Heat sinks are designed in a way to have a large surface area to maximize the contact with the air or fluid  medium, such as air or liquid coolant to absorb heat and direct it away from the device. Aluminum alloys are preferred to be used in constructing heat sinks. This is because Aluminum is lighter and cheaper than copper

Dimensions

Specifications and Features: 

1. Matching With The CM4 On Size And Mounting Holes
2. Fast Heat Dissipation
3.  Corrosion / Oxidation Resisting
4. Dedicated Aluminum Heatsink
5. Using With CM4 Base Board
6. Compatible with: Raspberry Pi
7. Color: Black
8. Simple Version Heatsink, Easy to Instal