What Are The Etching Methods For Printed Circuit Boards

There are 4 kinds of etching methods for printed circuit board.

1) Splash etching:

The principle of splash etching is to connect a blade or cup to the rotating shaft of a motor. When the motor rotates, the etchant is sprayed on the board under the action of centrifugal force. In other words, the contact between the board and the solution depends on the rotation of the shaft. Splash etching is better than foam etching because it etches uniformly and has less side erosion, but only a limited number of boards can be etched at a time. This etching method usually uses ferric chloride and Mingrong sulfate as etchant. Large-capacity containers are used at the bottom of the tank to reduce solution replacement. This technique is slower than automatic spray etching, so it is rarely used now.

2) Foam etching:

This technology has made some modifications in the immersion etching technology. The difference is that the gas in the air enters the etching solution. Gas plays two roles when passes through the solution:

1) Ensure that there is continuous fresh etchant on the surface to wash away the dissolved metal;

2) Improve the oxidizing ability and regenerate the etchant.

The etching speed depends on the pressure of the air. When it reaches a certain level (air pressure usually reaches 2Pa), the etching quality will be very high. This etching method uses bromide sulfate and persulfate plating as etchant. The main disadvantage of foam etching is that when hydrogen peroxide and sulfuric acid are used as the etchant, a lot of corrosive fumes will be generated. If foam etching is used, we need to collect and purify smoke effectively.

3) Immersion etching:

Immersion etching is a half-paddle technique. It only needs a tank filled with etching solution to immerse the board in the solution. The board needs to be kept immersed until the etching is completed. It requires a long etching time, and the etching speed is very slow. The etching speed can be increased by heating the etching solution. This method is suitable for small boards or prototype boards. Immersion etching usually uses sulfuric acid added with persulfuric acid plating or hydrogen peroxide as an etchant.

4) Spray etching:

The simplest form of spray etching is a box with a groove underneath. Under a pressure, the etching solution is evenly drawn from the tank through a nozzle and sprayed on the surface of the board. It sprays fresh solution on the board and has a high etching rate. The following factors determine the uniformity of etching:

1) Spray pattern, strength, consistency of spray volume and location of discharge;

2) If it is a double panel, spray on both sides.

3) The chemical properties of the etchant, the pressure of the pump, the shape of the nozzle and the placement position, these conditions determine the etching speed;

In the closed-loop recycling system, the board is continuously etched. The etching rate of this system is high, while the side etching is small and the fine line resolution is good. Due to the high yield and fine grain resolution of spray etching, it is the most widely used technology. In this technique, oxide plating etchant is often used to etch double-sided plated through-hole plates. System equipment should be made of acid or alkali resistant materials, such as PVC. However, if the system uses sulfuric acid / hydrogen peroxide as the etchant, stainless steel, polycarbonate or polypropylene is required. There are two types of spray etching technology, they are:

1) Vertical spraying: In this technique, etching is done by placing the board on a shelf so that the board can be lowered to the area of the spray box. With a large number of up and down or left and right movement of the nozzle to etch, to achieve the desired result.

2) Horizontal spraying: This technology has two rows of independently controlled nozzles at the top and bottom. Double-sided horizontal etching is usually mainly used to produce double-sided panels.

Spray etching machine can use vertical or horizontal etching in fully automatic or semi-automatic way. This automated etching involves pressure control, heating, specific gravity indicator and solution regeneration. The automatic equipment is designed to increase production speed. The board is placed on the shelf. When passing through the etching chamber, a row of nozzles swings to spray and etch the board on one or both sides, and the shelf needs to be rinsed and neutralized with water. The pressure of each row of nozzles is easy to control.

It has been proved that the rotary etching machine is very effective for the production of printed circuit board templates or a small number of printed circuit boards. In this device, the etching solution is placed at the bottom of the tank, which uses quartz heating, it can be electronically controlled to shorten the heating time and keep the temperature constant.