PCB Designer should choose the type of laminate suitable for the purpose of the finished device.
The most important laminate parameters:
- thickness of base laminate – the thickness of the laminate on which no production processes were carried out,
- thickness of finished PCB – include : thickness of :copper foil, dielectric (FR4/ prepreg etc.), metallization, soldermask, surface finish, and tolerances of these thicknesses,
- glass transition temperature Tg – is the temeprature in which the laminate will begin to change from a solid to a liquid state – it can cause deformation or delamination. It is recommended to choose a laminate, that have Tg above 25°C of maximum operating temperature of designing divice.The number of soldering cycles and the choice of its method is also depends on the Tg parameter,
- thermal conductivity TC means the efficiency of heat transfer to enviroment and reduction of heat retention within the material,
- Comparative Tracking Index CTI (V) – breakdown strength between the circuit paths.There are 6 PLC (Performance Level Categories) classes - a higher class means, for example: PLC0 means a higher level of user safety,
- Coefficient of Thermal Expansion CTE – is the coefficient of thermal expansion of laminates that is projected along the XY plane and the Z axis. When the temperature rises above Tg, the CTE rises simultaneous,
- Dielectric constant permittivity Dk – Dielectric constant defines the relative permittivity of materials to vacuum,
- Df paramater – determines signal losses converted into heat due to material absorption.
| Type of laminate | Properties |
|---|---|
| FR4, FR4 with high Tg and FR4 halogen-free | The most popular laminate, used to PCB production - made of fiberglass and epoxy resin. It has a high dielectric constant, strongly dependent on frequency. |
| PTFE | PTFE is polytetrafluoroethylene, which has excellent dielectric properties on microwave and radio frequencies. It has low Dk and Df parameters. |
| MCPCB Metal Core PCB) | High thermal conductivity TC, high dimensional stability and hardness. Used in applications where efficient heat dissipation is important. |
| Poliymide (Pi) | Polyimide is a very durable laminate that is very resistant to chemical and environmental influences, with low CTE. Used in the production of Flex and Rigid-Flex circuits. |