Book Excerpt: Thermal Management With Insulated Metal Substrates, Part 4

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The following is an excerpt from Chapter 4 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.

Chapter 4: Application Examples

Main Application Areas
Insulated metal substrates find many applications in automotive and industrial LED, power conversion, general lighting, street safety, backlight unit, and e-vehicle sectors (Figure 4.1).


Figure 4.1: Primary applications for IMS.

Compact LED lamp units give car stylists extra freedom. Bright lighting at near-daylight color temperatures gives drivers a clear view. However, as much as 80% of the electrical power supplied is dissipated as heat, which presents engineers with severe thermal management challenges.

Matrix headlamps feature multiple closely-spaced emitters on a single substrate. A substrate of high thermal conductivity, featuring either an aluminum or copper baseplate, and dielectric thickness of about 0.002” (0.05 mm) is a typical choice to ensure long-term reliability. A non-reinforced dielectric minimizes stressors due to CTE mismatch between the copper foil and aluminum baseplate. A copper baseplate may be used if the matrix density is extremely high and the power is very high to address potential CTE mismatches. Spotlights with multiple boards, each containing two or three emitters, concentrate the thermal challenge on smaller substrates featuring an aluminum baseplate and 2–3 W/mK overall thermal conductivity including the dielectric layer, which is typically about 0.003–0.004” (0.075–0.010 mm).

Automotive Turn Signals
LEDs for turn signals are typically in the 3W power range. A three-emitter unit dissipates about 7 watts of thermal energy that must be extracted from the component. IMS is often the most efficient and cost-effective thermal connection to the metallic chassis. Extreme size and shape constraints can direct designers toward a substrate with 3 W/ mK thermal conductivity and 0.002” or 0.003” (0.05–0.075 mm) dielectric.

High-Power Motor Drive for Electric Power Steering
Electric power steering (EPS) and other motor-driven mechanisms, including high-power electric-traction inverters in EVs, can present even tougher thermal management challenges. Targets for module size and reliability can be met cost-effectively using a high-performing IMS with thermal conductivity of 3–4.2 W/mK and 0.004”–0.006” (0.10–0.15 mm) dielectric. Direct bonded copper (DBC) is an alternative. In extremely high-power applications, such as inverters, power transistors may be soldered to the IMS/DBC circuit layer as bare die, and a liquid-cooled heat sink attached to the baseplate. In some modules, such as combined onboard charger (OBC) and DC/DC-converter units for EVs, the baseplate is integrated with a cast metal chassis, and the specification determined in consultation with the foundry.

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