About twenty years ago, there were two processes for making copper circuitry
- Subtractive where etchant was used to form the circuits by taking away
(subtracting) the copper foil, - and Additive where a chemically resistant
plating resist was imaged on bare laminate and the copper electrolessly
plated up (added) to form the traces.

Today, the additive plating resists (solvent developed) are nearly gone, and
the full "additive" process used relatively little except for Japan.

About tweny years ago, someone thought of using conventional electroless
copper on a bare laminate substrate to form a thin conductive skin
everywhere.  Then, aqueous plating resist could be used and the much faster
electroplating process could build up the circuitry.   Once plated up, the
imaging resist is removed, and the thin electroless copper etched quickly to
isolate the circuits.

Today, semiadditve processing is used for "deposited dielectrics" - either
photosensitive or laser ablated - in forming microvias.

Denny Fritz
MacDermid, Inc

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