The Printed Circuit Board Designer’s Guide to… Thermal Management with Insulated Metal Substrates, Vol. 2′

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Excerpt Chapter 5: A Printed Circuit Board Designer’s Guide to… Thermal Management with Insulated Metallic Substrates, Vol. 2′

Chapter 5: Improving Thermal Performance with Multilayer IMS
In PCB Designer’s Guide to… Thermal Management with Insulated Metal Substrates (Vol. 1)the authors briefly discussed the problems associated with combining multiple layers of copper foils, dielectric materials and substrates and the design opportunities offered by the latest generation of thin cores and thermally conductive prepregs.

The latest thermally conductive materials, prepregs and cores allow designers to reconsider the approach to thermal management. They can offer a simple, out-of-the-box solution to address thermal issues on existing multilayer boards.

Out of necessity, the industry has already come up with many solutions over the years, such as thermal vias, thermal parts, and inserts. All of these existing solutions require either the use of thick copper sheets and/or the use of heavy copper coins, thus leading to inevitable cost and weight inflation. We can now analyze alternative designs made possible by the arrival of multi-layer IMS. The following application examples illustrate the concept and main advantages of multilayer IMS.

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Figure 5.1: Simple one-sided layer.

PCB design with insulated metal substrates is by no means limited to single-sided, single-layer circuits (Figure 5.1), although these are primarily the types of circuits used in electronics applications. LED lighting and power electronics.

There are several versatile ways to take advantage of the improved thermal properties of IMS in situations that require various other attributes such as physical formability or conformance, complex shape or small dimensions, or complex circuit layout that would be fulfilled with a multilayer PCB if it wasn’t for the thermal issues.

If a formable grade of laminate (such as, for example, 5052 aluminum with a thin, unreinforced dielectric) is specified, a single-sided circuit can be post-formed into three-dimensional shapes. It can help to design a printed circuit board that needs to fit in a small or unusually shaped package, or cram more electronic circuits into a limited space, or maybe make it easier to assemble a product if it doesn’t. There is only minimal access to install electronic circuit boards. The aluminum layer is machined to reduce its thickness in the bend area.

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Figure 5.2: Single-sided double layer.

Additionally, it is possible to build isolated metal substrates in multi-layer IMS structures (Figure 5.2) with thermally conductive laminates and prepregs using plated through holes for the Z-axis interconnect.

In situations where metal base is not an option, but component temperature needs to be reduced, alternative construction may be required; thermally conductive cores and prepreg can be combined to create the entire board or can be used in a hybrid construction combining traditional FR-4 and thermally conductive cores or prepregs.

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