As electronic circuits' operating speed has increased, so needs for PCBs to have controlled characteristic impedances, and the majority of PCB manufacturers are producing impedance control PCB for many applications.
Impedance, measured in Ohms (symbol Ω), is somewhat different than resistance. Impedance is an AC characteristic, while resistance is a DC characteristic. Impedance becomes essential as the signal frequency increases, typically becoming critical for PCB traces at signal components of two or three hundred MHz and above.
At high frequencies, PCB traces do not behave like simple connections. When PCB board traces carry signals containing high frequencies, The PCB manufacturer must pay attention to to design traces that match the impedance of the driver and receiver devices. The longer the trace, or the greater the frequencies involved, the greater the need to control the trace impedance. Controlled impedance helps us ensure that signals are not degraded as they route around a PCB. The PCB manufacturer controls the impedance by varying the dimensions and spacing of the particular trace or laminate.
There are a few factors that affect the printed circuit board controlled impedance include: dielectric thickness, trace width, copper thickness, dielectric constant Er of the material selected for the stack, and thickness of the solder mask.
Trace width: The larger the trace width is, the lower the impedance will be. The thinner the trace width, the more impedance is offered. Increasing the board thickness increases the impedance while reducing it will decrease the impedance.
dielectric thickness: dielectric thickness also affects impedance. The dielectric strength of a material is a measure of the electrical strength of an insulator. It is defined as the maximum voltage required to produce a dielectric breakdown through the material and is expressed in terms of Volts per unit thickness.
Copper thickness: The copper thickness is also considered while calculating the trace impedance in high speed and RF digital circuits.
thickness of the solder mask: Solder mask can impact PCBs with RF circuitry on the outer layers, which can lessen high-frequency electrical performance.
|Monthy Capability||3650 m²/month|
|Finished board thickness||1.6m|
|Min Trace Width/Space||8/8mil|
|Min hole size||0.25mm|
|Min copper in hole thickness||1oz|
|Outer layer Finished copper thickness||3oz|
|Inner layer base copper thickness||3oz|
|Impedance Control Tolerance||±10%|