Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Table VII. Neutral Cyanide Solutions Rack or Barrel Plating 8-20 Gold as potassium gold cyanide (g/L) Monopotassium phosphate (g/L) or Potassium citrate (g/L) pH Temperature (° Agitation Anodes F) Current density (A/ft2 Current efficiency (%) Time to plate 0.0001 in. Replenishment ) 70 6.0-8.0 160 Desired Platinum-clad columbium 1-3 90 12 min 1 oz gold/4 A-hr Table VIII. Acid Cyanide Plating Solutions Barrel Plating, Matte Bath 1 Gold as potassium gold cyanide (g/L) Citric acid (g/L) Cobalt as cobalt metal (g/L) or Nickel as nickel metal (g/L) pH Temperature (° Anodes Agitation Current density (A/ft2) Current efficiency (%) Time to plate 0.0001 in. Replenishment F) 8 60 — 3.8-5.0 120-140 Platinum clad Desirable 1-5 Rack or Barrel Plating, Matte Bath 2 8 60 0.2-0.5 3.8-4.5 70-90 Platinum clad or stainless steel Desirable 5-20 30-40 10 min at 10 A/ft2 1 oz gold/12 A-hr 90 4.5-5.5 120-160 Violent Platinum-clad columbium 100-400 95-98 10-20 sec 1 oz gold/4 A-hr High-Speed Continuous Plating, Bright Bath 2 8-16 90 0.7 3.8-4.3 70-120 Platinum clad Violent 100-400 30-40 15 sec at 400 A/ft2 1 oz gold/12 A-hr per gallon of solution. (4) Mix for no longer than 20 to 30 min. (5) Filter the solution by decantation back into the original tank. No general rule can be given for the frequency of carbon treatment. This will depend on general cleanliness and housekeeping as well as the work being processed; however, it will vary from once every two weeks to once every two months. The room temperature bright bath will require much less carbon treatment than the hot cyanide bath. NEUTRAL CYANIDE SOLUTIONS (GROUP 2, CLASS D) The neutral cyanide baths are primarily used by the semiconductor industry. Considerable care must be exercised to prevent contamination of the solution because even a few parts per million of undesirable inorganics can cause the deposit to fail in compression or die bonding. Typical nonproprietary solutions are listed in Table VII. Pulse plating may be used to advantage with the high-speed formulation. Most effective is a 10% duty cycle. Proprietary baths add grain refiners that decrease porosity, increase the maximum allow- able current density, decrease grain size, and generally improve the appearance of the deposit. ACID CYANIDE PLATING SOLUTIONS (GROUP 3, CLASS E) Table VIII lists typical acid cyanide plating solutions. Note that pulse plating can be applied with the high-speed bath, but is not widely used. 219 80 High-Speed Continuous Plating 15-30 —

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