Another Important Issue after Miniaturization, Efficiency Enhancement, EMC : Thermal Design : Overall Thermal Design Must be Based on Common Understanding of the Engineering

―In addition to changes in engineering trends such as miniaturization, sophisticated functionality, and design properties, are there any other important factors?

Despite this tendency for higher heat generation densities due to these changed engineering trends, there has been, especially in automotive equipment and industrial equipment, a demand for extended service lifetimes. For semiconductor components as well as other components, there is an interrelation between operation lifetime and temperature; put simply, the higher the temperature during operation, the shorter the lifetime. Semiconductor components, by their nature, are designed for improved efficiency and reduced power consumption, so as to reduce the heat generated by the component. But in fact, more than ever today, measures for heat dissipation have become indispensable.

And, as always, demands for cost reductions are extremely stringent. In addition to simply reducing the costs of materials, in order to reduce reworking insofar as possible before mass production, highly precise thermal design in the initial stage of design is required. For this purpose, information, engineering, knowledge, and tools are necessary, and these must be used effectively. It goes without saying that there is an enormous difference in the money, time, and effort expended when problems are discovered in prototype evaluations before mass production so that prototyping must be repeated two or three times, and when diligent thermal design is performed in the initial stage and prototype evaluations need be performed only once.

Moreover, in addition to such design costs, there are not a few cases where quality complaints and recalls develop into public problems, which are bound to incur huge costs and damage the company’s reputation. In actuality, in the fields of electronic products and automobiles, heat-related defects and recalls occur continuously and without end.

For these reasons, there is a need for thermal design that achieves heretofore unreached levels of safety and reliability, despite the increasingly harsh conditions due to increasing heat.

―I see. To summarize, thermal design is essentially important, but with mounting demands for miniaturization, sophisticated functions, and design properties in the components and equipment of recent years, conventional thermal design approaches are insufficient in an increasing number of cases. In order to cope with such demands, more advanced engineering, knowledge, information and tools are needed, together with their effective use, bringing thermal design to the next level, so that we can confront these major issues. Is that about right?

Yes, that’s right. Moreover, in order to deal with the need to reduce costs and avoid complaints in the marketplace, thermal design that is more precise than ever before will be needed.

―Are there any proposals or the like to resolve these problems?

I have been visiting customers and conducting on-site seminars on thermal design, and providing thermal design support for individual cases. When I listen to designers describe actual issues at their companies, I come to feel that we need to consider other things in addition to the engineering.

For the design of a single product, speaking broadly, electronic circuit design, mechanical design relating to the housing and structure, printed circuit board design, and software design are needed. Depending on the company, engineers may be assigned to each of these tasks, or they may be allocated to separate divisions, or a single engineer may be tasked with multiple design tasks. Various methods are used, but where recent thermal design is concerned, I think it is important that all of these engineers share a common understanding that, in contrast with heat issues in the past, approaches to thermal design have also changed. By grappling with overall thermal design based on this shared technical understanding, I think that we will be able to overcome the problems I described earlier and satisfy the demands imposed.

―Earlier, you said that highly precise thermal design is needed, and that engineering, knowledge, information, and tools are necessary for this. What exactly is needed?

With respect to knowledge, an understanding of both heat transfer engineering and fluid dynamics will prove to be highly useful, I think. At the very least, with some understanding of heat transfer engineering, one should be able to try various approaches. In addition, an understanding of thermal resistance network methods will also be needed.

Also, use of heat conduction simulators and thermal fluid simulators is highly effective. I think that simulators will essentially be necessary for thermal design going forward. Recently a number of excellent easy-to-use simulators have appeared. As the thermal simulation models needed for simulations, models supplied by component manufacturers can be used.

As for sources of information, there is the website of the Semiconductor Packaging Technical Committee _*1 of JEITA (The Japan Electronics and Information Technology Industries Association). When models necessary for thermal simulations cannot be obtained from manufacturers, this semiconductor package thermal parameter estimation tool _*1 can sometimes be used instead.
_{*1:Japanese only.}

―At ROHM, what kinds of efforts and support activities are in progress?

ROHM is participating in the JEITA Semiconductor Packaging Technical Committee I mentioned earlier, and, via this committee, is studying the revision and addition of standards relating to thermal resistances. We are defining various thermal resistances and establishing guidelines relating to characteristic fluctuations due to different parameters, usage methods, problems, and the like.

Providing models for thermal simulations is also possible. For some time we have been providing thermal resistances θ_JA and θ_JC, and can also provide values for θ_JA, Ψ_JT, θ_JCtop, and θ_JCbot conforming to the JEDEC standard JESD51. And, for separate customers, we can provide support related to thermal simulations and to thermal resistance measurements. For this, we ask our customers to please inquire individually.

―Finally, could you please give a summary.

Changes in engineering trends in recent years are complicating the situation with thermal design. A clear understanding of this situation, and a deeper shared understanding among designers and divisions to deal with problems jointly, will be key to cutting costs and enhancing product reliability and safety.

On Tech Web as well, we are publishing articles relating to thermal design in the Basic Knowledge corner. We would encourage engineers to consult these articles as well.

―Thank you very much.