Prepreg and core dielectric styles in PCB stackup

[engr_joni_ee]

I read that "common core dielectric thicknesses are 3mils, 4mils, 5mils, 6mils, 8mils, etc. Common prepreg glass styles are 106, 1080, etc. See the thickness and the dielectric constant of the generic prepreg glass styles in the table"

Does this means that the glass styles 106, 1080, etc are only applicable to prepreg and not to core, right ? This means we do not need to specify the glass styles in the stackup for core materials in stackup in degign tools ? as they are only for prepreg.

 

[FvM]

Cloth style apply also to laminates (core) but isn't always specified. Panasonic R-156 datasheet e.g. does.

 

[D.A.(Tony)Stewart]

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Many material properties; mechanical, electrical, thermal
Choose between required speeds and low loss. (which affects cost)
Rigid, Flex,

Cores have more fibreglass for strength.
Prepregs have more resin for filling around tracks. If no tracks then more fibre-prepregs can be used.

 

[engr_joni_ee]

Another related question to core and prepreg thickness. Is that ture that we avoid using prepreg more then 10 mils ? but we have have cured core available in different thickness that can be up to 40 mil. Any reason for not having prepreg more then 10 mil ?

 

[FvM]

There's no specific reason, although 10 mil is quite a lot. Criteria for chosing prepreg and core are overall PCB thickness for the intended number of layers, impedance considerations, in some cases also voltage strength, economic design. 10 mil or more prepreg means combining at least two sheets for the layer.

--- Updated Nov 24, 2023 ---

Generally you'll use PCB house standard stackup as long as it complies with your requirements.