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Base material of printed circuit boards: a few words about laminates

Łukasz Romik

The base material used to produce the PCB affects the reliability and efficiency of the final product.
The laminate may be selected based on two criteria: quality and functionality.
Currently, printed circuits are manufactured using laminates on the following substrates: glass-reinforced epoxy (FR4), aluminium MCPCB (Metal Core PCB), Teflon, or ceramic (microwave). Usually the material is selected as per predicted working conditions and the device type. Unfortunately, the decision-making process must also include the economic factor that imposes a compromise. Keep in mind that using high-quality materials is a key factor to provide reliability and long life of the device.
The parameters that define the quality and application/functionality of the device are listed below.
Basic parameters:
  • Non-conductor and copper foil thickness – mechanical resistance, fitting the case, current-carrying capacity, etc.;
  • CTI class – breakdown strength between traces in wet ambient conditions;
  • Fire resistance class (UL) – specifies the flammability of materials.
Temperature parameters:
  • glass transition temperature (boundary): Tg – yield point;
  • chemical decomposition temperature of laminates: Td – temperature causing 5% loss of laminate weight;
  • delamination time: T260/288 – time after which delamination occurs (for temperatures 260 and 288°C);
  • the coefficient of thermal expansion of laminates that is projected along the XY plane and the Z axis: CTEZ,XY;
  • max. operating temperature (MOT) – safe temperature for continuous operation.
Humidity absorption:
  • max. moisture content in laminate;
  • resistance to CAF;
  • Electric parameters
  • dielectric constant Dk;
  • lossiness Df;
  • dielectric breakdown strength.
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