Differences between Roll Anneal Copper Foil and Electrolysis Deposition Copper Foil
Roll Anneal Copper Foil (RA copper):
Formation: Roll copper block many times, and then do the annealing treatment with high temperature. The shape of its crystal is lamellar structure.
Advantage: Soft, smooth surface, suitable for flexible PCB and small lines.
Shortage: high cost
Electrolysis Deposition Copper Foil (ED copper):
Formation: Melt copper into dilute sulfuric acid, it becomes bluestone solution.
Through a high electric field, copper attach on the metal drum. With the rolling of metal drum, thin copper foil finally formed.
Advantage: Low cost
Shortage: Unsuitable for small lines; bad bending resistance.
Here is the cross section observation of RA Copper and ED Copper:
As you can see, there’re adhesive in base for each four basic thickness of 2L (double sided) flex circuits, if you need more thin, then you can use adhesiveless material, and final thickness will be thinner even you use the same copper and Polyimide thickness. Please see next article (to be continued…)