What is Prepreg in a PCB?

What is Prepreg? What is its purpose?

PCB Fabrication 
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Editorial Team - PCB Directory

Jan 19, 2022

Prepreg is an insulating layer within the PCB that helps bind multiple layers of a PCB. It can bind two cores or a core and a copper layer in a mult-layer printed circuit board. The Prepreg is an insulation layer that is made by combining glass fiber and a resin bonding agent. The name 'prepreg' comes from pre-impregnated. In this case, Glass fiber is impregnated with a resin bonding agent to create prepreg materials used in PCBs.

The thickness of a Prepreg material depends on the amount of resin content bound with the glass fiber. Based on the amount of resin content, prepregs can be divided in to three types - Standard Resin (SR), Medium Resin (MR) and High Resin (HR). High resin results in thicker prepreg materials that are more expensive.

The thickness and resin content in a prepreg regulates the impedance, dielectric constant, Coefficient of Thermal Expansion (CTE), and drilling / etching quality. 

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