Thermoplastic circuit board

 

The choice of a material system for a given PCB (Printed Cicuit Board) application is nowadays strongly driven by costs. However, in today’s world of high-speed devices, advanced material packages, and need of reliability, the complete performance must be considered in the material selection process. Nearly all laminates suitable for PCBs, which partially fulfil the required properties, are based on fibre reinforced thermosetting polymers. An important example of this class of substrates is the low cost epoxy-based FR4 laminate.

At the department of Polymer Engineering, we have developed a new class of high temperature thermoplastics substrates for circuit boards, such as PEI, PES and PPS, which show a number of advantages compared to FR4 laminates:

  • Inherent flame resistance
  • Lower dielectric properties, making them suitable for high frequency applications
  • Higher temperature resistance, suitable for high temperature applications
  • Continuous manufacturing by extrusion, resulting in a highly automated process
  • Thermoforming after the assembly of the circuit board, providing a new degree of liberty for PCB design.

We developed two different classes of thermoplastic circuit boards: 1) based on foamed polymers; 2) based on highly filled polymers.

Foamed circuit board (HTT board)
Manufacturing process: foam extrusion

By employing physical or chemical blowing agents, high temperature thermoplastics can be foamed by extrusion, and therefore resulting in a much lower density (below 800 kg/m3) than standard FR4 substrates (1900 kg/m3). This is clearly a very attractive feature for the electrical mobility sector. At our department, we are further tailoring these thermoplastic substrates for specific applications, by controlling the foam morphology. Furthermore, we currently work also on the improvement of the process itself, with for example the implementation of a continuous copper lamination process.

Highly filled thermoplastic circuit board (LuVo Board / Heger Board)
Manufacturing process: extrusion

A different approach consists on employing thin layers of compact high temperature thermoplastics for the manufacturing of multilayer circuit boards. In such parts, a low coefficient of thermal expansion of the substrate is a very important parameter, as during manufacturing, the circuit board is heated up to 270 °C, and a large thermal expansion may lead to the delamination of the part. Our department was able to reduce the coefficient of thermal expansion of high temperature thermoplastics from approximately 50 ppm/K down to 17 ppm/K, by employing ceramic fillers (up to 60 wt%). Such highly filled thermoplastics are then suitable for the production of thin substrates (from 0.1 mm up to 1 mm) by extrusion. Regarding the final properties, these innovative substrates favourably compare to current high frequency substrates available in the market, and moreover, these thermoplastics have a much lower cost than other commercially available materials.

Contact: Dipl.-Ing. Stefan Mörl
Phone: +49 921 5574-72
Fax: +49 921 5574-73
Email: stefan.moerl@uni-bayreuth.de

Foamed thermoplastic circuit board
Multi-layer circuit board