Jim Wilson, Engineering Fellow
I have a small book in my office labeled “Suggestions for Designers of Navy Electronic Equipment, 1970 Edition” that was given to me several years ago by the editor at microwaves101.com (which happens to be a useful website if you are interested in microwave topics). The introduction states that any or all of this information is reproducible as long as credit lines are given so a few pages related to thermal management (including the nice illustrations) are reproduced in this column. An appropriate fact would be that thermal issues with electronics have been around as long as we have had electronics, but despite the long history of thermal management hardware and packaging solutions, it would be a fairy tale to think that cooling of electronics is easy. The suggestions in the book cover a range of topics that were of interest to end users of that time period such as design and reliability.
The book has 99 suggestions in the thermal section and perhaps not surprisingly, some of them still apply. This information was compiled before modeling and simulation was common or even practical with the computational resources of that time period. Expectations in 1970 relied on following generally accepted design practices and validation testing. Reasonable expectations of today are usually much more comprehensive and include simulations and confirmation tests. Densely packaged electronics with high heat loads that are common today would be difficult, if not impossible, to design without thermal simulation tools (and a thermal engineer to generate and interpret results).
The thermal section starts with rough guidelines on selecting natural, forced air, liquid or two-phase cooling based on heat flux. Advances in packaging and heat sink designs have made air and liquid cooling feasible at higher heat flux levels for both free and forced convection. General guidelines to consider when designing for natural, forced air, liquid, or vaporization cooling follow. The last suggestions are related to different types of electronics and while not many of us deal with tube cooling today, it is interesting to look at the integrated and other semiconductor devices section. Suggestion number 84 states that the thermal design of ICs are critical. This statement has proven to be true and is one of the main focus topics of Electronics Cooling. Suggestion 95 comments on validating parameters listed in manufacturer’s data sheets as they were found to be unreliable. Today, 45 years later, this is still good advice.
In the field of electronics thermal management, we have significantly more design capability today than existed when this book was compiled. However, a good lesson for all of us is to remember that this book was written from the end user’s viewpoint. We should make sure that considering the customer’s perspective in our thermal management designs has a high priority.