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“Green” and “environmentally friendly” are ill-defined terms. In general, these terms refer to manufacturing that involves the replacement of toxic substances with less toxic materials, the elimination of materials or processing steps, and less consumption of chemicals (i.e., more efficient or higher yield processing, reduction of water use, reduction of energy use, less space requirement, smaller equipment foot print, and recycling and on-site recovery of materials).
This family of processes eliminates the electroless copper process. These processes typically have fewer process steps, use less rinse water, have less floor space requirement, and use less toxic chemicals. Direct metallization processes include:
These processes pretty much follow the classic electroless copper processing step sequence, except the sequence ends with the application of the palladium catalyst, followed by the activation, then skips the electroless bath and proceeds to copper electro-plating.
Carbon or Graphite-based
Using small carbon or graphite particles to render the dielectric hole-wall electro-platable, this process involves very few steps.
The process of using a non-conductive monomer to coat the board surface follows an oxidation step that forms a conductive polymer from the non-conductive monomer. The polymer then facilitates copper electro-plating on the non-conductive dielectric hole wall. An example of such a conductive polymer formation is the oxidation of pyrrole to poly-pyrrole, using permanganate as the oxidation agent. The permanganate is reduced to manganese dioxide, which is insoluble and needs to be further reduced to the soluble manganese Mn2+ ion. Another example is the polymerization of “EDOT” (3,4-ethylenedioxy-thiophene) to poly-EDOT.
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Editor's Note: This column originally appeared in the April 2014 issue of The PCB Magazine.