PTFE and Controlled Dielectric Materials

PTFE laminates are used in circuit board design and production where the electrical loss from using standard FR4 epoxy resin is unacceptable. For these types of circuits the design itself behaves more as a component than on standard product. With the increasing requirement to make electronic goods faster, smaller and with more functions, PTFE and controlled dielectric circuits are becoming more of a necessity.

One important requirement in an RF or Microwave circuit board is to be able to transmit very fast signals. Traditional circuit board designs take the current from one component to another. Today circuits rely as much on the ability to maintain the signal speed.

When a signal is sent through a copper track on an FR4 epoxy resin circuit board, a certain amount of this current is lost through the material. In PTFE and some other hybrid material, this action is restricted and a calculation can be made to establish the size of track required to transmit and receive a desired signal.

Over the last few years the increasing requirement to run faster signals through circuit boards has caused some problems with passive inter-modulation (PIM). This effect is when a signal can interfere with signals running through adjacent tracks. The material suppliers have all tried to address these issues by supplying materials which are smoother at the copper/laminate interface, but just as important, we have developed better ways to clean and prepare the circuitry to reduce the PIM risk.

The PTFE laminates are generally graded by their dielectric constants (DK) and loss tangents. A designer can select materials with these 2 factors and coupled with the material thickness, make a judgement on what is required to perform a particular operation.

Most people encounter Teflon as a non-stick surface. We, as manufacturers using PTFE based products, have to employ specific procedures in our processing. The reliability of a plated through hole is dependant upon the initial conditioning and adherence of the conductive layer, prior to copper plating. Our production cycle etches the PTFE providing a micro porous surface to which a conductive graphite layer is applied. Copper can then be plated over this layer giving plated holes suitable for all types of assembly and long term reliability. Without these processes copper can be plated, but will not withstand heat cycles or survive in harsh environments.