Conductive Material
Metallic sheets used to create the electrical pathways on a printed circuit board substrate. High purity copper foil is laminated onto dielectric base materials through heat and pressure to form the cladding for subsequent etching processes. This material is categorized by its weight per square foot, where one ounce equates to a thickness of approximately 35 microns.
Surface Treatment
Adhesion to the resin system depends on the roughness of the matte side of the metal. Manufacturers apply a secondary treatment to copper foil to create a dendritic structure that mechanically locks into the prepreg during lamination. Standard electrodeposited types offer high bond strength while rolled annealed varieties provide the flexibility needed for dynamic flex circuits.
Different profiles, from standard to very low profile, determine the skin effect losses in high frequency applications.
Etching Characteristic
Uniformity in the metal thickness ensures consistent impedance control across the entire panel. Chemical etching removes unprotected areas of the copper foil to leave behind the traces and pads defined by the artwork. If the process time or chemistry concentration deviates from the set point, over-etching occurs.
Thin foils allow for finer line widths and spaces because the lateral etch, known as undercut, is reduced. Handling 12 micron foil usually requires a carrier sheet.
