Bath tin/lead

The newest tin baths, tin—lead baths, and lead baths recendy entering the market, are based on methanesulfonates. The higher makeup cost of tin methanesulfonate baths, about 1.6 times the cost of fluoborate baths, may be justified where restrictions on fluoborates and boric acid in wastes exist. 

Ion chromatography is not only used to monitor the water quality, but also to analyze a variety of process liquors that are employed in the manufacture of printed circuit boards. This includes cleansers, palladium-based activators, and various electroplating baths such as acidic and electroless copper baths, tin/lead baths, electrolytical nickel baths, and gold baths. The analytical chemistry of the key substances contained in these baths is described in detail in the preceding chapter. 

Ion chromatography is used not only for monitoring the purity of water and chemicals but also for analyzing various plating baths such as acid and electroless copper baths, tin/lead baths, electrolytic nickel baths, and gold baths. The analysis of the key components in such baths will be described in more detail in Section 10.4. 

Block B shows the electrolytic copper recovery cell, which recovers metallic copper and regenerates sulfuric acid from the metal salts in the hot sulfuric acid pickle solution. It was originally felt that trace metals (zinc, tin, lead) would interfere with the recovery of pure copper. By controlling current density at 50 to 100 A/m 1 2 3, however, pure copper can be recovered while maintaining the copper concentration in the pickle bath at 15 g/L. 

In the laboratory for the electroplating facility at Molex, Inc., Lincoln, Nebraska, seventeen plating baths set up for tin and tin-lead electroplating must be tested three times daily for acid content. The procedure involves an acid-base titration using standard sodium hydroxide as the titrant. Because the volume of samples is so large, an automatic bottle-top buret is used with a 2-gal bottle filled with the standard sodium hydroxide solution. 

Two common alternatives are available for electrodepositing tin 30 alkaline and acidic baths. The alkaline bath has good throwing power but consumes more power than the acid bath. Tin is present in the alkaline bath as stannate(TV), [Sn(OH)6]2, the bath being approximately 0.25 M in free hydroxide ion (pH 13.4). The hydroxide ion is the principal charge carrier. Potassium is superior to sodium as the counter ion (greater ionic mobility) but economic factors lead to the continued use of sodium in many plants. The hydroxide ions, acting as a sink for dissolved CO2, also prevent two undesirable reactions (equations 24 and 25). 

Methane sulfonic acid is used as an electrolyte for electroplating of tin onto sheet steel, for plating tin and tin/lead alloy onto nickel or other base metal substrates in the manufacture of lead frames and bump-contacts for microelectronic devices.It can also be used for copper deposition during the manufacture of microprocessors. Other alkanesulfonic acids have also found use in electroplating applications. Disodium methanedisulfonate and other alkanedisulfonate salts are used in chrome plating.As discussed previously, several processes for the recovery and recycle of alkanesulfonic acids from spent metal plating baths have been described. 

Tin forms two stable inorganic species of Sn(II) and Sn(IV). Sn(II) is added to tin/ lead alloy plating baths. The Sn(II)/Sn(IV) ratio is important to the plating bath performance. An IC separation was carried out with the use of 0.3 mM HCl eluent [26]. Neither Sn(II) or Sn(lV) were strongly retained by the cation-exchange column used in this work. Inorganic tin speciation is quite difficult, because Sn(II) hydrolyzes easily at neutral and alkaline pH. 

Case hardening of steel using a sodium cyanide molten bath depends on the above reactions where the active carbon and nitrogen are absorbed into the steel surface. Sodium cyanide is a good reducing agent and the oxides of tin, lead, copper, or manganese are readily reduced (Kirk-Othmer, 1993). 

Agitation should be similar to tank operation—that is, vigorous air bubbhng for copper, gentle stirring for tin and tin-lead, and none for tin-nickel. Plate copper and nickel at 2 A and other metals at 1 A. The effects of bath adjustment, carbon treatment, dummy plating, and so on, are readily translated from the Hull cell to actual tank operations. See previous sections on metal plating for Hull cell results, and consult the suppher for test equipment. 

Eliminate thiourea from tin/lead stripping baths... 

Methane sulfonic acid (MSA) is a relatively expensive acid used to strip (remove) solder (tin/lead) and copper metals. This acid is also used to condition metal surfaces prior to fluo-borate free-solder electroplating when applying a final etch resist of solder onto multilayer printed circuit boards. By continuously recirculating the acid bath through a diffusion dialysis unit, a 95 percent reduction of chemical purchases (required by the process steps indicated in the first paragraph of this section) may result, producing less than a six-month return on the initial capital investment (ROI).Typically, 80 to 90 percent of the acid is recovered with 70 to 90 percent of the metals removed in an equal volume of dilute acid. 

Equally good results are obtained with cobalt baths at a dilution ratio of 10 1 and at temperatures as low as 1800°C, but iron and nickel baths, under all the conditions investigated, only gave good results at about 2100°C. The addition of tin only leads to an improvement in conjunction with iron and nickel baths. Tin and copper are unsuitable bath metals. 

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