There are many ways to attach a heat sink to a device. The most commonly used methods include thermal tapes, push pins, spring loaded screws and clips.
Double-sided thermal adhesive tapes are a quick and inexpensive way to stick a heat sink to the device. This method usually works quite well if (1) the heat sink is small and light, (2) the top surface of the device is adequately flat, and (3) a good thermal tape is used. However, for heavy heat sinks or for systems that need to pass shock and vibration test, thermal tapes are not secure enough, and the weight added to the device may even damage the device under shock or strong vibration. In addition, thermal tapes also perform as an interface material (TIM) but their thermal impedances are often much higher than other good TIMs.
Spring loaded push pins provide an easy and precise way to attach a heat sink to the device and the printed circuit board. The pressure between the heat sink and the device can be calculated and controlled by choosing the right spring. The most reliable push pins are made of spring steels and they work great at high temperature or in harsh environment. Plastic (Nylon) push pins are cost effective alternatives when the temperature in a system does not constantly exceed the glass-transition temperature (Tg) of the plastic.
Spring Loaded Screws
Spring loaded screws are the most secure way to attach a heat sink to the device and PCB. But they require additional hardware (PEM nuts, back plate, etc.) at the opposite side of the PCB and are the most expensive method. They are recommended for big and heavy heat sinks, and systems that require certification for strong vibration and shock.
Wire clips are also called z-clips. They are made of a metal wire that exerts a compression force from is middle portion. The 2 ends of the wire are locked to anchors that are either soldered or mechanically fastened to the PCB. The disadvantage of wire clips is they often require custom design for each application. So the cost can be high and lead time long.
Component clips are plastic clips (sometimes with assistance of a metal wire) that fasten heat sinks to the device (typically a BGA package) rather than the PCB. They do not require holes on the PCB but an keep-out area around the device. Similar to thermal tapes, they work well on small heat sinks but for large heat sinks, the weight of the heat sinks and the clips are transferred to the package, instead of the PCB. In some reports, engineers have found that this type of clip exerts a tensile stress, instead of compressive stress, to the solder balls and may have negative effects to the long term reliability of the BGA components.