Pioneering Design-Class
Thermal Analysis for Electronics - III

<This article is the third in a series>

In the first two articles, we introduced an emerging class of engineering analysis software called Design-Class Analysis (DCA) and compared it to traditional analysis software. As you recall, traditional analysis software is centric to a particular field of analysis such as finite elements (FEA), computational fluid dynamics (CFD) or flow network modeling (FNM). DCA software is centric to the application of analysis techniques to design problems within a specific field of engineering. For Flomerics, physical design of electronics is the engineering field of choice. The differences between traditional analysis and DCA software are summarized below:

In the previous article we examined how DCA software improves the model creation process as compared to traditional analysis tools. In this article, we examine how DCA software enhances the design optimization process as compared to traditional software.

THE SHRINKING DESIGN CYCLE

Over the past ten years, design cycle time for development of electronic products has fallen drastically in response to consumer demand and fierce competition. Within the Flomerics customer base, design cycle time has dropped from 30 to 10 months for major telecommunications products. For smaller product upgrades, 3 to 6 month cycle times are common. At the same time, thermal densities and clock speeds have increased dramatically. Engineering teams are being forced to explore more design options in less time to keep up with these pressures.

Just 5 years ago a typical circuit board for a telecommunications product dissipated 100 watts. Thermal design back then was not particularly challenging, as the board itself is a sufficient heat sink for 100 watts in many cases. Today, 500 watts is common and now new, novel thermal designs are required. This is forcing engineers to spend significant time exploring design options in order to dissipate the heat generated. As a result, virtual prototyping in analysis software tools have become a mainstream design practice a key element for shrinking the design cycle.

How is DCA software different from traditional analysis software with respect to virtual prototyping? Aren't they both used for exploring design options before building real hardware? The simple answer is that DCA software is designed specifically to explore many design options in a short timeframe. Traditional analysis does not support the design process in this way. Let's take a closer look.

THE SHIFT AWAY FROM TRADITIONAL ANALYSIS SOFTWARE

A conceptual description of the product design process was introduced in the last article and is shown again in Figure 1. Stage one of the design process involves conceptualizing a baseline design in software. This is shown as "Model Build" in the figure and was covered in detail in the last article. Stage two is the design optimization phase and is the focus of this article.

Figure 1: A Typical Design Process

The need to practice design optimization for electronic products increases at a rate proportional to the increase of thermal density and clock speed. 10 years ago engineers could get away with rule-of-thumb product design without exploring design options. Today, thermal densities found on chips, boards and systems force engineers to explore many design options before a workable one is found. This has created an opportunity for companies to separate themselves from their competition. The fastest company to market with a quality product wins the game every time. DCA software meets this requirement. Rapid Design Optimization is a DCA concept that is becoming critical to the success of companies that must shrink design cycle times in order to stay competitive in the electronics industry.

RAPID DESIGN OPTIMIZATION: THE TECHNOLOGY OF THE FUTURE FOR PRODUCT DEVELOPMENT

The evidence of this is ubiquitous. For years, CAD companies have tried with little success to merge Model Building in traditional analysis with that of CAD. Just about every CAD company has an "integrated" analysis module but true, single model design remains a pipe dream. This is especially true in the electronics industry

As a engineer, what if you had unlimited resources available to build and test prototypes of your choosing? What if you could test dozens of circuit board layouts, heat sink designs or system configurations overnight? What if this was possible without having to watch over the process to ensure that nothing goes wrong?

Rapid Design Optimization automates the study of design options in software, freeing the engineer to spend time in other areas. FLOTHERM incorporates Rapid Design Optimization concepts for thermal design of electronics. For the first time, automated design studies are available to thermal engineers for tackling the challenging design issues created by today's high density electronic products.
As a simple illustration of Rapid Design Optimization, let's look into a basic question asked frequently during the design of heat sinks. How does heat sink performance vary with fin spacing?

We will answer this question by using FLOTHERM's Rapid Design Optimization functionality called Command Center. In FLOTHERM, we place the heat sink shown in Figure 2 in a wind tunnel. Using Command Center, we set up a Design of Experiments (DOE) study on the heat sink by defining a design space based on minimum and maximum number of fins. In this case, the design space is bounded on the lower end with five fins and on the upper end with 15.

Figure 2: DOE Study on Heat Sink

With Command Center, the design study was set up in less than a minute. After specifying seven DOE runs, FLOTHERM automatically setup seven different heat sink models with 5,6,7 9,10,12,13 and 15 fins each. A single mouse click on "Go" started FLOTHERM on solving the cases. After 15 minutes, all seven cases were complete and the following results were found:

Figure 3: Heat Sink Performance vs. # Fins

The results show that the optimum number of heat sink fins for this case is 12. Figures 4 and 5 explain the results. There is significant flow bypass for heat sinks with 12 or more fins illustrating the sensitivity of heat sink performance to flow bypass.

Figure 4: Low Flow Bypass	Figure 5: High Flow Bypass

With traditional analysis software, this simple study would have taken about 90 minutes. With FLOTHERM's DCA approach it took less than 20 minutes. Imagine the possibilities for complex design situations. FLOTHERM customers regularly study the effects of board spacing, component layout, fan position and other design variations using the DCA approach with Command Center. Hours of design time can be saved on typical sensitivity studies.

As FLOTHERM matures, true design optimization will become available further reducing design time and providing advanced functionality to help engineers pack more electronics into smaller spaces. The end goal for FLOTHERM is to provide a complete Rapid Design Optimization environment where true design optimization is automated, simple and effective.

Rapid Design Optimization is an exciting concept for progressive manufacturers of electronic products. For the first time design studies become a practical, routine part of product development for the electronics industry. In the near future, DCA concepts like Rapid Design Optimization and Design Flow Integration will be necessary to tackle the design challenges associated with high density, high performance electronics.