Recycling of printed circuit board etching solution

Today, with the rapid development of science and technology, mankind has entered the electronic age. The extensive use of integrated circuits has brought great convenience to our work, life and learning. However, in the manufacture of some small household appliances and in China’s current basic education and teaching, some examples of chemical corrosion of printed circuit boards are also involved: small-scale home appliance manufacturers have to use traditional methods in order to continue product innovation and reduce production costs. Circuit board technology - "Chemical etching technology"; In China's current basic education, many schools in the chemical teaching process, in order to clearly reproduce the chemical corrosion of metals and chemical corrosion applications, but also the chemical corrosion of printed circuit boards As a must-do experiment. While applying knowledge to benefit society and impart knowledge, people have ignored a deep-seated problem: environmental pollution caused by printed circuit board etching fluid. In a survey of the surrounding environment of printed circuit board factories in Chengdu and nearby counties and cities (such as Sanhe Town, Xindu County), it was found that the contents of metal ions such as Cu2+ and Fe3+ in the groundwater of the circuit board factory were excessively exceeded, and the groundwater had been affected. Serious pollution. When people advocate vigorously to protect the environment, we must attach great importance to this issue and take measures to stop the further spread of this phenomenon.

Through analysis, it is known that the etching solution currently used in the manufacture of printed circuit boards is mainly an acidic solution of some high-valence metal ions (Fe3+ or Cu2+, etc.), and oxidation and reduction of the copper foil in contact with the etching liquid on the surface of the printed circuit board by oxidation-reduction reaction After entering the metal ions into the solution, so as to achieve the purpose of corrosion, the chemical reaction equation is:

2Fe3++Cu=Cu2++2Fe2+
Or Cu2++Cu=2Cu+

After use, the etching solution (containing a large amount of metal ions, Cu2+, Cu+, Fe3+, Fe2+, etc.) is discarded as a waste liquid and enters the environment via a sewer, thereby contaminating the environment.

To deal with environmental pollution, chemical workers have a long way to go. The rational use of the limited resources on the earth and the recycling of wastes are not only turning waste into treasure, but also protecting the environment. It is our goal pursued by chemical educators to impart this knowledge to future generations.

Through research, it has been found that the corrosion of printed circuit boards “waste liquid” contains a large number of metal ions that can be recycled and reused, such as Cu2+, Cu+, Fe3+, and Fe2+. According to the composition of the etching solution, a specific regeneration plan can be established. Discussed separately as follows.

1. If the corrosive solution is dissolved with solid ferric chloride in dilute hydrochloric acid and diluted with water (the concentration of ferric chloride is about 36%), then the corrosive solution is red before use. In the brown solution, the reddish-brown color of the solution became lighter (because the amount of Fe3+ ions that made the solution reddish brown was reduced), the color was darkened, and the etched copper made the solution slightly bluish by changing to Cu2+. When such corrosion fluid fails, regeneration can be achieved using the following procedure:

After batch collection, the corrosive liquid after failure is contained in a cylindrical plastic container. A few scrap iron plates of a certain length are suspended in solutions of different depths, and the solution is stirred from time to time so that the flowing solution is in full contact with the iron plate ( If the solution cannot be stirred all the time, the iron plate can be suspended in the solution for several days. Because of the replacement reaction of Fe+Cu2+=Cu+Fe2+, it can be seen that the surface of the iron plate gradually has red copper deposits (hanging on A few days later, the surface of the iron plate has "dendritic" crystal copper deposited on the surface. After a certain amount of copper is deposited on the surface of the iron plate, the iron plate is taken out and the copper is stripped for recovery. Add a small amount of iron scraps to the solution (the last and second iron scraps should be as small as possible, preferably iron powder), and add the solution while stirring so that the iron scraps are in full contact with the solution. The replacement of copper reacts as completely as possible. When the blue color of the solution disappears and it turns dark, it indicates that the displacement reaction has proceeded more completely. At this time, the main component in the solution is FeCl2. Adjust the acidity of the solution with hydrochloric acid (because iron will also consume the acid in the solution while reducing the acidity of the solution, resulting in a decrease in the acidity of the solution) and then add the appropriate concentration and appropriate amount of hydrogen peroxide solution (if a large amount of regenerated corrosive fluid, 30% should be added) Industrial hydrogen peroxide), since the redox reaction occurred: 2Fe2++2H++H2O2=2Fe3++2H2O, the etching solution was regenerated. If a certain amount of hydrogen peroxide is added, the reaction 2Fe2++2H++H2O2=2Fe3++2H2O fails to proceed, ie, the solution does not turn red (because the mark for the reaction to the end point is the characteristic color of the solution turned into Fe3+ - reddish brown) Then, the solution should be heated properly or irradiated with strong light to initiate the reaction (since the mechanism of the reaction 2Fe2++2H++H2O2=2Fe3++2H2O is a chain transfer reaction). Once the reaction is initiated, it will be completed in an instant. Finally, the concentration of the solution is adjusted with a small amount of ferric chloride solids to about 36% (monitored by a pycnometer) to obtain a red-brown ferric chloride regeneration solution. A lot of circuit board corrosion.

2. If the corrosive solution is dissolved in dilute hydrochloric acid with solid copper dichloride and then diluted with water, the corrosive solution is a dark blue solution before use and a pale blue solution after use. The Cu2++Cu=2Cu+ reaction was performed to reduce the amount of Cu2+ ions that allow the solution to be blue. The regeneration method is simpler, as long as a certain amount of hydrogen peroxide is directly added to the used "waste liquid", and the solution can be regenerated because the redox reaction 2Cu++H2O2+2H+=2Cu2++2H2O proceeds. Used for circuit board corrosion.

After the used circuit board etching solution is regenerated by the above method, it can obtain the same corrosive solution as the original function, and it is cheaper than the original solution, and it will not discharge the used corrosive waste liquid into the sewer, thus avoiding the environment. Pollution. This kind of science and technology application that can not only develop the economy, but also effectively use the limited resources on the earth, but also protect the environment is the direction that we advocate for future chemical applications.

Source: Journal Author: Emily Chevalier