Printed circuit board finish

III. LEAD-FREE PRINTED CIRCUIT BOARD FINISHES... 

B. Lead-Free Printed Circuit Board Finishes... 

Base Metal Finishes. The low cost of base metal finishes obviates selective coating. Electro deposition is used for 0.5—5 p.m thick coatings of tin and tin—lead alloy, usually about 50 wt % Sn, 50 wt % Pb, on electronic connector contacts, on contacts at the edges of printed circuit boards, and on terminals. Sheet copper alloys that have been coated with tin—lead alloy are widely used for contacts that are stamped and then formed into the desired shapes, such as pins having a closed end and sockets. Aluminum connectors that have utility—industrial appHcations are more thickly coated, and hot-dipping in molten tin is common. 

U.S. PSES for All Metal Finishing Plants Except Job Shops and Independent Printed Circuit Board Manufacturers... 

MSA and other lower alkanesulfonic acids are useful for plating of lead, nickel, cadmium, silver, and zinc (409). MSA also finds use in plating of tin, copper, lead, and other metals. It is also used in printed circuit board manufacture. In metal finishing the metal coating can be stripped chemically or electrolytically with MSA. MSA also finds use in polymers and as a polymer solvent and as a catalyst for polymerization of monomers such as acrylonitrile. MSA also finds use in ion-exchange resin regeneration because of the high solubility of many metal salts in aqueous solutions. 

The U.S. EPA regards meialhzcrs such as platers, surface finishers, and printed circuit board producers as among the mosi impurtani source polluters for metals Much production of electroplated items lias, however, shifted from the United States to less environmentally stringent countries. 

Frequently, printed circuit boards are finished by deposition of an alloy of lead and tin, which facilitates soldering. 

The single largest use for the phenol-formaldehyde resins is in adhesive applications for the production of plywood, chipboard, and particle board. The resin can comprise as much as one-third of the weight of the board, particularly of particle boards, which contributes to a total demand for phenolics in the U.S.A. of over half a million metric tonnes per year. They are also used as the matrix adhesives for the production of several types of grindstones. In combination with paper, woven cotton, glass fiber, etc., components, phenolics contribute to the production of engineering and decorative laminates in the form of rods, tubes, and sheets. The sheet products Arborite and Formica are familiar as the finished surfaces of furniture, bathroom, and kitchen counter tops and other areas where attractive patterns and water resistance are important characteristics. Molded products from phenolics are also important where heat or electrical resistance is required, such as saucepan and toaster handles, switches, and the printed circuit boards used in computers. Recent phenolics production in the U.S.A. has totaled over 500,000 metric tonnes per year, not including fillers [38]. 

As can be seen in Figures I and II, the processing involves impregnating the fiberglass with the uncured epoxy resin solution, and finally fully curing layers of the prepreg with copper foil into a finished laminate. From this point the laminate is fabricated into a finished printed circuit board. 

The third problem associated with water based varnishes is poor electrical insulation properties of the laminate after moisture conditioning. This problem is probably the most critical problem because insulation failures of the laminate can lead to electrical failure of the finished printed circuit board. This property is measured by conditioning the finished laminate in a high moisture environment and then testing the dielectric breakdown strength. ED24574 has excellent insulation resistance. This was achieved by a proprietary resin composition. 

Guidelines for Waste Reduction and Recycling Metal Finishing, Electroplating, Printed Circuit Board Manufacturing... 

Removal of Heavy Metals. Federal, state and local regulations place strict limits on the quantities of heavy metals which may be released to the environment. The controlled metals include Ag, As, Cd, Cr, Cu, Pb, Hg, Ni, Sb and Zn. U.S. electroplaters, metal finishers, and printed-circuit-board manufacturers are under mounting pressure to clean up their waste waters. 

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