Thermal Properties of Flex Circuit Boards

A flex circuit board, also known as a Printed Circuit Board (PCB), has a layer of metallic traces that are typically copper combined with an electrical dielectric material such as polyimide or polyester. The conductive copper is attached to the dielectric material using an adhesive or, more recently, via vapour deposition. The resulting laminate can be either a single-sided or double-sided PCB, depending on the design requirements.

Compared to rigid circuit boards, flex PCBs are thinner, more flexible and provide increased performance in harsh environments. Redesigning a product to use flex circuits instead of mechanical connectors can yield immediate weight reduction benefits and allow more space for additional features. In addition, reducing the number of point-to-point wires in a design improves reliability by reducing potential points of failure.

The material used to construct a flex circuit board determines its thermal properties. Conductors, which enable current to flow, are usually made of copper or aluminum and separated by insulators. Depending on the application, different insulations can be selected such as polyimide, polyester, solder mask or polyethylene naphthalene. The thickness of the insulators will impact how well the flex circuit board will withstand the amount of bending or flexing it will be exposed to during use.

What Are the Thermal Properties of Flex Circuit Boards?

In addition to the thermal properties of a flex circuit board, the choice of substrate material is important. Substrate material will have an impact on how well a flex circuit board can handle dynamic flexing and how much it will cost. For example, a substrate with high thermal conductivity is ideal for dynamic flexing applications as it can dissipate heat quickly and efficiently.

Flex circuits are used in a vast range of electronic devices from cell phones to aircraft navigation systems. In the automotive industry, flex circuits help engineers reduce the size of a vehicle by enabling them to include more advanced electronics such as climate control and GPS software. Additionally, flex circuits can be formed into unusual shapes that are better suited for fitting in vehicles than a traditional circuit board would be.

The medical industry is another significant user of flex circuits, and the selection of substrate material is especially important. The substrate needs to be chemically resistant so that it can withstand the various chemicals found in medical devices and implants. A flex circuit can also include a sleeve to protect the board from moisture and contamination.

The best way to select the right material for a flex circuit is to use Sierra Circuits’ free PCB material selection tool. This simple tool allows you to input a set of requirements and compare detailed properties of 50+ rigid and flex materials including DK, thermal resistance and moisture absorption. The more information you supply in the tool, the more accurate the results will be. Once you have selected the ideal material, our expert team can help you design a flex circuit that is both durable and cost-effective. To get started, please request a quote.