The system additionally integrates a unique audible “click” feature to prevent over tightening during installation, accommodates slight expansion and contraction of joint components without causing stress or damage to delicate and expensive circuitry, and allows for removal of the heat sink if necessary.
The three-piece fastening system (individual parts supplied separately) consists of Type HSCB captivating screw and Type HSL spring mated to Type HSR broaching receptacle nut or standoff. The screw and spring mount together permanently into the heat sink and the receptacle nut/standoff mounts permanently to the PC board.
After the screw and spring are captivated during the installation process, the heat sink can be attached easily to the board by simply tightening the screw into the receptacle nut/standoff. The audible “click” serves to prevent over tightening by signalling when the screw is fully engaged and installation is complete. (The screw will continue to rotate but will no longer be engaged in the threads or continue to actively tighten.)
The reliable and repeatable clamp force generated by the spring ultimately helps determine consistent and predictable clamp load on circuit board components. Screws can be installed into aluminum or steel sheets as thin as .040 in./1 mm and nuts/standoffs can be broached into boards as thin as .060 in./1.53 mm.