Hydrochloric acid etchant

Then the samples were rinsed in distillated water at 40 C with further rinsing in the running de-ionized water and drying at 90-95°C in an oven. The masking layer was removed from the back side and the rest of aluminum foil was etched in the etchant consisted of hydrochloric acid and copper chloride to get free-standing films of porous alumina. We found that the additional removal of alumina bottoms in pores can be reasonable to get hollow cylindrical pores throughout the sample. 

The conventional method to recycle acid cupric chloride etchants consists in an addition of hydrochloric acid and hydrogen peroxide. Thus, the volume of the etchant is continuously growing and it has to be discarded partly. Many attempts have failed to find a solution for the electrolytic treatment even with the use of membranes. The main reason consists in the evolution of toxic chlorine at the anodes as soon as mass transfer becomes limited at high anodic current densities. 

This process is more complicated because both hydrogen peroxide and hydrochloric acid add water in the reaction process. Since hydrogen peroxide is unsafe to store and handle in concentrations above 35 percent, there is considerable water added with both the oxidizer and the hydrochloric acid. The result hmits the copper-holding capacity of the etchant. The addition is reasonably and simply controlled as a direct ratio of HCl, and peroxide is added to the bath to maintain the copper oxidation. This formulation has been favored in Europe and to some extent in Asia. 

Chlorination. Direct chlorination has been the preferred technique for regeneration of cupric etchant because of its historically low cost, high rate, efficiency in recovery of copper, and pollution control. The cupric chloride-sodium chloride system (Table 34.1, no. 3) is suitable. Figure 34.2 shows a generalized process. Chlorine, hydrochloric acid, and sodium chloride solutions are automatically fed into the system as required. Sensing devices include oxidation-reduction instruments (Cu oxidation state), density (Cu concentration), level sensors. 

The etchant is a solution of cupric chloride and hydrochloric acid (Table 34.1, no. 1). Etchant flows continuously between spray-etching machines and a plating tank. In the plating machine, two processes take place simultaneously copper is plated at the cathode, and regeneration of the spent etchant occurs at the anodes. pf>er recovery may not return copper value and may be expensive, inconvenient, and cause difficulty with recycling. 

The methods previously described are adaptable to image transfer and etching of nickel-based materials. Etching uses ferric chloride (42° Baume) at about 100°E Other etchants include solutions made from one part nitric acid, one part hydrochloric add, and three parts water, or one part nitric add, four parts hydrochloric acid, and one part water. 

Hydrogen peroxide can be combined with vinegar and table salt to form a substitute for industrial chemicals such as ferric chloride, ammonium persulfate, or hydrochloric acid as a hobbyist s printed circuit board etchant. 

Although there is considerable evidence that chemical surface treatments improve the substrate bondability of stainless steels, there is no general agreement on which is the best. One etchant commonly used with stainless steels is an HNO3-HF mixture [128-131] others are chromic acid and ferric chloride/hydrochloric... 

Precleaning for resist appUcation includes nonetch alkaline soak, water rinsing for 5 to 10 s in chromic-sulfuric acid, rinsing, and drying. Preferred etchants include ferric chloride (12 to 18° Baume), sodium hydroxide (5 to 10 percent), inhibited hydrochloric add, phosphoric acid mixtures, solutions of HCl and HF, and ferric chloride-hydrochloric add mixture. 

Applied by still-bristle brush. Acid should be prepared in a polyethylene pail 10-12% hydrochloric or sulfuric acids are alternative etchants. 

Several pretreatments are recommended by the British Standards Institute [66]. In essence, these methods cover solvent and/or alkaline degreasing followed by surface abrasion or by the use of a chemical etchant. Grit blasting, using chiU-cast iron shot, glass or alumina, is the ideal abrasion technique. Etchants based on sulphuric, hydrochloric or phosphoric acid are recommended etching conditions are 5-30 min at temperatures from ambient to 65°C. 

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