The Importance of Heat Management for Electronic Devices

Table of Contents

Introduction
Sheets for Small Mobile Devices
The Many Variants of the Heat Sink
Pads and Films Help Against Hot Air
Comeback for Fans
Optimum Solutions Based on Individuality

Introduction

Despite playing a vital role for humans to survive, heat can still be detrimental for electronic applications and equipment. Typically, it is the main factor responsible for malfunctions and failures of electronic equipment and applications. Nevertheless, a lot of new solutions are available for smart heat management.

The requirements with regards to heat management have changed due to gradually enhancing efficiency of components, the demand for solutions in automated manufacturing, and smaller and increasingly mobile applications. The response to heat of products and prototypes can be demonstrated right from the concept phase by Computational Fluid Dynamics (CFD) analysis. Radiation and convection of heat; resistance to heat and heat conductance of various materials; CAD data; and real environmental and installation conditions are the factors considered by CFD.

On that basis, it not only shows the causes and effects of heat loads, but also the temperature and flow distribution of a component assembly, in three-dimensional form, thereby delivering a sound decision-making basis for the most appropriate heat sink and the choice of package design.

Sheets for Small Mobile Devices

Devices such as tablets, cameras and smart phones which are small and portable are demanding ever lighter and thinner solutions for the efficient dissipation or distribution of heat. In addition, the data transfer infrastructure is incorporating increasingly intricate electronics in tight spaces: mobile devices are being used widely in medical technology; solar panels should be able to resist high heat levels; Industry 4.0 (smart manufacturing) demands increased monitoring and control possibilities; and electric-powered and hybrid vehicles require light and durable batteries.

The Pyrolytic Graphite Sheet (PGS) from Panasonic offers the ideal solution for such applications, to transport heat away from a hotspot (Figure 1) as well as to distribute heat horizontally (on the right in Figure 1). The sheet incorporates vertical and horizontal dissipation since it is a heat-conducting layer between the hotspot and heat sink and (Figure 2). A PGS sheet can dissipate the heat quickly and effectively to the cooling zone particularly where the spreader or heat sink is not directly placed at the heat source. If the sheet is mounted directly on the heat source, it discharges the heat to the external housing.

Figure 1. The PGS sheet from Panasonic dissipates heat from a hotspot and distributes it horizontally. (Source: Panasonic)

Figure 2. (Source: Panasonic)

The PGS sheet is made of light, flexible pyrolytic graphite which can be cut to shape as required. With thicknesses ranging from 10 µm to 200 µm, it can be fitted in small devices. The 2 mm bend radius enables bending of the layers to an angle of 190° more than 3,000 times. Depending on the layer thickness, the PGS sheet's thermal conductivity of 700 to 1950 W/(mK) is seven times greater than aluminum and two to five times greater than that of copper.

The efficiency of the PGS sheet is shown in Figure 3. It reveals what temperatures occur on the acrylonitrile butadiene styrene (ABS) layer when the IC is only coupled to the surface through a silicone thermal pad (type A/type B), and when a small (type A-2 / type B-2) or large (type A-1/type B-1) PGS sheet measuring 70 µm thick is placed between the PCB and the silicone layer. The temperature at the hotspot can be substantially decreased by even a small PGS sheet without the silicone thermal pad. In addition, electromagnetic interference is also shielded by the sheet. The material is stable when aged and non-sensitive to environmental influences.

Figure 3. (Source: Panasonic)

Figure 4. (Source: Panasonic)

The Many Variants of the Heat Sink

In all areas where processors are employed, the easy-to-install, light pin fin heat sinks offer an effective method of heat dissipation. Thanks to their flow-enhancing pin arrangement, they are capable of delivering high efficiency and optimum air through-flow. Besides standard products, there are also unique solutions in which the pressed-out aluminum profiles are made to customer specifications, such as using different lengths, profile cross-sections and materials; in designs as hollow-fin profiles, decor surface finishes, welded heat sinks, perforations, bores and anodized visible; and with custom packing for manual, partially or fully automated component mounting.

If the previous heat management is integrated into the development process, more information would be available and thus the technical and cost aspects can be more effectively optimized for the customer. Dimensioned profile and machining drawings, including tolerances are important requirements for optimum technical and cost specification. Also, additional 3D data is useful for complex custom profiles.

Figure 5. (Source: Assmann WSW)

Pads and Films Help Against Hot Air

Since air acts as a thermal insulator, it is necessary to avoid air gaps between heat sinks and components to attain effective heat dissipation. Heat-conducting pads are an appropriate way of equalizing any unevenness or varying component heights. Using their gap-filling properties and high thermal conductivity, heat conducting pads dissipate the power loss away from the heat source. Providing excellent compressive stress relief, they adapt optimally to the application.

The pads are silicone-free as they are made of acrylic, and can also be utilized in automotive applications. No oil leakage occurs, as in the case of increased use of thermal pastes. When stacked, the pads agglomerate to develop a mass when stacked. They can be cut more easily and be easily attached by adhesive films. As they adhere easily, the assembly can also be effortlessly dismounted.

One popular way to reduce heat resistance is to use thermal pastes. However, despite requiring complex and lengthy processing, the result is usually untidy. As a result, adhesive films are gradually being established as a complication-free variant. They are available adhering on one or two sides and are simple to process. Their ceramic filler material enables them to integrate high adhesive strength with moderate thermal conductivity. While retaining reliable performance throughout their service life, they also offer excellent shockproofing and surface coating.

Figure 6. (Source: 3M)

Comeback for Fans

Due to their susceptibility, fans are unsuitable for some applications. Although their power consumption has already been significantly lowered, it still counteracts the aims of energy efficiency. Other critical points include the space they take up, noise and durability. However when it comes to applications such as switch cabinet installations, drive systems, frequency inverters, power supplies or welding machines, fans are still unbeatable as their use boosts the fresh air throughput considerably, therefore forcing convection. The service life of fans is increasing due to enhanced bearings. For example, when compared to standard sliding bearings, the special design of an improved sliding bearing enhances the bearing's sealing, incorporates a recycling function, and also offers longer service life.

Optimum Solutions Based on Individuality

Since the choice is influenced by several factors, one-size-fits-all solution cannot answer the question regarding the best heat dissipation strategy. However, one rule does apply: The earlier in the development cycle heat management is taken into account, the wider-ranging and easier to implement the possibilities will be.

This information has been sourced, reviewed and adapted from materials provided by Rutronik Elektronische Bauelemente.

For more information on this source, please visit Rutronik Elektronische Bauelemente.

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