Metal Finishing Guide Book


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Table V. Electronic Gold Plating Solutions Alkaline Cyanide Neutral Cyanide Acid Cyanide Noncyanide Semiconductors Class D Class D ��� ��� Printed circuits ��� ��� Class E ��� Class E ��� Class E ��� Connectors Table VI. Alkaline Cyanide Baths Matte Gold as potassium gold cyanide (g/L) Silver as potassium silver cyanide (g/L) Dipotassium phosphate (g/L) Potassium cyanide (g/L) pH Temperature (��F) Anodes Anode/cathode ratio Agitation Current density (A/ft2) Rack Barrel Current efficiency (%) Time to plate 0.0001 in. Replenishment Bright 8-20 ��� 22-45 15-30 12 120-160 Stainless steel 1:1 Moderate to vigorous 8-20 0.3-0.6 ��� 60-100 12 60-80 Stainless steel 1:1-5:1 None to moderate 3-5 1-2 90-95 8 min at 5 A/ft2 1 oz gold/4 A-hr 3-8 1-2 90-100 7 min at 6 A/ft2 1 oz gold/4 A-hr 1. ���Burn on��� a dark smutty finish. 2. Relieve the highlights on a deeply recessed piece or the flat surface on a filigreed piece by either hand rubbing with pumice and sodium bicarbonate or wheel relieving with a cotton buff, tampico brush, or a brass or nickel-silver wheel. Other methods are possible. 3. Flash gold or a gold alloy deposit on the imperfectly cleaned highlights. Typical formulations for antique gold baths are provided in Table II. The more the solutions in Table II are abused and the more the operator violates good plating practice and good cleanliness the better and more distinctive the finish will be. An expensive finish requiring double-racking, but a beautiful finish, is Russian antique. This may be produced by relieving the green-gold antique in Table II and then flashing over with the 24K or English gold. The old antique baths of the 1940s and 1950s that did not require double-racking or stringing are no longer practical because of the high price of gold. HEAVY DECORATIVE GOLD (CLASSES C-1 AND C-2) It is necessary to distinguish between the actual karat assay of a gold alloy electroplate and the apparent karat color of the plate. In general a decorative karat deposit will appear to be a much lower karat than it actually will assay. A 14K color deposit may actually assay 20 to 21K. The formulas in Table III will deposit karat colors but will actually assay a higher karat. (In computing costs it is best to assume that the deposit is pure gold.) INDUSTRIAL/ELECTRONIC GOLD PLATING Gold is electroplated for many different electrical and electronic purposes; however, today the majority of gold plating is applied to three specific classes of components: semiconductors, printed/etched circuits, and contacts/connectors. 331

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