With the development of the PCB industry, the impedance requirements of various wires are getting higher and higher, which inevitably requires stricter control of the width of the wires. The etching process is very important, and it is also an indispensable process in the pcb industry. The following pcb factory introduces what is circuit board etching and six factors that affect side etching.
Introduction to pcb circuit board etching
The process of the circuit board from the light board to the display of the circuit pattern is relatively complicated. At present, the typical process of circuit board (PCB) processing adopts the “pattern electroplating method”, that is, first on the copper foil part that needs to be retained on the outer layer of the circuit board, that is, the part of the circuit. A layer of lead-tin resist is pre-plated on the graphic part, and then the rest of the copper foil is chemically etched away, which is called metal etching.
The etching method is a method of removing the copper foil other than the conductive circuit with an etching solution, and the engraving method is a method of removing the copper foil other than the conductive circuit with an engraving machine. The former is a chemical method, which is more common, and the latter is a physical method. The circuit board etching method is a chemical etching method, which uses concentrated sulfuric acid to etch the circuit board made of unnecessary copper clad. The engraving method uses a physical method, using a special engraving machine, and the cutter head engraves the copper clad laminate to form a circuit trace.
Six Factors Affecting Side Erosion
Types of etching solution
Different chemical components of different etching solutions have different etching rates and different 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 nitric acid-based etching systems can achieve almost no undercutting, and the sidewalls of etched lines are nearly vertical.
Soaking and bubbling etching will cause larger side etching, splash and spray etching will cause smaller side etching, especially spray etching has the best effect.
Density of etching solution
If the density of the alkaline etching solution is too low, the side erosion will be aggravated. It is beneficial to use an etching solution with a high copper concentration to reduce the side erosion.
Slow etching rate will cause severe side erosion, and the improvement of etching quality has a lot to do with 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 etching, and the etched graphics are clear and tidy.
The pH value of the etching solution
When the pH value of the alkaline etching solution is high, the side erosion will increase. In order to reduce the side erosion, the general pH value should be controlled below 8.5.
Copper foil thickness
For the etching of thin wires with minimal undercut, 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, the shorter the time in the etching solution, and the smaller the amount of side etching.