Intel 200 User Manual

20  

 

Thermal and Mechanical Design Guidelines 

air, T

A

, and the local air velocity over the surface.  The higher the air velocity over 

the surface, and the cooler the air, the more efficient is the resulting cooling.  The 

nature of the airflow can also enhance heat transfer via convection.  Turbulent 

flow can provide improvement over laminar flow.  In the case of a heatsink, the 

surface exposed to the flow includes in particular the fin faces and the heatsink 

base. 

Active heatsinks typically incorporate a fan that helps manage the airflow through 

the heatsink.  

Passive heatsink solutions require in-depth knowledge of the airflow in the chassis.  

Typically, passive heatsinks see lower air speed.  These heatsinks are therefore 

typically larger (and heavier) than active heatsinks due to the increase in fin surface 

required to meet a required performance.  As the heatsink fin density (the number of 

fins in a given cross-section) increases, the resistance to the airflow increases: it is 

more likely that the air travels around the heatsink instead of through it, unless air 

bypass is carefully managed.  Using air-ducting techniques to manage bypass area 

can be an effective method for controlling airflow through the heatsink. 

The size of the heatsink is dictated by height restrictions for installation in a system 

and by the real estate available on the motherboard and other considerations for 

component height and placement in the area potentially impacted by the processor 

heatsink. The height of the heatsink must comply with the requirements and 

recommendations published for the motherboard form factor of interest. Designing a 

heatsink to the recommendations may preclude using it in system adhering strictly to 

the form factor requirements, while still in compliance with the form factor 

documentation. 

For the ATX/microATX form factor, it is recommended to use:  

•  The ATX motherboard keep-out footprint definition and height restrictions for 

enabling components, defined for the platforms designed with the micro-FCBGA of 

this design guide. 

•  The motherboard primary side height constraints defined in the ATX Specification 

V2.2 and the microATX Motherboard Interface Specification V1.2 found at 

The resulting space available above the motherboard is generally not entirely available 

for the heatsink. The target height of the heatsink must take into account airflow 

considerations (for fan performance for example) as well as other design 

considerations (air duct, etc.).