The process of printed circuit board from light board to showing circuit diagram is a relatively complicated physical and chemical reaction process. This paper will focus on its final step--Etching for analysis. Currently, printed circuit boards (PCB)
The typical process of processing adopts 'graphic electroplating method '.
That is, firstly, a layer of lead-tin anti-corrosion layer is pre-plated on the copper foil part to be reserved on the outer layer of the board, that is, the graphic part of the circuit, and then the rest of the copper foil is chemically corroded, which is called etching.
Etching method is a method of removing copper foil other than conductive lines with etching solution. Engraving method is a method of removing copper foil other than conductive lines with engraving machine. The former is a chemical method, which is more common, the latter is a physical method.
The circuit board etching method is a chemical etching method, which is a circuit board made of copper coating that is not needed by concentrated sulfuric acid corrosion.
The engraving method uses physical methods, special engraving machines and cutter heads to carve copper clad plates to form circuit wiring.
Understand the problems that should be paid attention to during PCB etching.
Reduce side erosion and protruding edge, improve etching coefficient, and generate protruding edge by side erosion.
Generally, the longer the printed board stays in the etching solution, the more serious the side erosion is.
Side erosion seriously affects the precision of printed wires, and serious side erosion will make it impossible to make fine wires.
When the side corrosion and the protruding edge decrease, the etching coefficient increases. A high etching coefficient indicates the ability to maintain thin wires, so that the etched wires are close to the size of the original drawing.
Electroplating etching resists, whether tin-lead alloy, tin, tin-nickel alloy or nickel, will cause short circuit of wires.
Because the protruding edge is easy to break down, an electrical Bridge is formed between two points of the conductor. The influencing factors of lateral erosion are as follows!
1. Etching method: soaking and bubbling etching will cause large side erosion, while splashing and spraying etching will cause small side erosion, especially spraying etching has the best effect.
2. Types of etching solutions: different etching solutions have different chemical compositions, and their etching rates and etching coefficients are different.
For example, the etching coefficient of acidic copper chloride etching solution is usually 3, and that of Alkaline copper chloride etching solution can reach 4.
Recent studies have shown that nitric acid-based etching systems can achieve almost no side corrosion, and the side walls of the lines that reach etching are close to vertical. This etching system is yet to be developed.
3. Etching rate: slow etching rate will cause serious side corrosion.
The improvement of etching quality is closely related to the acceleration of etching rate.
The faster the etching speed, the shorter the time the board stays in the etching solution, the smaller the amount of side etching, and the clear and neat the etched figure.
4. PH value of etching solution: when the pH value of alkaline etching solution is higher, lateral Corrosion increases.
In order to reduce lateral erosion, the general pH value should be controlled at 8. Below 5.
5. Density of etching solution: If the density of alkaline etching solution is too low, side erosion will be aggravated. Selecting etching solution with high copper concentration is beneficial to reduce side erosion.
6, copper foil thickness: to achieve the minimum side corrosion of thin wire etching, it is best to use (Super)Thin copper foil. And the thinner the line width, the thinner the thickness of the copper foil.
Because the thinner the copper foil, the shorter the time in the etching solution, the smaller the amount of side erosion.
Maintenance of etching equipment the most critical factor in the maintenance of etching equipment is to ensure that the nozzle is clean and there is no obstruction to make the spray smooth.
Blockage or slagging will impact the layout under the action of injection pressure.
If the nozzle is not clean, it will cause uneven etching and scrap the whole PCB.
Obviously, the maintenance of the equipment is to replace the damaged and worn parts, including the replacement of the nozzle, which also has the problem of wear.
In addition, the more critical problem is to keep the etching machine free from slagging, and slagging accumulation will occur in many cases.
Excessive accumulation of slagging may even affect the chemical equilibrium of etching solution.
Similarly, if there is excessive chemical imbalance in the etching solution, the slagging will become more serious. The problem of slag accumulation cannot be overemphasized.
Once a large amount of slagging occurs suddenly in the etching solution, it is usually a signal that there is a problem with the balance of the solution.
This should be properly cleaned with strong hydrochloric acid or supplemented with the solution.
Residual film can also produce slags, and a very small amount of residual film is dissolved in etching solution to form copper salt precipitation.
The slagging formed by the residual film indicates that the previous film removal process is not complete.
Poor film removal is often the result of the combination of edge film and electroplating.
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