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The following is an excerpt from Chapter 1 of The Printed Circuit Designer's Guide to... Thermal Management with Insulated Metal Substrates, written by Ventec International Group’s Didier Mauve and Ian Mayoh. In this free eBook, the authors provide PCB designers with the essential information required to understand the thermal, electrical, and mechanical characteristics of insulated metal substrate laminates.
This eBook will provide the PCB designer with the essential information required to understand the thermal, electrical, and mechanical characteristics of insulated metal substrate (IMS) laminates, to select and specify the most appropriate material for a particular thermal management application, and to achieve a reliable and cost-effective design.
Thermal Management of Electronics: The Needs and Benefits
The need to dissipate heat from electronic modules and assemblies is an increasingly important design consideration. This may be just one possible consequence of the inevitable “smaller, faster, cheaper” trend for microelectronics to operate at higher performance levels. For example, in the field of automotive engineering, an increasing number of functions like braking and power steering, which were previously achieved mechanically, are now being solved electronically.
Power electronics is another area where thermal management is a critical consideration in the design of DC power supplies, inverters, power conversion systems, and electric motor control applications. Thermal management becomes especially significant in the automotive industry as electric traction systems are progressively introduced.
Recent advances in high-brightness LED technology have led to its rapid adoption in municipal, domestic, industrial, and automotive lighting applications. Effective and consistent thermal management is essential to maintain the brightness and color spectrum of an LED light. Its life expectancy is closely related to operating temperature, and can be doubled by a 10°C reduction in operating temperature. McKinsey’s 2012 Global Lighting Market Model suggest that LED technology will capture over 70% of the global lighting market by 2020.
These forecasts have generated exponential growth and created huge market demands for efficient, reliable, cost-effective thermal management solutions, which in turn drive the development of thermally-conductive printed circuits as a preferred option. Keeping heat-generating components cooler increases component life, product life, and long-term reliability. The trend to increase the use of insulated metal substrates is driven by the need to reduce system costs, and reduce or eliminate the need for costly and bulky cooling fans and heat sinks. Meanwhile, a standard FR-4 laminate has a thermal conductivity coefficient of around 0.25 W/mK. Thermally conductive prepregs, laminates, and insulated metal substrates now offer thermal conductivity coefficients of up to 10 W/mK, and development will continue.
Thermal Awareness at the Design State
Dennis Price, quality director at Merlin Circuit Technology, began his presentation on heat dissipation methodologies at the 2016 Institute of Circuit Technology Northern Seminar by expressing concern that a designer survey had indicated that heat dissipation was considered a low design priority by many engineers, and that the majority of designers did not consider thermal management early enough in the design. More than one in four only considered thermal issues after the design had been completed, and more than half only tested thermal design on the first prototype, if at all. It was the view of many designers that thermal simulation techniques were too complex and time consuming! However, it is important that thermal awareness and thermal management be considered and addressed by designers.
Removing Heat: What are the Options?
There are three main ways to dissipate heat from a component: by conduction into the PCB, by convection into the local environment, or by radiation to any other surface. Conduction and convection are the only realistic methods of heat transfer, except maybe in space where radiation is probably the only option, and conduction through the substrate is likely the most efficient. Although common printed circuit laminates provide strong electrical insulation, they are generally good thermal insulators as well, so various features have been incorporated to promote heat dissipation. Features include bonded external heat sinks, through copper-invar-copper constructions that serve the additional purpose of CTE control, and heavy copper single or multiple internal heat planes.
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