Matters needing attention during the etching process
Reduce side etch and edge, increase etch coefficient:
Side etches can produce bumps. Generally, the longer the printed board stays in the etching solution, the more serious the side etching will be. Undercutting will seriously affect the accuracy of the printed wiring. Serious undercutting will not make fine wires. When the side etch and the protrusion decrease, the etching coefficient will increase. A high etching coefficient indicates the ability to maintain thin wires, so that the etched wires can approach the original size. Whether it is tin-lead alloy, tin, tin-nickel alloy, or nickel plating etchant, excessive lead can cause wire short circuit. Because the flange is easily torn off, an electrical disconnection is formed between the two points of the wire.
There are many factors that affect side etch. The following points are summarized.
1. Etching method: immersion and bubble etching will cause larger side erosion, while splash and spray etching will have smaller side erosion, especially the best effect of spray etching.
2. Types of etching solution: Different etching solutions have different chemical compositions, different etching rates, and different etching coefficients. For example, the etching coefficient of acid copper chloride etching solution is usually 3, while the etching coefficient of alkaline copper chloride can reach 4.
3. Etching rate: Slow etching rate will cause severe side etch. Improving the quality of etching has a great relationship with accelerating the etching rate. The faster the etching speed, the shorter the time the substrate stays in the etching, the smaller the amount of side etching, and the more clear and neat the pattern.
4. PH value of the etching solution: When the pH value of the alkaline etching solution is high, the side etching will increase. In order to reduce side corrosion, the pH value should generally be controlled below 8.5.
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5. Density of etching solution: If the density of the alkaline etching solution is too low, side etching will be aggravated. Selecting an etching solution with high copper concentration is very beneficial to reduce side etching.
6. Copper foil thickness: To achieve the etching of fine wires with minimal side etching, it is best to use (ultra) 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, and the smaller the amount of side etching.