A Thermal Conductivity Measurement Method, Adapted to Composite Materials Used in the PCB Industry

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Abstract

Most of today’s printed circuit board base materials are anisotropic and it is not possible to use a simple method to measure thermal conductivity along the different axes, especially when a good accuracy is expected. Few base material suppliers’ datasheets show X, Y and Z thermal conductivities. In most cases, a single value is given, moreover determined with a generic methodology, and not necessarily adapted to the reality of glass-reinforced composites with a strong anisotropy.

After reminding the fundamentals in thermal science, this paper gives a short overview of the state-of the art in terms of thermal conductivity measurement on PCB base materials, and some typical values. It finally proposes an innovative method called transient fin method, and associated test sample, to perform reliable and consistent in-plane thermal conductivity measurement on anisotropic PCB base materials.

Introduction

Observed on a long enough time scale, electronic systems behave like living species; they obey the laws of evolution. To be successful, they have to adapt to their environment, which means to market requirements, and thus to consumer expectations. Any system with a new, more powerful functionality naturally surpasses the previous generation. As consumers, we normally prefer smaller, lighter, faster, more reliable and cheaper electronic systems. This has led the electronic industry since its beginning.

The PCB progressively becomes a little bit more than just the backbone of electronic systems. At the beginning, the printed circuit board was providing essentially an electrical function, by interconnecting electrically components together, and a mechanical function, by supporting mechanically the components and holding them into a defined volume. Progressively, evolution towards microwave applications brought electromagnetic functionalities to the PCB. In addition, the constant increase of power density made the PCB more and more capable of providing solutions for efficient thermal management strategy.

To read this entire article, which appeared in the July 2016 issue of The PCB Magazine, click here.

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