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Using Barcode encoder for Software Control to generate, create Denso QR Bar Code image in Software applications. Use of Nonproprietary Chemistry to Avoid Chelating Agents. Chelating agents are molecules that form a charged complex with a metal ion such as copper. They are used to enhance solubility and keep the metal ions in solution. Typical chelating agents used in printed circuit board fabrication include ferrocyanide, ethylenediaminetetraacetic acid (EDTA), phosphates, and ammonia. Chelated baths are intended to enhance etching, cleaning, and electroless plating but make waste treatment much more difficult because the metals are tightly bound in the complex, which inhibits precipitation. Often ferrous sulfate must be added to wastewaters to break the chelators prior to precipitation of metal hydroxides. The iron is precipitated as well as other metals, thus increasing the amount of sludge produced. Use of nonchelated chemistry where possible will eliminate this problem. If some chelating chemistry is required in the process, proper waste segregation should be implemented to minimize the volume of any chelated waste streams.
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Copper Sulfate Crystallization Theory of Operation. The sulfuric acid/hydrogen peroxide etching reaction is: Cu + H2O2 + H2SO4 CuSO4 + 2H2O >> Systems employing crystallizers are designed to 1. Lower the solution temperature to lower the solubility of copper. 2. Then remove copper in the form of copper sulfate pentahydrate crystals (CuSO4 5H2O). 3. Then reheat the bath (to prevent copper from clogging the return pipe line if the bath temperature is lowered further) before transferring the bath back to its working tank. An advantage, from a waste treatment point of view, is that the bath is recycled and not routinely dumped. Other microetchants must be dumped when the copper concentration increases. The most significant advantage, from a process point of view, is that a low copper concentration can be maintained and the printed circuit board factory will minimize its purchase of microetchant chemicals. A disadvantage to this process is that, at the time of this writing, there are no outlets available to receive and recycle the crystals, so the only alternative for manufacturers using crystallizers is to dissolve the copper sulfate crystals in spent dilute (10 percent) sulfuric acid. After the copper has dissolved, this material can be pumped to another holding tank for recirculation through an electroplating cell for reclaim of the copper. (60.1)
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Rinse Water Recycling Rinse waters can be treated and reused in the process. This can be accomplished in two ways. Rinse water recycling can be accomplished with a point-of-source system. In this system, the flow from selected rinses is recirculated through cation and anion exchange columns and then returned to the point of origin. It may be necessary to add a carbon filtration step for rinses containing organics. The second method would involve a central system. Selected rinses could be run through an ion exchange system for copper removal. Following this step, these rinses would pass through a general resin for cation removal, a general resin for anion removal, systems for organic removal such as activated carbon, ozonation or UV peroxide, and final filtration. In some cases, reverse osmosis could be substituted for the general ion exchange steps. Given the complexity of this treatment process, it would be cost-effective only for large printed circuit board facilities with high water use rates.
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Copper Recovery via Electrowinning Theory of Operation. Electrowinning is the reduction of copper ions to solid metallic copper at a cathode. The following are the chemical reactions governing copper recovery in an acidic solution. The reduction reactions that occur at the cathode are: Cu+2 + 2e Cu (metal) >> >> 2H + 2e H2 (gas)
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(60.2) (60.3)
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The reaction that occurs at the anode is: H2O 1 2(O2) + 2H+ + 2e >> (60.4)
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The first reaction describes the principal objective of electroplating (the reduction of copper to its solid form on the cathode). As electroplating proceeds, the waste becomes more acidic, as noted in Eq. 60.4. The speed of these reactions will be inhibited if oxidizing chemicals are present. Typical oxidizing agents include peroxides and persulfates, which are normal components of microetching baths. If these oxidizers are not chemically reduced in the solution entering an electroplating module, additional reaction time must be anticipated to reduce the oxidizers electrically. Following that, the reduction of copper will occur. For this reason, a chemical reduction step (addition of sodium bisulfite (NaHSO3) or sodium metabisulfite (Na2S2O5) is recommended before the waste is recirculated through an electroplating module. sources: 1. 2. 3. 4. 5. Central Systems. Copper can be recovered in a central system from the following
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Sulfuric acid regeneration of selective cation columns Spent microetch baths Dragout tanks Copper sulfate electroplating bath bailout Dissolved copper sulfate crystals from a crystallizer
The typical concentration of the preceding mixture (or any component of it) may range from 5 to 30 g of copper per liter. A central electrowinning system is shown in Fig. 60.4. Parallel Plate Electrowinning Systems. The purpose of parallel plating, in a central system, is to recover copper as a 99.9 percent pure metal sheet (for resale) and to reduce the copper concentration in the liquid being recirculated to 1.0 g/l, or less.The efficiency of the reaction drops significantly below 1.0 g of copper per liter, as observed by the generation of heat in the bath by the electroplating process. Many factors affect the ability of an electrolytic cell to recover copper. Important design parameters center around improving the mass transport. These include solution agitation and cathode agitation. Air agitation of the waste within the electroplating cell is used to increase the efficiency of the cell. Control of the air inlet rate, bubble size, current density and distribution are all critical to maintaining high efficiency in each parallel plate cell. Particles (so-called dendrites) or fines of metal can be dislodged and accumulate in dead spots with the plating cell tank. Electrical shorting out of the anode to cathode can occur when particles accumulate, creating the possibility of isolated locations where burning of the cell may occur. High-Surface-Area Electrowinning Systems (HSA). HSA systems can be used to recover copper from a variety of solutions, including electroless copper concentrates and rinses. The use of high-surface-area cathodes improves the mass transport characteristics over flat plate cathodes. The HSA cathodes reduce electrode polarization potential and improve
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