Abstract
Electroless copper plating is an indispensable process in the manufacture of printed wiring boards, but extraneous deposition occurs during electroless plating especially if the copper plating bath is used for a long period. Baths used for five or more truns have been found to contain more that 2×106 inorganic particles (Si, Al, Na, etc.) of from 1∼5μm leading significantly to extraneous deposition. To solve this problem, precision filtration was applied, greatly reducing the numbers of particles by continuous filtration, eliminating extraneous deposition and improving the properties of the deposited film, Furthermore, electroless deposition of copper on the filter under high speed filtration was inhibited by the use of a tapered filter instead of a wound-depth type filter.
