The demands in terms of heat management have changed as a result of steadily improving efficiency of components, smaller and increasingly mobile applications, and the need for solutions in automated manufacturing. The response to heat of products and prototypes can be demonstrated right from the concept phase by CFD (Computational Fluid Dynamics) analysis. It takes into account the resistance to heat and heat conductance of various materials, convection and radiation of heat, as well as the CAD data, and the actual installation and environmental conditions. On that basis, it depicts the causes and effects of heat loads, as well as the temperature and flow distribution of a component assembly, in three-dimensional form, so providing a sound decision-making basis for the choice of package design and the most suitable heat sink.
Sheets for small mobile devices
Small - and above all portable - devices such as smartphones, tablets and cameras are demanding ever thinner and lighter solutions for the effective dissipation or distribution of heat. The data transfer infrastructure is also incorporating increasingly complex electronics in tight spaces: Electric-powered and hybrid vehicles need light, durable batteries; Industry 4.0 (smart manufacturing) calls for ever more monitoring and control possibilities; solar panels have to withstand high heat levels; and mobile devices are increasingly being used in medical technology. For such applications, the PGS (Pyrolytic Graphite Sheet) from Panasonic offers the ideal solution, both to transport heat away from a hotspot (figure 1) and to distribute heat horizontally (on the right in figure 1). As a heat-conducting layer between the hotspot and the heat sink, the sheet combines horizontal and vertical dissipation (figure 2). Especially where the heat sink or spreader is not located directly at the heat source, a PGS sheet is able to dissipate the heat quickly and effectively to the cooling zone. If it is mounted directly on the heat source, it discharges the heat to the external housing.
The PGS sheet is made of a light, flexible pyrolytic graphite which can be cut to shape as required. With thicknesses from 10µm to 200µm, it also fits in small devices. The 2mm bend radius allows the layers to be bent more than 3,000 times to an angle of 190°. Depending on the layer thickness, the PGS sheet's thermal conductivity of 700 to 1950W/(mK) is two to five times higher than that of copper, and seven times than of aluminum.
Figure 3 demonstrates the efficacy of the PGS sheet. It shows what temperatures occur on the ABS (acrylonitrile butadiene styrene) layer when the IC is only connected to the surface by a silicone thermal pad (type A / type B), and when a large (type A-1 / type B-1) or small (type A-2 / type B-2) PGS sheet 70µm thick is placed between the silicone layer and the PCB. Even a small PGS sheet with no silicone thermal pad substantially reduces the temperature at the hotspot. It additionally shields electromagnetic interference. The material is non-sensitive to environmental influences, and stable when aged.
The many variants of the heat sink
The light, easy-to-install pin fin heat sinks provide an effective method of heat dissipation in all areas where processors are used. Thanks to their flow-enhancing pin arrangement, they deliver high efficiency and optimum air through-flow. In addition to standard products, there are also special solutions in which the pressed-out aluminum profiles are machined to customer specifications, such as using various materials, profile cross-sections and lengths; in designs as hollow-fin profiles, perforations, bores, welded heat sinks, anodized visible and decor surface finishes; and with custom packing for manual, partially or fully automated component mounting. The earlier heat management is integrated into the development process, and the more information is available, the more effectively technical and cost aspects can be optimized for the customer. Essential necessities for optimum technical specification and costing are dimensioned profile and machining drawings, including tolerances. For complex custom profiles, additional 3D data is also helpful.
Pads and films help against hot air
In order to achieve effective heat dissipation, air gaps between components and heat sinks must be avoided, because air acts as a thermal insulator. Heat-conducting pads are a suitable means of equalizing any unevenness or differing component heights. With their high thermal conductivity and gap-filling properties, they dissipate the power loss away from the heat source. They provide outstanding compressive stress relief, and adapt optimally to the application. The pads are made of acrylic, so they are silicone-free, and can also be used in automotive applications. There is no oil leakage, as can occur if thermal pastes are used excessively. Also, the pads agglomerate to form a mass when stacked. They can be more easily cut, and are easy to affix by adhesive films. As they adhere easily, the assembly can also be conveniently dismounted.
Thermal pastes are a popular way of reducing heat resistance. They do, however, require lengthy and complex processing, and the result is often still untidy. Consequently, adhesive films are becoming established as a complication-free variant. They are available adhering on one or two sides, and are easy to process. Thanks to their ceramic filler material, they combine moderate thermal conductivity with high adhesive strength. They also provide outstanding surface coating and shockproofing, while retaining consistent performance throughout their service life.
Comeback for fans
Fans are unsuitable for some applications because of their susceptibility. Their power consumption counteracts the aims of energy efficiency, even though it has already been significantly reduced. The space they take up, noise and durability are other critical points. But fans are still unbeaten when it comes to applications such as drive systems, frequency inverters, switch cabinet installations, power supplies or welding machines, as their use greatly boosts the fresh air throughput, thereby forcing convection. Improved bearings are extending the service life of fans. For example, the special design of an optimized sliding bearing enhances the bearing's sealing, incorporates a recycling function, and provides longer service life than conventional sliding bearings.
Optimum solutions based on individuality
The question as to the best heat dissipation strategy cannot be answered with a one-size-fits-all solution, because numerous factors influence the choice. One rule does apply though: The earlier in the development cycle heat management is considered, the wider-ranging and easier to implement the possibilities will be.