IT Chasers

Thermal management for notebook processors

This document is written for professional system integrators building mobile PCs from industry accepted build to order laptops. It provides information and recommendations for thermal management in systems using boxed Intel® mobile processors.

It is assumed that the reader has a general knowledge of and experience with PC operation, integration, and thermal management. Integrators who follow the recommendations presented here can provide their customers with more reliable PCs and will see fewer customers returning with problems.

What is thermal management?
Laptops using mobile Intel® processors require thermal management. The term "thermal management" refers to two major elements: a cooling solution properly mounted to the processor, and effective airflow through a part of that cooling solution to evacuate heat out of the system. The ultimate goal of thermal management is to keep the processor at or below its maximum operating temperature (Case).

    

What is active cooling?
For higher power processors today, almost all laptops employ some form of an active cooling solution. This can be accomplished one of two ways. The first way is to have a heatsink attached directly to the processor. The second way would to use a Remote Heat Exchanger (RHE). A Remote Heat Exchanger, offers more flexibility in thermal design, because the actual heatsink and fan can be placed far from the processor.

A typical laptop cooling solution is far more sophisticated than that for desktop systems. With limited space, and varying laptop design, layout, and processor location, laptop cooling solutions vary greatly between laptops from different manufacturers. In all notebooks, however, the processor may use one or both of two cooling methods: passive and active.

Although the RHE design is very efficient, some notebook designs may use the RHE design together with a passive element to increase the cooling efficiency of the solution. Usually, to add a passive element, a large metal plate is attached to a part of the RHE design that allows additional heat to dissipate passively, typically from under the keyboard.

What is a heat pipe?
Heat is transferred from the processor to an attachment block, through which runs a heat pipe. A heat pipe is typically a hollow copper pipe containing a fluid and wicking material. Through a process of vaporization and recondensation, heat travels through the very efficient heat pipe to the fins of a heat exchanger (heat sink). Localized airflow then evacuates the heat to the outside air.

What is thermal interface material (TIM)?
Highly efficient cooling solutions rely heavily on proper processor installation to work. In all laptop designs, after the processor is installed, it must be attached to the laptop cooling solution. Generally, a thermal interface material (TIM) is used to provide efficient thermal exchange between the processor and attachment block. The thermal interface material type may vary depending on the laptop manufacturer. Proper installation of this thermal interface material is crucial to the success of the thermal solution.

Failure to properly install the thermal interface material could cause the processor to overheat. Follow the manufacturer's instructions carefully to ensure the thermal interface material makes 100% contact with the processor's exposed die, and with the notebook's thermal solution attachment block. Also, never touch the thermal interface material as any foreign substances (such as oils from your skin, or chemicals) can reduce the effectiveness of the thermal contact between the processor and the attachment block.

  

Do I have to replace the thermal interface material if I replace my mobile processor?
If you remove the thermal solution for a mobile processor, you should replace the thermal interface material (TIM).

Where do I get thermal interface material (TIM)?
Since each laptop has different size restrictions and thermal requirements, the thermal solution must be provided by the laptop vendor or manufacturer. Therefore, different from boxed desktop products, the thermal solution is not provided.

What is a thermal sensor?
The mobile Intel® processors incorporate an on-die diode that must be used to monitor the die temperature (junction temperature). A thermal sensor located on the motherboard, or a standalone measurement kit, may monitor the die temperature of the mobile processor for thermal management or instrumentation purposes.

What is thermal testing?
Integrators building mobile Intel® processor-based laptops should consult their manufacturer to determine the highest power processor your laptop will support. Although most laptops support throttling - a method of slowing down the processor if it exceeds its maximum operating temperature - it may cause a reduction in performance and should not be relied upon to manage the processor thermal solution.

Thermal testing may not be needed, if the processor is installed correctly and the system is designed to accommodate the power of the processor. Nonetheless, your laptop manufacturer may provide software utilities to assist in monitoring the processor temperature. Mobile Intel® processors have built in thermal diodes, and most laptops have built in circuitry to convert the diode reading into a real temperature, so processor temperatures can be monitored. Consult your laptop manufacturer for availability of a thermal monitoring utility.

Use of thermocouples to measure processor temperature may be impractical, as any attachment of thermocouples will likely compromise the performance of the thermal solution.