RealTime with... American Standard Circuits: Thermal Management

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In the third of a series of three RealTime with... American Standard Circuits intervews, I-Connect007 managing editor Nolan Johnson received knowledgeable and informative answers from Anaya Vardya, John Bushie, and Dave Lackey of American Standard Circuits to his questions on the topic of thermal management.

Anaya Vardya began by clarifying the terminology, describing thermal conductivity as a material property defining how quickly heat was transmitted through a piece of that material, whereas thermal management was about analysing the entire system, trying to understand how much heat was being generated, and using appropriate techniques to dissipate that heat as efficiently as possible. On printed circuit boards, straightforward solutions like thermal vias and heavy copper weights could be used for dispersing heat from packages. He invited Dave Lackey and John Bushie to discuss some of the more esoteric techniques.

Johnson asked Lackey to explain the difference between insulated metal substrates and metal-clad PCBs. There was basically none; both design structures involved bonding the PCB to some sort of metal substrate. A simple example was a single-sided circuit board bonded to an aluminium plate with a thermally conductive adhesive material, such as was commonly used to dissipate heat from LEDs. For additional capability, a double-sided PCB with plated through-holes could be used, fabricated on a substrate of FR-4 or thermally conductive laminate, and bonded to an aluminium plate with thermally conductive prepreg.

Another option was to bond circuits on both sides of a metal core, usually aluminium or copper. The two circuits could operate independently or be interconnected by plated-through-holes drilled through insulating plugs in the metal core. Lackey discussed several alternative metal-backed and metal-core alternatives.

Johnson was interested to learn whether multiple functions could be achieved. Bushie picked up this query. In general, with higher levels of integration and more power per unit area, more attention was paid to thermal management using a variety of techniques and materials, combining multiple functions as well as dealing with the heat. Bushie commented on the increasing convergence of RF and digital circuitry in the same design, together with the growing need for thermal management. People were starting to integrate metal cores into these designs, to decrease the overall package size. His example was a multi-function PCB with the control circuitry on one side of the structure and RF circuitry on the other side. Low-loss RF materials, high-speed digital materials, thermally conductive materials, and metal cores were integrated to increase the functional density of the structure. With flexible circuitry being progressively incorporated to minimise connector real-estate and increase reliability by eliminating cables and connectors, all these materials were coming together into a multifunctional circuit board, and what may have been two, three, or four discrete circuit boards could be combined into one smaller package with a higher level of functionality and a variety of circuit structures.

Johnson remarked that with all these dynamics in play—metals, materials, thermal management—designers were faced with difficult choices, maybe for the first time, often with limited experience. He asked Bushie what advice he would offer.

“This starts to sound like an old song...get your fabricator involved!” Bushie responded. “There’s a wealth of knowledge and applications engineering experience at your fabricator; we’re here to help. At the end of the day, we want to help you design something that we can make—rapidly, reliably, and functioning as you wanted it. Feel free to utilise us.”

In 12 minutes, this RealTime with... ASC video combined a primer in thermal management, an indication of how complex a topic it could turn out to be, and a comforting assurance that there is an abundance of support and assistance available to guide the designer through the maze of material selection and structural possibilities, provided that the fabricator is consulted at the beginning of the process rather than expected to sort out the deficiencies of an inferior design when it is presented for manufacture. I enjoyed the experience!

Pete Starkey is an I-Connect007 technical editor.

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