In the acid etching process of PCB manufacturing, the following process parameters need to be controlled with emphasis:
Etching solution concentration: The concentration of copper chloride is generally controlled at 180-220g/L. If the concentration is too low, it will lead to slow etching speed and incomplete copper foil etching. If the concentration is too high, it may cause excessive etching and increase costs at the same time. The concentration of hydrochloric acid is usually between 50 and 80g/ L. Its function is to adjust the pH value and enhance the etching capacity. A low concentration will reduce the activity of the etching solution and slow down the speed, while a high concentration will corrode the equipment.
Temperature: The appropriate etching temperature is generally between 45 and 55 degrees Celsius. A low temperature will slow down the etching reaction and reduce efficiency, while a high temperature will cause the etching solution to evaporate quickly and the reaction to be overly intense, making it difficult to control the accuracy.
Etching speed: It is usually controlled at 1-3 mil/min (1mil = 0.0254mm), and should be adjusted according to factors such as the thickness of the board and the copper foil. A speed that is too fast may lead to uneven etching, while a speed that is too slow will affect production efficiency.
Spray pressure: Generally maintained at 0.8-1.5kg/cm². If the pressure is too low, the etching solution will not be able to fully contact the copper foil, resulting in poor etching effect. If the pressure is too high, it may damage the already etched circuit or cause the etching solution to splash.
REDOX potential (ORP) : The etching rate is optimal when ORP is above 500, while above 580, it has little effect on the etching rate.
Specific gravity: When the specific gravity is less than 1.3, the etching rate increases with the increase of specific gravity. When the specific gravity is greater than 1.3, the etching rate decreases with the increase of specific gravity and is generally controlled at 1.300±0.03.
Acid equivalent: When the acid equivalent is 0-3N, the increase in the etching rate is proportional to the amount of hydrochloric acid. When the acid equivalent is 3-5N, the growth rate slows down. Increasing the acid equivalent can increase the etching rate, but it will also increase side etching. If side etching is to be controlled, the acid equivalent should not be too high.
Spraying pressure range: The optimal range is 1-3 kg/cm², and the upper pressure is usually about 0.5kg/cm² greater than the lower pressure.
