How to use ferric chloride for etching?

Ferric chloride is a covalent inorganic compound with the chemical formula FeCl3. It is a black-brown crystal, and also has a flake shape, with a melting point of 306°C and a boiling point of 316°C. It is easily soluble in water and has strong water absorption. It can absorb moisture in the air and deliquescence. When FeCl3 is precipitated from the aqueous solution, six crystal waters are FeCl3 6H2O, and ferric chloride hexahydrate is an orange crystal. Ferric chloride is an important iron salt.

The discovery of FeCl3 etching principle:

Fecl3 etching is one of the earliest processing methods used for copper and gold etching. This method is easy to obtain raw materials, cheap, simple to prepare and easy to operate. Therefore, this method has been widely used, even now. Used by more copper etching plants. However, this method has serious environmental pollution and is gradually replaced by other corrosion methods.

Introduction of FeCl3 etching principle:

(1) Influence of FeCL3 concentration on etching rate: With the increase of FeCL3 concentration in FeCL3 etching solution, the etching rate is accelerated. When the FeCL3 contained exceeds a certain concentration, the etching rate will decrease due to the increase of solution viscosity.

(2) The effect of the addition amount of hydrochloric acid on the etching rate: adding hydrochloric acid to the etching solution can firstly inhibit the hydrolysis of FeCL3 and CuCL2; secondly, it can increase the etching speed. Especially when the copper content in the etching solution reaches 37.4g/L, the effect of hydrochloric acid is more obvious.

(3) The effect of temperature on the etching rate: In the FeCL3 etching process, with the increase of temperature, the etching rate is also accelerated. For example, when the temperature is 50 degrees, the etching rate of copper by the new etching solution can reach 10um/min. But in actual production, room temperature etching method is used. The etching of copper by FeCL3 is an exothermic reaction. As the etching proceeds, the temperature of the etching solution will gradually increase, and the etching speed will be accelerated. As FeCL3 is consumed, the etch rate decreases. At the same time, the temperature rise process is relatively slow, so the etching rate does not change much during the entire etching process.

(4) The influence of stirring on the etching speed: the speed and etching quality of static etching are relatively poor. This is because in the etching process, on the one hand, there will be precipitates on the etched copper surface and in the etching solution, which affects the normal etching of copper; on the other hand, during the copper etching process, the solution on the etched surface will gradually appear dark green. , which indicates that FeCL3 on the etched surface has undergone a reduction reaction with the copper surface and lost its oxidizing ability.

Cu+FeCI3-CuCl+FeCl2

CuCl ions have reducibility, and further react with Fe3+ in the etching solution to form CuCl.

CuCl+FeCl3-CuCl2+FeCl2

The resulting CuCl2 is oxidizing and will also undergo redox reactions with copper.

Cu+CuCl2-2CuCl

FeCl3 etching principle conclusion:

FeCl3 etching solution is completed by FeCl3 and CuCl2 at the same time. Among them, the oxidation ability of n is strong, and the etching speed is fast. The etching quality is good. Relatively speaking, CuCI2 has a slow etching speed and poor etching quality here. With the consumption of Fe3+ in the etching solution and the increase of CuCl2, the etching speed is gradually slowed down and the etching quality is deteriorated. When the consumption of Fe3+ reaches 50%, the etching speed and etching quality will be unfavorable to continue the etching process. Instead, replace the etchant.

In actual production, the etching efficiency of the etching solution is not measured by the consumption of Fe3+, but by the dissolved copper in the etching solution (unit: g/l). Copper in FeCl3 etching solution, the initial etching rate is constant. However, with the consumption of Fe3+ in the etching solution, the copper content in the etching solution increases continuously. When the amount of dissolved copper reaches 60g/L, the etching speed will slow down. When the consumption of Fe3+ in the etching solution reaches 40% or the amount of dissolved copper When it reaches 83g/L, the etching rate will drop sharply. At this time, the etching solution can no longer be used, and the regeneration or renewal of the etching solution should be considered.

The acidity of the FeCl3 etching solution usually used is not high, so when the FeCl3 etching solution is etching copper, it is also accompanied by the hydrolysis side reactions of FeCl3 and CuCI2:

FeCl3+3H2O-Fe(OH)3+3HCI

CuCl2+2H2O-Cu(OH)2+2HCl

The generated oxychloride is unstable and easily decomposed into corresponding oxides and water when heated. Some of these oxides are precipitated at the bottom of the etching tank to form loess-like deposits, and some are suspended in the etching solution, which has a certain destructive effect on the anti-corrosion layer:

2Fe(OH)3-Fe2O3+3H2O

Cu(OH)2-CuO +H2O