PCB Etching Acid vs Alkaline: A Battle of Chemicals
PCB etching is an indispensable process in the production of printed circuit boards. It involves removing the unwanted copper layer from the surface of the PCB, leaving only the traces of copper that form the circuitry. Two of the most common etching solutions are acids and alkaline solutions. In this post, we're going to compare the two and determine the pros and cons of each.
Acidic Solution
The most commonly used acidic solution for PCB etching is ferric chloride. It is a corrosive and hazardous chemical that needs careful handling, but it is effective and fast. Ferric chloride can dissolve copper at a rate of about 1.4 mm per minute. The etching time is typically around 5-10 minutes, depending on the thickness of the copper layer and the concentration of the solution. Acidic solutions are ideal for etching complicated and dense circuits.
Pros:
- Rapid and efficient etching.
- Suitable for dense and complicated circuits.
- Widely available in the market.
Cons:
- Corrosive and hazardous.
- Requires careful handling and disposal.
- Leaves a brownish residue that needs to be cleaned off.
Alkaline Solution
Sodium hydroxide, or caustic soda, is the most widely used alkaline solution for PCB etching. It is a less hazardous alternative to acidic solutions but less effective. Sodium hydroxide can dissolve copper at a rate of about 0.06 mm per minute, which is significantly slower than ferric chloride. The etching time with sodium hydroxide is typically around 30-40 minutes, which is much longer than acidic solutions. Alkaline solutions are best suited for etching simple and moderate-density circuits.
Pros:
- Less hazardous and easier to handle.
- Low cost.
- Suitable for simple and moderate-density circuits.
Cons:
- Slower etching rate.
- Longer etching time.
- Requires high temperatures to be effective.
Which one is better?
The choice of etching solution depends on the specifics of the PCB being produced. Ferric chloride is preferred for dense and complicated circuits because of its rapid and efficient etching. However, if the design is simple and the circuit density is low, sodium hydroxide is a better option because it's less hazardous and easier to handle.
It's essential to remember that both acids and alkaline solutions are hazardous chemicals that require careful handling and disposal. Before starting the etching process, always read and follow the safety instructions on the product labels.
References
- T. S. Chin, J. F. Wang, C. M. M. Ma, and W. M. Chou. "A Novel Etching Solution for Fast Etching of Copper in Printed Circuit Board Processing." Journal of The Electrochemical Society 152.6 (2005): G504-G508. [doi: 10.1149/1.1904882]
- W. Obermair, and M. Krutzler. "The Attack of Sodium-Persulfate and Sodium-Hydroxide on Copper Surfaces." Chemical Engineering & Technology 23.10 (2000): 909-12. [doi: 10.1002/1521-4125(200010)23:10<909::AID-CEAT909>3.0.CO;2-D]