Prepreg, short for pre-impregnated, is fiberglass cloth coated with resin cured only to an intermediate B-stage, so it is dry to handle but flows and fully cures when heated under pressure in the lamination press. Sheets are stacked between etched cores and outer copper foils to bond a multilayer board and form its dielectric layers. Glass styles such as 106, 1080, 2116 and 7628 differ in thickness and resin content, which sets the finished dielectric thickness and its dielectric constant.
Swap the two plies of 2116 prepreg for a single 1080 between layers 1 and 2, we need a thinner dielectric for the 50 ohm microstrip.
Also heard as
- pre-preg
- B-stage
- bonding sheet
Do not mix it up with
- Core: A core is fully cured laminate with copper on both sides; prepreg is the uncured bonding layer between cores.
Related terms
Core
Fully cured laminate with copper on both sides, etched into inner layers and bonded with prepreg into a multilayer.
Stackup
Ordered arrangement of copper layers, cores and prepregs that makes up a multilayer board, with each thickness.
Laminate
Sheet of reinforced resin, usually clad with copper foil, that rigid printed circuit boards are built from.
Dk
Dielectric constant: how much a board material slows signals and sets trace impedance, relative to vacuum.