability is required Poor quality connections negatively impact overall system reliability, making reliability crucial to specifying SLCs. As such, when specifying SLCs, designers should review all available test data.
IEC 60512 has been the definitive standard for connector testing since 1976. It includes multiple tests to ensure that the connectors will give long-term reliability in real-world applications. Spring force, contact resistance, random, half sinus and sinusoidal vibration, rapid temperature change, dry heat, cyclic damp heat, cold test and current carrying capacity are examples of included tests.
Applications of SLCs SLC applications are only limited by the specifying designer’s imagination, although the most popular remains connectivity between two or more PCBs. As modular designs become more popular, PCB use in products is increasing. Versatile SLCs are a viable solution for parallel or perpendicular, vertical or horizontal boards and allow multiple boards to be combined easily, accommodating tolerance stack-ups due to non-parallel fixing or PCB warpage.
The larger 08xx series of power spring pins shown alongside standard 09xx series contacts
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