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PCB manufacturing is a very complex process. There are some precautions that should be paid attention to in the PCB etching process.

1. Reduce side erosion and protruding edge and improve etching coefficient

Side erosion produces a protruding edge. Generally, the longer the printed board is in the etching solution, the more serious the side corrosion is.Side erosion seriously affects the accuracy of printed wires, and serious side erosion will make it impossible to make fine wires.When the side etching and protruding edge decrease, the etching coefficient increases. A high etching coefficient indicates the ability to keep the thin wire, so that the etched wire is close to the size of the original drawing. Electroplating etching resist, whether tin lead alloy, tin, tin nickel alloy or nickel, excessive protrusion will cause wire short circuit.Because the protruding edge is easy to break down, an electrical bridge is formed between the two points of the conductor.
There are many factors affecting side erosion, which are listed below:

1) Etching method

Immersion and bubbling etching will cause larger side corrosion, while splash and spray etching have smaller side corrosion, especially spray etching has the best effect.

2) Type of etching solution

Different chemical components of different etching solutions lead to different etching rates and etching coefficients.For example, the etching coefficient of acidic copper chloride etching solution is usually 3, and the etching coefficient of alkaline copper chloride etching solution can reach 4.Recent studies have shown that the etching system based on nitric acid can achieve almost no side etching, and the side wall of the etched line is 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 corrosion, and the etched graphics are clear and neat, which is the result of the production process of circuit board manufacturers with rich experience.

4) PH value of etching solution

When the pH value of alkaline etching solution is high, the side corrosion increases. In order to reduce side erosion, the general pH value shall be controlled below 8.5.

5) Density of etching solution

The density of alkaline etching solution is too low, which will aggravate the side corrosion. The selection of etching solution with high copper concentration is beneficial to reduce the side corrosion.

6) Copper foil thickness

In order to achieve the etching of thin wires with minimum side corrosion, it is best to use (ultra) thin copper foil. Moreover, the thinner the line width, the thinner the copper foil thickness.Because the thinner the copper foil, the shorter the time in the etching solution, and the smaller the amount of side corrosion.

2. Improve the consistency of etching rate between plates

In continuous plate etching, the more consistent the etching rate is, the more uniformly etched plates can be obtained.To meet this requirement, it is necessary to ensure that the etching solution is always in the best etching state in the whole etching process.This requires the selection of etching solution which is easy to regenerate and compensate, and the etching rate is easy to control.Select the process and equipment that can provide constant operating conditions and automatic control of various solution parameters.It is realized by controlling the amount of copper dissolved, pH value, solution concentration, temperature, uniformity of solution flow (spray system or nozzle and nozzle swing), etc.

3. Improve the uniformity of etching rate on the whole board surface

The uniformity of the etching rate on the whole board surface is determined by the uniformity of the etchant flow on the board surface.In the etching process, the etching rates of the upper and lower plates are often inconsistent.Generally speaking, the etching rate of the lower plate surface is higher than that of the upper plate surface.Because of the accumulation of solution on the upper plate surface, the progress of etching reaction is weakened.The uneven etching of the upper and lower plate surfaces can be solved by adjusting the spray pressure of the upper and lower nozzles. A common problem in etching and printing is that it is difficult to etch all the board surfaces at the same time. The edge of the board is etched faster than the center of the board. It is an effective measure to adopt the spray system and swing the nozzle. For further improvement, the etching uniformity of the whole board surface can be achieved by making the spray pressure at the center and edge of the board different and intermittent etching at the front and rear of the board.

4. Improve the ability of safe treatment and etching of thin copper foil and thin-layer pressing plate

When etching the thin-layer pressing plate such as the inner layer of multi-layer board, the plate is easy to be wound on the roller and conveyor wheel, resulting in waste products.Therefore, the equipment for etching inner laminates must ensure that thin laminates can be processed smoothly and reliably.Many equipment manufacturers attach gears or rollers to the etching machine to prevent this kind of phenomenon.A better method is to use additional left-right swinging Teflon coated wire as the support for the transmission of thin-layer pressing plate.For etching of thin copper foil (e.g. 1/2 or 1/4 ounce), it must be ensured that it is not scratched.Thin copper foil can’t stand the mechanical disadvantages like etching 1 ounce copper foil. Sometimes severe vibration may scratch the copper foil.
 
5. Reduce pollution

The pollution of copper to water is a common problem in printed circuit production, which is exacerbated by the use of ammonia alkali etching solution. Because copper is complexed with ammonia, it is not easy to remove it by ion exchange or alkali precipitation.Therefore, the second spray operation method is adopted to rinse the board with copper free additive, which greatly reduces the discharge of copper.Then, the excess solution on the plate surface is removed with an air knife before water rinsing, so as to reduce the rinsing burden of water on copper and etched salts.