Metal Finishing Guide Book

2012-2013

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Table VII. Neutral Cyanide Solutions Rack or Barrel Plating High-Speed Continuous Plating 8-20 80 15-30 ��� 70 6.0-8.0 160 Desired Platinum-clad columbium 1-3 90 12 min 1 oz gold/4 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 Gold as potassium gold cyanide (g/L) Monopotassium phosphate (g/L) or Potassium citrate (g/L) pH Temperature (��F) Agitation Anodes Current density (A/ft2) Current efficiency (%) Time to plate 0.0001 in. Replenishment 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) Rack or Barrel Plating, Matte Bath 2 High-Speed Continuous Plating, Bright Bath 2 8 60 ��� 8 60 0.2-0.5 8-16 90 0.7 3.8-5.0 120-140 Platinum clad Desirable 1-5 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 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 or Nickel as nickel metal (g/L) pH Temperature (��F) Anodes Agitation Current density (A/ft2) Current efficiency (%) Time to plate 0.0001 in. Replenishment The requirements for the deposit of each of these components and the methods of plating that are used are listed in Table IV. The gold plating solutions that are actually used by the electronic plater may be conveniently classified by pH range: alkaline cyanide, pH >10; neutral cyanide, pH 6 to 9; acid cyanide, pH 3.5 to 5 (below pH 3.5 the gold cyanide is generally unstable and precipitates); noncyanide (usually sulfite), pH 9 to 10. Table V lists the baths that are primarily used by the industry. Low-karat gold alloys [Group 2 or 3 (Class F)] have not found much application in the United States. The alloying metal generally affects the electrical properties of the gold adversely. As little as 1% of iron will increase the electrical resistance of gold over 1,000%, and similar amounts of other metals have less, but still unacceptable, effects on the conductivity of the gold deposit. Even amounts of alloy much less than 1% will inhibit or totally prevent good welding or die bonding of semiconductor chips to a gold surface. Duplex coatings of a low-karat gold base overplated with a highkarat gold surface, although acceptable in some applications from an electrical point of view, have tended to lose their economic advantages as good engineering and new design have required less total gold. ALKALINE CYANIDE BATHS (GROUP 1, CLASS D) Table VI lists typical alkaline cyanide baths that are still used. Note that for mat332

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