In Printed Circuit Boards (PCBs), the plating process is usually the final step. It is the process that gives the board its desired metal parts such as the copper pads and traces. The two most commonly used methods for PCB plating are electroless and electrolytic. In this blog post, we will explore both methods and compare them to help you better understand the differences between them.
Electroless Plating
As the name implies, electroless plating is a non-electrolytic process where immersion of the PCB into a solution results in the adsorption of metal ions which subsequently reduce to metal on the PCB surface. The immersion solution contains various chemical reducing agents that initiate the deposition process. Electroless plating is a relatively simple process that does not require any external power source. It is commonly used on through-holes, vias, and the surface of PCBs.
Electroless plating is known to be a more uniform and controllable process compared to electrolytic plating. This ultra-thin layer is ideal for very fine-pitched PCBs where the distance between the copper pads is small. The nickel and gold thickness is 2-6 μm and 0.05-2.5 μm, respectively. The electroless plating process takes around 30-60 minutes.
Electrolytic Plating
Electrolytic plating is an electrochemical process that uses a direct current (DC) to achieve the deposition of metal onto the PCB. The DC power source is used to create a circuit between the PCB acting as the cathode and a metal anode. The anode dissolves to provide the metal ions to be deposited on the PCB. This process deposits copper, tin or as a cheaper option, tin-lead onto the sites you wish to plate of the PCB using external power as a catalyst.
The deposition rate for electrolytic plating is much higher than that of electroless plating because of the current requirement. Electrolytic copper plating has a thickness of approximately 18-50 μm, while electrolytic gold plating thickness is usually in the range of 0.05-0.2 μm.
Comparing Electroless Plating and Electrolytic Plating
Both electroless and electrolytic plating have their strengths and weaknesses:
- Thickness consistency: Electroless plating produces more uniform and precise layers, which is more ideal for dense and high-resolution PCBs.
- Cost and time: Electrolytic plating is a relatively quicker method, the deposit rate is higher, and it is usually more affordable compared to electroless plating.
- Flatness: Electrolytic is denser due to a higher metal content, which means that it is not as flat as the electroless coating.
When it comes to choosing between these two methods, it is essential to consider the PCB's requirements, the project's scope and budget, and whether the coating will be used inside or outside.
References
- Wang, B. PCB Manufacturing Technology (Second Edition). Beijing: Posts & Telecom Press, 2006.
- Alcobe, X., Marin, E., & Sunol, J. Ultra-Fine Line Technology – Applications and Process Issues. In Proceedings of the CAST 2003, 2003.