The exposed core is processed through a chemical solution or developer that removes the resist from areas that were not polymerized by the light.
Inner Layer Etch
Then the copper is chemically removed from the core in all areas not covered by the dry-film resist. This creates the copper pattern that matches the film pattern.The core laminate
surface is exposed in areas where copper was etched away.
After etch, the developed dry-film resist is chemically removed from the panel leaving the copper on the panel. Traces, pads, ground plane and other design features are now
Automated Optical Inspection or AOI
Inner layers are then inspected against design rules using data from the gerber files. If allowed and practical, some repairs can be made at this point. Information on defects
is shared with the appropriate departments to correct any process problems.
After inspection the panels are chemically treated to improve adhesion of the copper surface. Advanced Circuits uses organic chemistry that leaves the copper
a dark brown. Other types of chemistry or mechanical methods can be used and colors vary widely.
The basic materials needed to build a multi-layer board are copper foil, prepreg and inner-layer cores.
The copper foil used in circuit boards is typically in sheets of ? oz. and 1 oz. per square foot in weight or 0.0007 and 0.00134 inches nominal thickness. In other words – one ounce of copper will cover one square foot when it is rolled out to a thickness of 0.00134”or 1.34 mils