A large number of quality problems related to the etched surface are concentrated in the etched part of the upper plate surface, and these problems come from the influence of colloidal structure produced by the etchant. It is very important to understand this, because colloidal agglomerates accumulate on the surface of copper. On the one hand, it will affect the jet force, on the other hand, it will block the fresh etching solution, so that the etching speed is reduced. Because of the formation and accumulation of colloidal crusts, the etching degree of the patterns on and below the substrate is different. The first substrate is easy to be completely etched or over etched because the accumulation has not been formed, and the etching speed is faster. The second substrate is easy to be etched or over etched because the accumulation has been formed, which slows down the etching speed.
Maintenance of etching equipment
The key factor to maintain the etching equipment is to ensure the high-definition cleanliness and no obstruction of the nozzle, so that the nozzle can spray smoothly. Blockage or slagging will cause pressure action during spraying and impact the plate surface. If the nozzle is not clean, it will cause uneven etching and waste the whole circuit board.
Obviously, the maintenance of the equipment is to replace the damaged and worn parts, because the nozzle also has the problem of wear, so the nozzle should be included in the replacement. In addition, the key problem is to keep the etching machine free of slagging, because too much slagging will affect the chemical balance of the etching solution. Similarly, if there is chemical imbalance in etching solution, slagging will be more serious. When a large amount of slagging suddenly appears in the etching solution, it is usually a signal that there is a problem in the balance of the solution. At this time, a strong hydrochloric acid should be used for proper cleaning or supplement of the solution.
Problems in etching process
Reduce the side corrosion and edge, improve the etching coefficient
Lateral erosion can produce protrusion. Generally, the longer the PCB is in the etching solution, the more serious the side corrosion is. Side corrosion will seriously affect the accuracy of printed wires, and it is impossible to make fine wires with serious side corrosion. When the side etch and bump edge decrease, the etching coefficient will increase. High etching coefficient means the ability to keep the thin wire, so that the etched wire can be close to the original size. Whether it is tin lead alloy, tin, tin nickel alloy or nickel electroplating etchant, excessive edge will cause wire short circuit. Because the protruding edge is easy to tear off, an electrical connection is formed between two points of the wire.
There are many factors that affect the lateral corrosion, which will be summarized below
1. Etching method s
Immersion and bubble etching can cause larger side corrosion, while splash and spray etching have smaller side corrosion, especially spray etching.
2. Types of etching solution
Different etching solutions have different chemical components, different etching rates and different etching coefficients.
For example, the etching coefficient of s-acid copper chloride solution is usually 3, while that of alkaline copper chloride solution is 4.
3. Etching rate:
Slow etching rate will cause serious side etching. The faster the etching speed is, the shorter the time the substrate stays in the etching, the smaller the amount of side etching, and the clearer and more orderly the etched pattern will be.
4. PH value of etching solution:
When the pH value of alkaline etching solution is higher, the side corrosion will increase. In order to reduce side corrosion, the pH value should be controlled below 8.5.
Density of etching solution:
The low density of alkaline etching solution will aggravate the side corrosion, and the etching solution with high copper concentration is very beneficial to reduce the side corrosion.
5) Copper foil thickness:
In order to achieve the minimum side corrosion of thin wire etching, it is best to use (ultra) thin copper foil. And the thinner the line width is, the thinner the copper foil should be. Because the thinner the copper foil, the shorter the time in the etching solution, and the smaller the side etching amount.