Book Excerpt: Thermal Management With Insulated Metal Substrates, Part 2

Reading time ( words)

The following is an excerpt from the second half of 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.

The thermal conductivity of a substance k is an intrinsic property that indicates its ability to conduct heat. Some relevant examples are illustrated in Table 1.1.

Heat can be dissipated from QFN components by mounting them on thermal pads connected to internal copper planes by thermal via holes. Problems of solder wicking into the holes and causing voided joints can be avoided by filling the holes with thermally conductive resin and plating them over with copper, or by completely filling the holes with electroplated copper. Solid copper “coins” can be bonded into recesses milled into the PCB to conduct heat away from individual power devices. All of these techniques can be effective, but they usually involve additional materials and processing, and a significant cost premium.

Ventec Book Table 1.1.JPG

Many power electronics and under the hood automotive devices are built on direct-bonded copper (DBC) substrates because of their strong thermal conductivity. They are based on a ceramic tile (commonly alumina) with a sheet of copper bonded to one or both sides by a high-temperature oxidation process. The top copper layer can be formed prior to firing or chemically etched using PCB technology to form an electrical circuit, while the bottom copper layer is usually kept plain so that it can be soldered to a heat spreader by soldering the bottom copper layer to it. Beryllia, silicon nitride, and aluminum nitride are more effective heat conductors than alumina, but cost considerably more. Further, thick-film technology can be used in some high-reliability applications. Thick-film technology offers a higher degree of design freedom than direct-bonded copper, but it may also be less cost-efficient.

LED manufacturers have adopted packaging technologies from the power electronics field with the result that they can now offer efficient thermal coupling from the semiconductor to the primary interconnecting substrate of the package. However, it remains that the only path for heat out of the LED is via the bottom of the LED package to the PCB, which must not present a thermal barrier. For high-power LEDs, the thermal conductivity of an FR-4 PCB is insufficient to enable effective heat transfer, and insulated metal substrate materials offer a better solution. These materials generally consist of a thermally-conductive dielectric layer heavily loaded with ceramic-type fillers that are sandwiched between copper foil and an aluminum or copper plate. The dielectric may be unreinforced or woven-glass reinforced.

To download this free eBook, published by I-Connect007, click here.

To view the entire I-Connect007 eBook library, click here.




Suggested Items

Eliminating ‘Garbage In, Garbage Out’ With Checks and Balances

03/26/2021 | Nick Barbin, Optimum Design Associates
The proverbial saying “garbage in, garbage out” holds true in the electronic product development world. PCB designers stand squarely in the middle of a busy information intersection flowing with inputs and outputs. Missing or bad information at the beginning of a design project will undoubtedly lead to board re-spins, increased costs, and most importantly, a delayed product release. The same can be said about the PCB designer who doesn’t provide a fully checked and comprehensive data package to the downstream manufacturers, i.e., “throwing it over the fence.”

Altium Introduces New Subscription Model

02/25/2021 | Andy Shaughnessy, Design007
Andy Shaughnessy chats with Lawrence Romine about Altium’s new subscription model for their Altium 365 platform. They discuss what this means for existing and future Altium customers, and some of the drivers leading to this development, including evolving use patterns among customers during the pandemic.

Seven Tips for Your Next Stackup Design

02/01/2021 | Eric Bogatin, University of Colorado, Boulder
Rarely do we have the luxury of designing a board just for connectivity. When interconnects are not transparent, we must engineer them to reduce the noise they can generate. This is where design for signal integrity, power integrity and EMC—collectively high-speed digital engineering—are so important. Eric Bogatin offers seven tips for stackup design.

Copyright © 2021 I-Connect007. All rights reserved.