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1. Prototype PCB reduces side etch and bumps, improves etch coefficient

Plantar eclipse produces a sharp edge. Generally, the longer the printed board is in the etching solution, the more severe the side etch. Undercutting seriously affects the accuracy of the printed wiring. Serious undercutting will make it impossible to make fine wires. When the side etch and the edge decrease, the etch coefficient increases. A high etch coefficient indicates the ability to maintain a thin wire, making the etched wire close to the original size. Whether it is tin-lead alloy, tin, tin-nickel alloy or nickel, the overetching of the plating etching resist will cause the wire to short circuit. Because the brim easily breaks down, an electrical bridge is formed between the two points of the wire.

There are many factors that affect lateral erosion, and the following points are summarized:

(1) Etching method: immersion and bubbling etching will cause larger side erosion, and splash and spray etching will have less side erosion, especially spray etching.

(2) Types of etching solution: Different etching solutions have different chemical components, and their etching rates are different, and their etching coefficients are also different. For example, the etching coefficient of acid 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 nitric acid-based etching system can achieve almost no side etching, and the side walls of the etched lines are close to vertical. This etching system is awaiting development.

(3) Etching rate: Slow etching rate will cause severe side etching. The improvement of etching quality has a lot to do with the acceleration of the etching rate. The faster the etching speed, the shorter the time that the board stays in the etching solution, the smaller the amount of side etching, and the etched graphics are clear and neat.

(4) PH value of the etching solution: When the pH value of the alkaline etching solution is high, the side etching increases. In order to reduce side corrosion, the general pH value should be controlled below 8.5.

(5) Density of the etching solution: The density of the alkaline etching solution is too low, which will increase the side etching. It is beneficial to use an etching solution with a high copper concentration to reduce the side etching.

(6) Copper foil thickness: To achieve the etching of fine wires with minimal side etching, it is best to use thin copper foil. And the thinner the line width, the thinner the copper foil thickness should be. Because the thinner the copper foil is, the shorter the time in the etching solution, the smaller the amount of side etching.

2. Improve the consistency of the etching rate between the board

In continuous board etching, the more uniform the etching rate, the more uniformly etched the board can be obtained. To achieve this requirement, it is necessary to ensure that the etching solution is always maintained in an optimal etching state throughout the entire etching process. This requires the selection of an etching solution that is easy to regenerate and compensate, and has an easy to control etching rate.

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