To complete a comprehensive thermal management strategy, an overall thermal budget that includes custom or OEM heat sink solutions depends on the physical and mechanical constraints of the system. A heat-sink solution, managed by the system-level designer, should be tailored to the design and specific system constraints. This includes understanding the inherent device capabilities for delivering heat to the surface.
By considering the system's physical, mechanical, and environmental constraints, the overall thermal budget is maintained and does not exceed the device’s maximum operating temperature. The heat sink is an integral part of the thermal management solution to maintain a safe operating temperature. As a result, the system-level designer must be aware of the following:
- For lidless packages, the nominal stiffener height can be different from the height of the die. Therefore, the heat sink must have an island to contact the die.
- Especially for lidless packages, Run thermal simulations of the system in worst-case environmental conditions using detailed thermal models, which accurately represent the device thermal performance under all boundary conditions.
- Consider the mechanical specifications of the package as well as the selection of the thermal interface between the die and the thermal management solution to ensure the lowest thermal contact resistance.
- The total thermal contact of the thermal interface material is determined based on parameters from the data sheet supplied by the thermal interface manufacturer.
- See the applied pressure recommendation section. Lower pressure runs the risk of poor thermal contact and higher pressure runs the risk of damaging the device; therefore, strict control of pressure is required. The use of a smart-torque tool is suggested when applying a heat sink to control the rate of short-term transient pressure as the thermal interface material (TIM) relaxes. Specifications from the TIM supplier should be taken into consideration.
- Consider all uncertainties in thermal modeling, including manufacturing variations from the thermal solutions (for example, fan airflow tolerance, heat pipe or vapor chamber performance tolerance, variation of the attachment of fins to heat sink base, and surface flatness).