Table of Content:
Introduction
Notebook Thermal Management
Processor Installation
Thermal Testing
Introduction
This document is written for professional system integrators building Mobile PCs from industry-accepted build-to-order notebooks. It provides information and recommendations for thermal management in systems using the boxed Intel® Celeron® M processor.
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.
Notebook Thermal Management
Notebooks using Intel Celeron M processors all 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 from the system. The ultimate goal of thermal management is to keep the processor at or below its maximum junction temperature (Tj) while operating at the Thermal Design Power (TDP). The Celeron M processor's Tj is specified in the processor datasheet and is the hottest location on the die. The Thermal Monitor is a new feature only in the Celeron M processor and is used to indicate when the maximum Tj has been reached.
A typical notebook cooling solution is far more sophisticated than that for desktop systems. With limited space, and varying notebook design, layout, and processor location, notebook cooling solutions vary greatly between notebooks from different manufacturers. In all notebooks, however, the processor may use one or both of two cooling methods: passive and active.
Thermal solutions using a heat exchanger have been modified for better performance. Some of the changes include higher conductive material, more surface area, improved mechanical attach, higher performance fans, and thermal interface material changes. These designs will vary with the different manufacturer's notebooks and models.
A Remote Heat Exchanger, or RHE, offers flexibility in thermal design, because the actual heatsink and fan can be placed far from the processor. Figure 1 shows the RHE design concept.
Figure 1: Typical Remote Heat Exchanger Design
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 re-condensation, 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.
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. Figure 2 shows an example of an actual thermal solution using a remote heat exchanger.
Figure 2: Typical Thermal Solution Design
Highly efficient cooling solutions rely heavily on proper processor installation to work. In all notebook designs, after the processor is installed, it must be attached to the notebook cooling solution. Generally, a thermal interface material is used to provide efficient thermal exchange between the processor and attachment block. The thermal interface material type may vary depending on the notebook 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.
In addition, if a notebook uses an additional passive thermal solution, such as a plate underneath the keyboard, this passive solution must be re-attached carefully. Systems that utilize an additional passive thermal system rely on it to meet the cooling requirements of the entire system.
Integrators building Intel® Celeron® M processor based notebooks should consult their manufacturer to determine the highest power processor the notebook will support. Although most notebooks 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.
The Intel Celeron M processor has built-in power management and features for processor thermal monitoring. It incorporates two methods of monitoring die temperature, the Thermal Monitor and the thermal diode. The Thermal Monitor must be used to determine when the maximum specified processor junction temperature (Tj) has been reached. The second method, the thermal diode, can be read by an off-die A/D converter (a thermal sensor) located on the motherboard, or a standalone measurement kit. The thermal diode may be used to monitor the die temperature of the processor for thermal mangement or instrumentation purpose but cannot be used to indicate if the maximum junction temperature of the processor has been reached. The output of the thermal sensor connected to the thermal diode does not reflect the temperature of the hottest location on the die (Tj). The offset between the hottest location of the die (Thermal Monitor) may be characterized using the Thermal Monitor's Automatic mode activiation of thermal control circuit. This temperature offset must be taken into account when using the processor thermal diode to implement power management events.
Thermal Monitor is a feature available on the Intel Celeron M processor that allows the processor and system thermal solutions to be designed much closer to the power envelopes of real applications, instead of being designed to the much higher maximum processor power envelopes. Thermal Monitor controls the processor temperature by modulating (starting and stopping) the processor core clocks. Automatic and On-Demand modes are used to activate the thermal control circuit (TCC). When automatic mode is enabled, the TCC will activate only when the interanl die temperature is very near the temperature limits of the processor.
Use of thermocouples to measure processor temperature may be impractical, as any attachment of thermocouples will likely compromise the performance of the thermal solution.
For more information on the Celeron M processor thermal specifications, refer to the Celeron M ProcessorDatasheets.
