Radio frequency (RF) and microwave PCB’s are a type of PCB designed to operate on signals in the megahertz to gigahertz frequency ranges (medium frequency to extremely high frequency). These frequency ranges are used for communication signals in everything from cellphones to military radars. The materials used to construct these PCB’s are advanced composites with very specific characteristics for dielectric constant (Er), loss tangent, and CTE (co-efficient of thermal expansion).
High frequency circuit materials with a low stable Er and loss tangent allow for high speed signals to travel through the PCB with less impedance than standard FR-4 PCB materials. These materials can be mixed in the same Stack-Up for optimal performance and economics.
The advantages of using materials with a low X, Y and Z CTE is a resulting PCB structure that will remain extremely stable in high temperature environments while operating at up to 40 GHz in analog applications. This allows for the effective placement of very fine pitch components including, in some cases, bare die-attach. Additionally, the low CTE materials will facilitate the alignment of multiple layers and the features they represent in a complex PCB Layout.
- CTEr = +40/+50 ppm per °C (low); Tg (glass transition temperature) is 280°C
- ER = 3.38/3.48 at 10.0 GHz
- ER is constant to 40.0 GHz
- ED (electro-deposited) copper only
- Layer-to-layer thickness control = +/- 0.001
- Fabrication costs are typical to slightly increased