In order to increase the circuit performance we need to increase the performance of base material. This can be achieved by

  • Circuit densification
  • Higher circuit operating frequencies

Performance Issues of PCB Base Material

 

Circuit densification:

To increase printed circuit performance is to place more circuitry per unit area of the printed circuit. Printed circuit densification has made many developments in copper foil technology

 

HTE Foil

High temperature elongation is class 3 copper foils that shows better elongation properties at high temperature. Has excellent ductility at high temperature. Prevents inner layer of copper foil from cracking

Performance Issues of PCB Base Material

 

Low profile and Reverse treated Copper Foils

performance1

The etching of low profile foil causes more control of geometry of the circuit tracks. On the other hand big tooth structures of standard profile and thin laminates can result inconsistent dielectric thickness resulting in difficulty of impedance control

Reverse treated Foils RTF has advantage. The etching of very fine circuit trace is possible. Second

Is improved photo resist adhesion.

 

Thin Layer Copper Foils

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The use of thin layer copper foil can result in etching file line circuits. For high density fine line circuits, 9.0 micron and 5.0 micron copper foils are used.

Performance Issues of PCB Base Material

 

Higher Circuit Operating Frequencies

As the signal frequency is increased to the extent of GHz the skin depth phenomena will occur wehre most of the signal is travelling though the outer part of conductor

This results in signal attenuation due to signal losses because of the rough surface of foil

As can be seen from graph the frequencies above 1 GHz show significant attenuation and higher roughness. The greater the roughness the greater the attenuation

 

Dimensional Stability:

Increasing the layer count in PCB and tightening the via-to-pad size will result in increasing the significance of alignment of the layers of circuit.  The laminate dimensional stability contributes in the capability to achieve layer to layer and via to inner layer feature registration. The thinner laminates are usually unstable than thicker laminates

 

 

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