When designing a thermal solution, one of the first decisions to make is the type of heatsink to be used. A one-piece heatsink typically consists of the heatsink base with one side containing a properly sized island or pedestal, and the other side consisting of the fins or another means to conduct the heat to where it should be dissipated. Another option is an individual heat spreader which is attached to each device separately and then thermally connected to a larger heatsink. Both methods have tradeoffs, and the decision is typically based on the number of devices that need to be contacted, the power that needs to be dissipated, and the manufacturing of the product.
Improved thermal resistance can be offered because the heatsink is a complete unit. However, when contacting multiple components, the tolerance, height, and power dissipation of each must be considered. Typically, one component is given priority, while the remaining ones have a thicker TIM to account for the worst-case tolerances of the heatsink, PCB, component height, warpage, and more. Ensuring contact across all devices can also be a challenge when manufacturing large assemblies.
When applying a heat spreader, contact with the component itself can be managed more precisely. This ensures the correct pressure is applied and reduces the thickness of the TIM 1.5, thereby lowering its thermal resistance. Although the additional TIM used between the heat spreader and the heatsink can impact heat transfer to the main heatsink, the contact area can be enlarged and adjusted to maximize heat transfer and spread to the main heatsink. This application is very beneficial when dealing with multiple device contacts to a large heatsink or when more than one device needs optimal contact. The individual heat spreader can also be used for prototyping and initial testing before the complete thermal solution is developed, with an additional off-the-shelf heatsink applied if needed.