Palladium-coated printed wiring boards - for integrated circuits, with improved solderability

• Main Authors: MIZUMOTO, SHOZO, KOBE, HYOGO, JP, UCHIDA, EI, AMAGASAKI, HYOGO, JP, NAWAFUNE, HIDEMI, TAKATSUKI, OSAKA, JP, HAGA, MASAKI, KOBE, HYOGO, JP
• Format: Patent
• Language: English; German
• Published: 23.07.1992
• Subjects: APPARATUS THEREFOR; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; CHEMICAL SURFACE TREATMENT; CHEMISTRY; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATIONOR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY IONIMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; COATING MATERIAL WITH METALLIC MATERIAL; COATING METALLIC MATERIAL; DIFFUSION TREATMENT OF METALLIC MATERIAL; ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR; ELECTRICITY; ELECTROFORMING; ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION INGENERAL; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS; METALLURGY; PRINTED CIRCUITS; PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTIONOF COATINGS; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THESURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION

A printed wiring board is disclosed, which has one or more copper conductor circuits. It has a palladium coating on at least the copper parts which are provided for mounting components by soldering. A process for the mfr. of the printed wiring board by a pattern plating process or a semi-additive process comprises: (1) forming a Cu pattern by copper electroplating; (2) depositing a Pd coating by electroless plating or Pd electroplating on to the Cu pattern parts; (3) removing the plating resist layer; (4) etching the Cu to be removed; (5) forming a soldering resist pattern. USE/ADVANTAGE - The invention is used in the mfr. of high-density integrated circuits. The Pd coating improves the solderability and protects the copper parts from contamination due to the deposition of solder. In an example, a rolled Cu foil (25 x 225 x 0.3mm) was purified by electrolysis and washed with an acid. A Pd film 0.1 thick was deposited by electroless plating, from a soln. contg. palladium dichloride, ethylene diamine, thiodiglycollic acid, and sodium hydrogen phosphite of pH 8 at 60 deg.C. The coated Cu was washed with water and dried. The solderability was tested before and after heating to 230-250 deg.C. The solderability improved by about 50% compared with a Cu sample without a Pd coaing, both before and after heating