Thermal management from design concept through final validation

October 31, 2013 // By John Isaac and Ian Clark, Mentor Graphics

An optimised design versus an indifferent one can significantly affect the competitiveness of the product and improve the bottom line of the developing company. In addition, reliability of the product can have significant effects. If the product has low reliability and fails in the field, not only does the company suffer huge warranty and recall expense but the failure may also compromise its reputation.

One prime driver affecting a product’s reliability is good heat management. However, managing the heat in a product is becoming increasingly more challenging because as ICs get faster and denser, the heat density increases (Figure 1).

Figure 1. Power dissipation of chips, and the increase in power density on those chips, have been increasing as shown in this plot of power density, watts per square centimeter (Source: “Circuit, Platform Design and Test Challenges in Technologies Beyond 90 nm,” Grundmanm, Galivanch, DATE 2003).

The increase in power density of ICs is compounded because PCBs are getting smaller and denser, and the product form factors are also getting smaller, which means more functionality, more heat, squeezed into smaller areas. Figure 2 shows data gathered from designs submitted to the Mentor Graphics Technology Leadership Awards program over the past 17 years. While the area of the average PCB submitted has gone down by a factor of 50%, the density of components has increased 350%. This represents a 700% increase in density on the average PCB. Coupled with increasing power dissipation per IC, we have a real heat management problem. Appropriate cooling strategies are needed to prevent overheating, and failure of critical components.

Figure 2. In recent years, the heat density on PCBs has increased significantly.

Managing heat in a system (Figure 3) is a multi-level challenge. Just because you have an IC package that is thermally optimised does not mean you have a good system. Likewise, good heat management at the PCB level does not guarantee high reliability. You must ensure that you have done good design and thermal analysis at three levels including the ICs and PCBs in the product enclosure. This can only be achieved using highly sophisticated computational fluid dynamics (CFD) software that considers convection, conduction, and radiation heat transfer of the entire system.

Figure 3. Good heat management is required for all electrical products.

Driving factors

The following are some of the driving factors for using efficient CFD thermal simulation software during the design process as well as considering heat management design from concept through design exploration and optimisation to final verification:

  • Getting the product to market on time. Missing the schedule by only a few weeks might miss the ideal market window and cost the company millions.

  • Enabling the designer to experiment with several design approaches. This results in a higher quality, better performing, and more competitive product.

  • Reducing the need for multiple physical prototypes. These are expensive and very time-consuming.

  • Delivering a product with high reliability saves warranty and recall costs as well as company reputation.

Figure 4 shows two very different thermal design approaches. The red triangle shows a traditional process where thermal design

The mechanical design of a system is no longer the gating factor in the on-time delivery of a product, but rather it’s the design of electronic components and software that increasingly causes delays. The electronics must not only be designed quickly but also meet high performance, quality, and reliability standards.
Mentor Graphics, Thermal design, CFD, Flotherm