There is a small but fast growing sector of the exotic market for PCBs where the base material needs to have predictable electrical performance characteristics at very high frequencies. Some of these electrical properties which are required include:
- Low dielectric constant (to provide maximum transmission speed)
- Low dissipation factor (to minimise losses and maximise signal transmission performance)
Most of the high frequency microwave substrates have an added bonus by offering superior thermal performance. One of the principal constituents of microwave materials is polytetrafluoroethylene (PTFE) otherwise known as Teflon. These PTFE based materials are expensive to produce and are priced accordingly. The lowest priced materials are about 5 times more expensive than standard FR4 materials. They are also hard to process due to the "slippery" surface characteristics of PTFE to which the addition of copper in the holes and soldermask on the surface is extremely difficult. As such, PTFE based materials are only used when absolutely necessary or where the amount of material is kept to a minimum and the cost effect is less critical.
The application of these microwave materials tends to be associated with operating frequencies at 1GHz and above. Although traditional materials like FR4 can operate in this frequency range, their electrical performance is not so good. There are several well defined areas in which microwave materials are critical to the performance of an electronic system. The number of applications is growing all the time as new opportunities open up in the market place. Some of these applications include:
- Satellite Broadcasting (Low Noise Amplifier on Satellite antennas)
- Mobile Phones (Filter unit)
- Box stations (power amplifiers)
- Vehicle Tolling (microwave scanning transmitter and receiver units)
- Auto Collision and Accident Prevention (microwave based "radar" type system)
- Microwave communication (transmission and reception applications)
- Military and avionics
- Global Positioning Systems
- Telecommunications
- Instrumentation
The available PTFE based materials can be broken down into 3 well defined areas:
- Woven materials which are based on a woven glass cloth fabric that has been impregnated in a PTFE suspension and then built up into copper clad panels. (lower priced)
- Non-woven materials which contain chopped glass fibre mixed in a PTFE slurry and then pressed, heated and laminated (better isotropic properties and more stable and predictable electrical properties).
- Ceramic loaded materials which incorporate chopped glass fillers to which ceramic materials have been added to raise the dielectric constant.
PTFE laminates combine a low dielectric constant with a very low dissipation factor. They come in a very wide range of grades, properties and specifications. Most of them have dielectric constants in the range 2.2 to 2.9, although some of ceramic loaded materials have values up to 12. Laminate manufacturers offer a range of cladded foils on different substrate thicknesses.
For further information on the available range of microwave materials contact our Customer Support staff.
