CopperCopper foil is the most common metal for base materials for PCBs. GTS has a long-standing experience in making flexible copper clad laminates. More
There are two main types of copper foil used in the FPC market:
a) Electrodeposited (ED)
b) Rolled-Annealed (RA)
a) ED Foil
ED foil has two distinguishing different surfaces. A matt or rough side which has significant peaks and valleys to promote adhesion. This is the matt side of the copper which was grown from the copper sulphate bath. Secondly, a shiny side which is the side that was against the rotating metal drum during the electrodeposition process. This is a reflection of the surface morphology of the drum.
The base copper foil is treated to further enhance the roughness of the matt side hence increasing the foil's ability to bond to dielectric materials as well as passivated for long-term storage.
Standard thickness for flex applications is 9, 18, 35, 70 and 105µm. Foils are also known by their weights - commonly by the term ounces per square foot or just ounces or 'oz' (9=1/4oz; 18=1/2oz; 35=1oz; 70=2oz; 105=3oz).
Copper foil is specified by its weight rather than thickness to ensure a certain conduction of electricity. The thickness is more indeterminate due to the roughness of the foil.
b) RA Foils
These foils are produced by rolling from copper ingots, followed by an annealing process to make them softer.
The direction of the grain structure is horizontal and the surface roughness is much less than that of ED foil. The softness plus the grain direction means that this type of foil is much better for flexing than the ED foils. This is the copper of choice for dynamic (moving) circuits.
A treatment layer will be put on the surface similar to ED foils, however the surface roughness will only be a few microns as the base foil is essentially smooth.
Most common thicknesses are 18µm, 35µm and 70µm.Less