PCB007 Magazine

PCB-Apr2014

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66 The PCB Magazine • April 2014 polymer then facilitates copper electro-plating on the non-conductive dielectric hole wall. An example of such a conductive polymer forma- tion is the oxidation of pyrrole to poly-pyrrole, using permanganate as the oxidation agent. The permanganate is reduced to manganese di- oxide, which is insoluble and needs to be fur- ther reduced to the soluble manganese Mn 2+ ion. Another example is the polymerization of "EDOT" (3,4-ethylenedioxy-thiophene) to po- ly-EDOT (Figure 1). The formation of resin coated foil (RCF) typically involves the use of a solvent or solvent mixture to form a resin solution for coat- ing onto a copper foil. Atotech has pioneered an alternative approach that does not require solvent for the formation of RCF. It is a solvent-free pow- der manufacturing technology called ADEPT (advanced di- electric epoxy powder technol- ogy). On-site Recovery and Recycling An example of such green processing is Atotech's Cu- praEtch DE, an iron sulfate- based etchant with minimal undercut for differential etch- ing in the so called semi-addi- tive plating process (SAP). The process runs in parallel with a regeneration unit in which the etched copper is plated out for recovery and the ferric etchant is regenerated. Elimination of Process Steps Laser direct imaging (LDI) is a good example for step elimination. The digital CAD data guide a laser directly as it scans the photoresist surface to form a resist pattern. LDI eliminates the need for a phototool and thus eliminates all processing steps and chemicals needed to generate the phototool. In addition, LDI cuts manufacturing lead time and allows scaling of the image, an image compensation to optimize for best fit to registration reference points. It should be mentioned that all digital imaging techniques offer the above mentioned advantages, whether they involve a laser or not. Substitution of Less Toxic Substances for Toxic Chemicals Modified Electroless Copper Bath Chemistries A traditional electroless copper bath uses formaldehyde, a suspect carcinogen, as a re- ducing agent. Some electroless copper baths have eliminated formalde- hyde and have replaced it with hypophosphite, for example. Traditional electroless cop- per baths have also used sta- bilizers such as cyanide and EDTA (ethylene diamine tet- raacetate). Cyanide is highly toxic and EDTA is a powerful complexing agent that inter- feres with the precipitation of heavy metals in waste treat- ment processes. Some electro- less processes have eliminated these chemicals and use tar- trate instead as stabilizer. Other examples of substi- tutions for problematic chemi- cals include replacing non- biodegradable substances with biodegradable chemcials, (e.g., in cleaners). Gold baths have been modified to eliminate cyanide. The elimination of lead from solder has been widely discussed, however the actu- al health and environmental benefits are debatable. Tin/lead solders have been largely replaced by the so-called SAC alloys (tin/silver/copper). Lead-free electroless nickel baths are now also available. The push to make base materials halogen- free is gaining momentum. Halogen-free is a bit of a misnomer because it really focuses on the elimination of tetrabromo bisphenol-A as a flame retardant for epoxy resins. While PTFE- GREEN TECHNOLOGIES IN PCB FABRICATION continues The elimination of lead from solder has been widely discussed, however the actual health and environmental benefits are debatable. Tin/lead solders have been largely replaced by the so-called SaC alloys (tin/silver/copper). Lead-free electroless nickel baths are now also available. " "

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