PCB surface treatment technology refers to the process of artificially forming a surface layer with different mechanical, physical and chemical properties from the substrate on PCB components and electrical connection points. PCB surface treatment The purpose is to ensure the PCB good weldability or electrical performance. Since copper tends to exist in the form of oxide in the air, which seriously affects the solderability and electrical properties of PCB, PCB surface treatment is required.Common PCB surface treatment include the following:
1,PCB surface treatment hot wind leveling
The process of coating the surface of PCB with molten tin and lead solder and heating compressed air leveling (blowing) to form a coating layer that is both anti-copper oxidation and provides good weldability.PCB surface treatment Hot air usually solder and copper in the junction of the formation of copper tin compounds, the thickness of about 1 ~ 2mil;
2. PCB surface treatment Oxidation resistance (OSP)
A layer of organic skin film is grown on a clean bare copper surface chemically. This film has anti-oxidation, heat shock, moisture resistance, to protect the copper surface in normal environment no longer continue to rust (oxidation or vulcanization, etc.); At the same time must be in the follow-up welding high temperature, can be easily by the flux quickly cleared, for welding;
3.PCB surface treatment Chemical precipitation of nickel and gold
A thick layer of nickel-gold alloy with good electrical properties on the copper surface can protect the PCB for a long time. Unlike OSP, which is only used as a rust-proof barrier layer, it can be useful in the long-term use of PCB and achieve good electrical performance. In addition, it also has the environmental tolerance that other surface treatment processes do not have.
4. PCB surface treatment Chemical silver precipitation
Between OSP and electroless nickel/gold plating, the process is simple and fast. Exposure to heat, moisture and pollution will still provide good electrical properties and maintain good weldability, but will lose luster. Because there is no nickel under the silver layer, the precipitated silver does not have all the good physical strength of electroless nickel/gold plating;
5.PCB surface treatment Nickel and gold plating
The conductors of PCB are plated with nickel and then plated with gold. The main purpose of nickel plating is to prevent the diffusion of gold and copper. Currently there are two types of nickel gold plating: soft gold (pure gold, which indicates a dull surface) and hard gold (a smooth, hard surface containing cobalt and other elements, which gives a shiny surface). Soft gold is mainly used for chip packaging when gold wire; Hard gold is mainly used in non-soldering electrical interconnections (eg goldfinger).