About Thermal Design

Goals in the design of electronic equipment include miniaturization, efficiency improvements, EMC (electromagnetic compatibility), and the like, but in recent years there has been increasing attention paid to thermal issues, and thermal design has emerged as a new problem area. Heat is related to the performance, reliability, and safety of components and equipment, and so has always been one important issue for study. But the demands made of electronic equipment have changed lately, and it has become necessary to take a new look at established practices. Hence Tech Web here considers thermal design.

In this discussion of “Thermal Design of Semiconductor Components in Electronic Equipment”, we address thermal design that basically assumes semiconductor components such as ICs and transistors that are used in electronic equipment.

About Thermal Design

In semiconductor components, an absolute maximum temperature rating Tjmax of the junction temperature, which is the temperature of a chip in its package, is stipulated. In the design stage, heat generation and ambient temperatures must be studied so as to ensure that the component does not exceed Tjmax. Hence thermal calculations are performed for all semiconductor components that are to be used to determine whether or not Tjmax will be exceeded; if it is found that temperatures will rise above Tjmax, measures must be taken to reduce losses or to reconsider heat dissipation, so that the temperature stays within the maximum rating Tjmax. This is thermal design in a nutshell.

Of course, in addition to semiconductor components, various other devices such as capacitors, resistors, motors, and the like are used in electronic equipment, and each of these has absolute maximum ratings relating to temperatures and power losses. Thus in actual practice, the design must ensure that maximum ratings for temperature are not exceeded for all of the components used in any equipment unit.

The Importance of Thorough Thermal Design in the Design Stage

If comprehensive thermal design is not performed in the design stage and measures related to heat not taken, problems originating in heat issues may occur in the product prototyping stage or, in some cases, may be discovered prior to mass production. While not an observation that is limited to heat, it must be remembered that the closer to mass production when a countermeasure is implemented, the greater the time and costs entailed, and if product shipments are delayed, major problems leading to lost business opportunities may occur. In the worst case, problems may occur in the marketplace, possibly culminating in recalls and loss of trust.

Heat-related problems are not pleasant to contemplate, but there is the real possibility of issues ranging from smoke emission to flames and even to fires that could threaten human lives. The essential fact is that thermal design is vitally important. Hence sound thermal design beginning from the initial stages is indispensable.

The Mounting Importance of Thermal Design

In recent years, it has come to be taken for granted that electronic equipment must be more compact and capable of ever higher performance. To this end, integration levels have continued to advance. More specifically, the number of components used has increased, mounting densities on circuit boards are also rising, and housings are made as small as possible. As a consequence, heat generation densities are also rising sharply.

What the reader should first understand is that because of such changes in engineering trends, the demands made on thermal design are greater than ever before. As mentioned above, compactness, high functionality, and also excellent design are demanded not only of equipment, but also of components, and measures to deal with heat have become a major concern. Thermal design is increasingly important insofar as it leads to improved reliability and safety of equipment as well as overall cost reductions.

In articles on thermal design on Tech Web, there are plans to introduce such basic topics as the importance of thermal design, thermal resistance, heat dissipation, examples of estimation of Tj, and thermal simulations.