PCB News - PCB board production etching process

PCB board production etching process

PCB board production and etching process is divided into: stripping film, circuit etching, stripping tin (lead). Here is a detailed introduction to these three processes:
PCB etching
Peeling
In PCB board production, only 2 steps will use peeling film. D/F stripping after the inner layer circuit is etched and D/F stripping before the outer layer circuit is etched (if the outer layer is produced as a negative film process). The stripping process of D/F is simple, all of which are connected with horizontal equipment, and the chemical liquids used are mostly NaOH or KOH with a concentration of 1 to 3% by weight.

1. Institutions that etch copper

(1) Copper ions are easy to form copper hydroxide precipitation in alkaline environmental solutions. In order to prevent this precipitation phenomenon, it is necessary to add enough ammonia water to produce copper ammonia complex ion groups to inhibit precipitation. It can also allow the original large amount of copper and the copper that continues to be dissolved to form a very stable copper ammonia ions in the liquid. Such divalent ammonia copper complex ions can be used as an oxidant to oxidize and dissolve zero-valent copper, but monovalent cuprous ions are generated during the oxidation-reduction reaction.

In this reaction, the solubility of cuprous ions is very poor, and it needs to be oxidized into soluble divalent copper ions with the assistance of ammonia, ammonia ions and a large amount of oxygen in the air, and then it becomes an oxidant that corrodes copper, and continues to corrode copper. Until the amount of copper slows down too much. Therefore, in addition to removing the ammonia odor, the general etching machine can supply fresh air to accelerate the corrosion of copper.

(2) In order to make the above-mentioned copper etching reaction proceed more quickly, more additives are added to the etching solution, such as:

A. Acceletator can promote the above-mentioned oxidation reaction more quickly and prevent the precipitation of cuprous zirconium ions.

B. Banking agent (Banking agent) to reduce lateral erosion.

C. Suppressor suppresses the scattering of ammonia at high temperatures, inhibits the precipitation of copper and accelerates the oxidation reaction of copper.

2. Equipment

(1) In order to increase the corrosion rate, it is necessary to increase the temperature to above 48 degree Celsius, so there will be a large amount of ammonia odor diffused and proper ventilation will be required, but when the ventilation rate is too strong, a large amount of useful ammonia will also be evacuated and waste. Appropriate throttle valve can be added in the exhaust pipe for control.

(2) The etching quality is often limited due to the pudding effect. (Because the fresh liquid medicine is blocked by the accumulated water, it cannot be effectively called the pool effect with the copper surface reaction). This is why the front part of the PCB board often has an over etch phenomenon Therefore, the following points need to be considered in equipment design:

a. The thinner circuit side of the board is facing down, and the thicker circuit side is facing up.

b. The upper and lower spray pressure of the nozzle is adjusted as compensation, and the difference is adjusted according to the actual operation result.

c. The advanced etching machine can control when the circuit board enters the etching section, the first few groups of nozzles will stop spraying for a few seconds.

d. A vertical etching method is designed to solve the problem of unevenness on both sides, but it is rarely used in China.

3. Add control

Automatic replenishment of the replenishing liquid is ammonia water, usually based on extremely sensitive specific gravity, and sensing the current temperature (due to the difference in specific gravity at different temperatures), set the upper and lower limits, start adding ammonia when the upper limit is exceeded, and stop until it is lower than the lower limit. At this time, the position of the detection point and the position of the nozzle where the ammonia is added are very important, so as to avoid the waste of adding too much ammonia due to the detection delay (because it will overflow).

4. Daily maintenance of equipment

(1) Do not let the etching solution have sludge (light blue monovalent copper sludge), so the composition control is very important, especially the pH, which may be caused by too high or too low.
(2) Keep the nozzle not blocked at all times. (The filtration system should be kept in good condition)
(3) The specific gravity induction adding system should be checked regularly.

The step of stripping tin (lead) is purely processing and has no added value. However, in order to ensure the quality of the product, you still need to pay attention to the following points:

(1) The tin (lead) stripping solution is usually two-liquid or single-liquid type provided by the supplier. The stripping methods are semi-soluble and fully soluble. The solution composition is fluorine/H2O2, HNO3/ H2O2 and so on.
(2) Regardless of the formula, the following potential problems may occur during operation:
A. Attack the copper surface
B. Process after stripping the unfinished effects
C. Waste liquid treatment problem
PCB board production etching process

In order to ensure the stable quality of the product, stripping tin (lead) requires good equipment design and pre-process tin (lead) thickness control and liquid drug efficacy management. How to judge the quality of etching? It is mainly based on the following points:

1. a sharp edge
2. Side erosion
3. Etching coefficient factor
4. Over-eclipse
5. Etched surface finish
6. Is the line spacing clear?

Through the introduction of the PCB etching process above, I believe everyone will have a new understanding of PCB etching.

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