Corrosion principle and composition of alkaline CuCl2 in etching machine

Alkaline etching solution is generally suitable for the production of outer circuit patterns on multi-layer printed boards. This etching method is widely used in circuit board production, especially in pattern electroplating, which is one of the better etching methods. At the same time, alkaline etching has a fast etching speed, small side etching, and a large amount of copper dissolution. The etching solution can be regenerated and continuously used.

The alkaline CuCl2 etching solution is mainly composed of CuCl2 and NH3-H2O. Adding NH3-H2O to the CuCl2 solution will cause the following complexation reaction: CuCl2 4NH3-H2O＝[Cu(NH3)4]Cl2 4H2O, stay Etching machine Inside the medicine box, copper is oxidized to Cu by the [Cu (NH3) 4] 2 complex ion. The oxidation reaction is as follows: [Cu(NH3)4]Cl2 Cu＝2[Cu(NH3)2]Cl。 The generated [Cu (NH3) 2] is a complex ion of Cu, which does not have oxidation ability. In the presence of excess NH3-H2O and Cl -, it can be quickly oxidized by oxygen in the air, producing [Cu (NH3) 4] 2 with etching ability. The regeneration reaction of its complex ions is as follows:

2 [Cu (NH3) 2] Cl 2NH4Cl 2NH3-H2O 1/2O2=2 [Cu (NH3) 4] Cl2 2H2O.

From the chemical equation above, it can be seen that Etching machine During the work process, for every 1 mol of copper corroded, 2 mol of NH3-H2O and 2 mol of NH4Cl are required. Therefore, during the etching process of the corrosion machine, NH3-H2O and NH4Cl should be continuously replenished as copper dissolves.

In alkaline vacuum Etching machine The concentration of Cu2 in the solution, pH value, NH4Cl concentration, NH3-H2O concentration, and temperature all affect the etching efficiency. Mastering the influence of these factors is necessary to effectively control the solution and maintain a constant optimal etching state, thereby achieving satisfactory etching quality. Based on our years of practical experience, the following conclusions have been drawn for reference only:

(1) The effect of Cu2 concentration on etching rate: In this etching solution, Cu2 is an oxidant, so the concentration of Cu2 has an impact on the etching rate Etching machine The influence of etching speed plays an important role. Practical experience tells us that the etching rate is very slow when the concentration of Cu2 is between 0g/L and 82.5g/L; The etching rate is low and difficult to control at 82.5g/L~135g/L; At 135g/L~165g/L, the etching rate is high and the solution is stable; At 165g/L~225g/L, the solution is unstable and tends to precipitate.

(2) The influence of pH value in etching solution on etching rate: The pH value of the etching solution should be maintained between 8 and 8.8. When pH<8, on the one hand, it is unfavorable for the metal corrosion-resistant layer, and on the other hand, copper in the etching solution cannot fully form copper ammonia complex ions, resulting in precipitation of the solution and difficulty in etching. If the pH value of the chemical solution is too high, the ammonia in the etching solution will be supersaturated, and free ammonia will be released into the atmosphere, causing environmental pollution. At the same time, the high pH value of the chemical solution will also increase the amount of lateral corrosion, thereby affecting the etching accuracy.

(3) The effect of NH4Cl concentration on etching: From the chemical reaction equation of solution regeneration, it can be seen that the regeneration process of [Cu (NH3) 2] - requires the presence of a large amount of NH3-H2O and NH4Cl. If Etching machine Lack of NH4Cl in the medicinal solution will prevent the regeneration of [Cu (NH3) 2] -, resulting in a decrease in etching rate and loss of etching ability. So, the content of NH4Cl has a significant impact on the etching rate. However, excessive Cl - content in the solution can cause erosion of the corrosion-resistant layer, and the concentration should generally be controlled at around 150g/L.

(4) The effect of temperature on etching rate: When the etching temperature is below 40 ℃, the etching rate is very slow, and a too slow etching rate will increase the amount of side etching and affect the etching accuracy. When the temperature is higher than 60 ℃, the etching rate is significantly accelerated, but the volatilization of ammonia also greatly increases, leading to environmental pollution and an imbalance in the proportion of chemical components in the solution. Therefore, generally Etching machine It is advisable to control the working temperature between 45 ℃ and 55 ℃.