Captive screws dissipate heat in electronics

Dean Palmer reports on a new range of captive fasteners that offer maximum heat dissipation in electronic heat sink applications

A new range of captive fasteners has been launched that are designed specifically for electronic heat sink applications, offering consistent, high load mechanical fastening that maximises thermal conductivity regardless of chip thermal expansion, shock and vibration. According to fastener manufacturer Southco, the company's '5T Heat Sink Series' captive screws provide thermal and mechanical engineers involved in printed circuit board (PCB) applications with "several distinct advantages beyond the capabilities of previous heat sink fastening methods". First, the design provides a consistent set preload - up to a maximum of 22N per screw - to maximise surface contact and thermal conductivity throughout the range of chip expansion. This means a smaller heat sink can be used, conserving space and cutting costs. Each screw incorporates a positive stop to set the preload, which helps prevent damage to the PCB. Designed to mount at the outer edges of the heat sink, the captive screws also cause minimal or zero interference with heat sink fins and do not compromise their function. The hardened steel captive screws with stainless steel springs deliver durable performance to withstand drop tests and vibration testing. And, because the screws are captivated into the heat sink panel itself and feature a self-contained spring, there are no loose hardware to short-circuit or damage the PCB. The spring-loaded design also compensates for inconsistent chip and interface material thickness. Southco says the screws come with a standard #2 Phillips/slot head style. A flare-in installation style makes it easier to captivate screws within the heat sink material. The heat sink screws are free of hexavalent chrome and in salt spray corrosion testing, the screws exceeded 144 hours of treatment. Multiple screw thread sizes and lengths are available. Southco is active in many other industries. As well as supplying the marine and automotive industries, the company has also launched a fully compliant ATCA faceplate mounting hardware solution to satisfy industry standards for telecommunications computer applications. The components - including ejector handles, safety ground pins and captive retention screws - meet all the requirements of the Advanced Telecom Computing Architecture (ATCA) PICMG 3.0 R2.0 standards for faceplate mounting and fastening. These products provide telecoms companies and telecoms equipment manufacturers with a complete and convenient solution, the ability to customise components to suit unique user specifications and the advantages of bundled pricing options. The Southco ejector handle for the standard ATCA application has an ergonomic design with ample leverage for ease of use. It has the required 500N load capacity for durable performance and a secondary catch for reliable engagement. The catch firmly locks into the faceplate, where it operates a micro switch that permits hot-swapping. The ejector handle's aesthetically pleasing design takes up minimal space on the faceplate of the assembly and can withstand more than 250 inject/eject cycles as specified in the ATCA standard. The safety ground pins, which are used to ensure accurate alignment of the board/faceplate and to provide a grounding connection, have a bullet-tip design and a very smooth finish to allow for easy engagement.