# PCB Glossary: Dielectric

**URL:** <https://sierraconnect.protoexpress.com/t/pcb-glossary-dielectric/3046>\
**Category:** PCB Glossaries\
**Tags:** dielectric\
**Created:** [April 3, 2025, 1:59pm UTC](https://sierraconnect.protoexpress.com/t/pcb-glossary-dielectric/3046 "2025-04-03T13:59:28Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Mohamed\_Faheemuddin](https://avatars.discourse-cdn.com/v4/letter/m/4da419/32.png) [@Mohamed\_Faheemuddin](https://sierraconnect.protoexpress.com/u/Mohamed_Faheemuddin)\
**Post date:** [April 3, 2025, 1:59pm UTC](https://sierraconnect.protoexpress.com/t/pcb-glossary-dielectric/3046/1 "2025-04-03T13:59:28Z")

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A [dielectric or substrate](https://www.protoexpress.com/blog/pcb-substrates-knowing-dielectric-materials-properties/?utm_source=sierraconnect&utm_medium=display&utm_campaign=glossary%2Bdielectric%2Bthread%2Bapr%2B2025) is an insulating material used in PCBs to isolate conductive layers (signal, ground, and power planes). Dielectric materials influence signal propagation speed, energy storage, and thermal stability.

Common dielectric materials include FR-4, PTFE, polyimide, and ceramic-based materials. Each type offers different electrical and mechanical properties suited to specific applications, such as high-frequency, high-temperature, or flexible circuits.

 ![PCB stack-up with dielectric and copper layers](https://global.discourse-cdn.com/sierraconnect/original/1X/c3054b08e165498bf85baa319d1f7c28fa04b2fa.png)

When you’re choosing a dielectric material for your circuit board, consider the following properties:

**Dielectric constant (Dk)** measures the ability of a material to store electrical energy in an electric field. It directly affects the capacitance between conductors and influences the propagation speed of signals through the material. Dk ranges between 2 and 10.

**Dissipation factor** **(Df)** determines the extent of signal loss in a dielectric material. The higher the Df, the higher the signal attenuation. Df ranges between 0.02 and 0.001. A lower dissipation factor means less signal loss. For high-speed designs, pick a material with Df\<0.005.

**Glass transition temperature (Tg)** is the temperature at which the material transforms from a solid to a viscous state. Always choose a dielectric with Tg greater than the maximum operating temperature.