Homebrew PCBs

I've followed a thread on the Tekscopes group for several days, hoping that 
someone would ask the question that's eluded me for years.  My question is 
in regard to the raw PCB manufacturing process; hopefully, someone can 
provide a clue.

My question is: what process is used to prepare the surface of the copper 
sheet prior to bonding to the bare fiberglass (e.g., FR4) board?  If you've 
ever lifted a trace from a PCB, you've probably noticed that the copper 
surface that was bonded to the fiberglass board had some kind of brownish 
coating on it.  Logic would lead one to think that this coating would help 
the copper to securely bond to the fiberglass.

I've noticed that on some boards, the copper-fiberglass bond is quite 
tenacious, requiring a good bit of effort to break it.  Applying heat and 
pressure is the easiest method, but physically pulling a copper trace form 
the board can be difficult if you're trying to salvage the trace.

I would like to know how the copper sheet is prepared prior to bonding to 
the board.  Anyone know?

Cheers,
Dave M 


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