Copper etchant

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. 

Copper Etchant Baths. One of the most promising applications of coupled transport is the renovation of circuit board etchant solutions that contain copper.61 The printed circuit board industry produces more than ten million gal-lons/year of spent etchant solutions in which copper, other salts and etchant chemicals are concentrated. Coupled transport permits continuous on-site removal of copper from the etchant solutions and simultaneous regeneration of the etchant solution. This represents a considerable savings in the costs of manufacturing circuit boards. 

Gold. With an underplate of nickel or tin/nickel, gold provides excellent resistance to ah the common copper etchants. Some etchants have a slight dissolving effect on gold. 

The preceding factors serve to evaluate copper etchants to be used. Introduction, chemistry, properties, and problems are given in this section, along with suggestions for selection and control. 

F. Gorman, Regenerative Cupric Chloride Copper Etchant, Proceedings of the California Circuits Association Meeting, 1973 Electronic Packaging and Production, January 1974, pp. 43-46. 

Perhaps the most versatile of the copper etchants is the hydrogen per-oxide/sulphuric acid mixture, although these solutions require stabilizers to retard the spontaneous minpc liofi of peroxide to water and oxygen. The r ons occuring during etching are ... 

For the more complex alloys anodic polarisation offers a vital extra variable in the use of selective etchants and has been widely exploited for alloys for which simple chemical etchants have proved inadequate. Besides many types of alloys steelthis technique has been applied to copper and the Cu-Be-Ni-Zr alloys " , uranium-base alloys " , Ni-Al alloys , tin-bearing invar and many others. 

Recovery of Copper from Printed Circuit Board Etchant... 

This process was enabled by the development of a suitable cell-dividing material a process development where the excess etchant is pumped to the recovery circuit and the copper is obtained in a recoverable form. 

In the etching procedure, copper concentration is continuously increased by the etching and, to keep the etching efficiency constant and optimal, spent etchant has to be withdrawn and replaced with fresh etchant (replenisher). An alternative would be to remove a part of the copper content from the spent etchant, without changing the other conditions in the solution, in such a way that the barren etching solution can be recycled. This process is called the MECER process [2,25]. 

Recovery of Toxic Copper from Printed Circuit Board Etchant for Reuse at Praegitzer industries, Inc., Dallas, Oregon, United States... 

Gluconates and glucoheptonates are essential components of many alkaline rust removers and cleaners, paint strippers, and etchants. They frequently cause complexation of dissolved heavy metals such as copper, nickel, and zinc. Conventional sodium hydroxide treatment does not result in sufficient precipitation of these complexed metals to meet EPA standards. In tests performed by Srinivasan (1983), the use of lime or calcium hydroxide proved far better. In particular, lime treatment resulted in more metal removal, better flocculation and faster sludge settling, and could also be used in conjunction with sodium hydroxide treatment. 

Raw materials for PC board manufacture that contain metals include the following o Copper foil (encasing the board) o Etchants chromic acid, cupric chloride, ferric chloride o Catalysts stannous tin, palladium chloride o Electroless copper bath copper sulfate... 

Chromium from the etchant and copper from the boards are typical contaminants in spent etchant solution and rinse water. 

Cupric chloride (CuClj) ia a strong etch employed for producing circuit patterns on the board. The etchant loses its effectiveness as copper etched from the board reduces the CuClj to cuprous chloride (CuCl). The spent etchant can be regenerated, however, by oxidizing the CuCl, using direct chlorination (DHS 1987). 

---