What are the PCB surface treatment processes?

In the PCB manufacturing process, if the copper surface of the PCB board is exposed to the air for an extended period, it can lead to oxidation, affecting subsequent processing stages. Therefore, it is common practice during PCB fabrication to apply surface treatment to prevent the direct exposure of the copper surface to the air. So, what exactly is surface treatment technology, and what are the commonly used surface treatment processes?

PCB surface treatment technology refers to the process of forming a coating on the bare copper surface of a PCB through chemical methods or electrolytic principles to meet the functional requirements of anti-oxidation and anti-corrosion. The common PCB surface treatment technologies include: tin spraying, gold plating, electroless nickel gold plating (ENIG), and Organic Solderability Preservatives (OSP). Let's delve into each of them:

Tin Spraying Process:

Tin spraying, also known as hot air leveling, is a process where tin is sprayed onto the PCB surface and then leveled using hot compressed air. There are two methods: vertical tin spraying and horizontal tin spraying. Generally, the horizontal method provides the best results. Tin materials are classified into leaded and lead-free, resulting in leaded tin spraying and lead-free tin spraying. Leaded tin has better solderability but does not comply with EU environmental standards, so lead-free tin spraying is more commonly used.

OSP Process:

OSP (Organic Solderability Preservative) is a process that involves the chemical formation of an organic film on the bare copper surface of a PCB to prevent oxidation and corrosion. The organic film formed through OSP not only protects the PCB but is also rapidly removed at high temperatures during soldering, facilitating the soldering process. OSP is relatively simple and cost-effective, making it the most widely used surface treatment among all.

Electroless Nickel Gold Plating (ENIG) Process:

ENIG is a process where a chemical nickel layer is deposited on the bare copper surface of a PCB, followed by the deposition of a thin gold layer. ENIG provides a smooth surface, high solderability, and protection against oxidation and rust. PCBs treated with ENIG exhibit enhanced aesthetics.

Gold Plating Process:

Gold plating, also known as electroplating, involves depositing a low-stress nickel layer of about 3μm~8μm on the copper surface of the PCB, followed by a thin gold layer of 0.01μm~0.05μm. The nickel layer prevents diffusion between the gold layer and the copper surface, while the gold layer protects the nickel layer from oxidation or corrosion. Gold plating is categorized into hard gold plating and soft gold plating, each suitable for different application scenarios.

These various surface treatment processes have their distinct characteristics and advantages. Processes such as OSP, electroless nickel gold plating (ENIG), and gold plating differ significantly in their principles and procedures. While the mentioned treatments are commonly used in PCB fabrication, there are also less commonly used surface treatment processes like silver plating and tin plating.