It can be an engineering challenge to keep circuit boards secured to heat exchangers as they experience vibrations and shock, especially in military applications. To aid designers, engineers at Pentair Technical Products, San Diego, developed Calmark Series 223 and 224 torque-limiting Card-Lok Retainers (www.calmark.com). They hold board-module assemblies tightly to the cold wall on cold-plate heat exchangers. The Card-Lok optimizes contact between thermal paths on the board and the heat sink, maximizing thermal transfer.
Card-Lok establishes a safe, yet firm clamping force of up to 350 lb. Technicians need only a standard hex wrench to attach an assembly to a heat exchanger. A screw-actuated wedge action locks assemblies into place. Five audible clicks lets technicians know the assembly is secure enough for military level-two maintenance compliance. Securing the board with the screw creates zero insertion or extraction force on the board and prevents overtightening, which may damage the board and Card-Lok. And unclamping an assembly lets the alignment spring return the Card-Lok’s wedge bodies to their start positions. This aligns the wedges for a minimal footprint in tight-tolerance situations.
The Series 223 retainers are 5.72 × 6.60 mm (0.225 × 0.260 in.) and 224 Series retainers measure 5.33 × 6.99 mm (0.210 × 0.275 in.). They come in a variety of available lengths, mounting configurations, and finishes, including some that resist corrosion and abrasion.