Sulfuric acid, etchant

Phosphoric acid anodizing AMPS-sulfuric acid etchant 11.8 23.5... 

Most molded plastics have a very smooth, hydrophobic surface that must be modified. Chemical etchants are used to oxidize and roughen the surface. The resultant hydrophilic surface promotes good metal-to-plastic adhesion. The etchant is usually a solution of chromic acid and sulfuric acid pure chromic acid can also be used. 

Copper etchants do not directly influence the electroless plating process, but are used merely to remove unwanted copper, and should not affect the deposit properties. The costs of waste treatment and disposal have led to disuse of throw-away systems such as chromic—sulfuric acid, ferric chloride, and ammonium persulfate. Newer types of regenerable etchants include cupric chloride, stabilized peroxide, and proprietary ammoniacal etchant baths. 

An alternative method is to use mixtures of concentrated sulfuric acid and potassium permanganate, giving contrast between crystals and amorphous domain that turns out to be applicable to many different polymers, e.g. polyethylene, polypropylene, poly(but-l-ene), polystyrene and poly(aryl ether ketone)s. The strong etchant degrades the amorphous phase more quickly than the crystals and the resulting topography is revealed by heavy metal shadowing. Replicates are prepared which are examined in the electron microscope. 

Tin Plating. Thin tin deposits (0.0002 in) are used to make SMOBC boards where the tin etch resist is stripped after etching. Alkahne ammonia etchants are usually favored. Other etchants, such as sulfuric acid-hydrogen peroxide and ammonium persulfate-phosphoric acid, have been especially formulated for bright tin. Tin plating (directly over barrier layers of nickel or tin/nickel) has been used because of its optimum solderabihty. Cupric and ferric chloride etchants attack tin and are not used. 

This section is a survey of the technology and chemistry of the copper etching systems in common use. Selection of practically available etchants has been hmited by economic, operational, and (environmental) regulatory concerns. Fabricators have been forced into practical trade-off decisions to suit situations. Two etchants in particular, chromic-sulfuric acid and ammonium persulfate, are no longer practical considerations due to environmental pressures. Other formulations and choices have been modified to suit these pressures. 

Electrolytic disposition of the copper on the surface of passivated 300 series stainless steel is one disposal method. The spent etchant is acidified with sulfuric acid prior to electrolysis. Once the copper has been removed, the remaining solution can be diluted, neutralized, checked, and discarded. The copper can be removed from the cathode. Spent sodium persulfate can be treated with caustic soda. 

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. 

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