At present the common PCB surface treatment methods have the following: PCB
1, Chemical immersion silver
Between OSP and electroless nickel/gold leaching, the process is simpler and quicker. Exposure to hot, humid and polluting environments can still provide good electrical properties and maintain good solderability, but will lose luster. Because there is no nickel underneath the silver layer, the silver deposit does not have the good physical strength of electroless nickel plating/immersion;
2, electroplating Nickel gold
On the PCB surface conductor plating on a layer of nickel before electroplating a layer of gold, nickel is mainly to prevent the spread between gold and copper. There are two types of nickel plating: Soft gold (pure gold, gold indicates no light) and plated hard gold (surface smooth and hard, wear-resistant, containing cobalt and other elements, the surface looks brighter). Soft gold is mainly used in the chip packaging when the gold wire, the hard gold is mainly used in the electrical interconnection (such as Goldfinger).
3, PCB mixed surface treatment technology
Choose two or more surface treatment methods for surface treatment, common forms are: immersion nickel gold + antioxidant, electroplating nickel gold + immersion nickel gold, electroplating nickel gold + hot air leveling, immersion nickel gold + hot air leveling.
All surface treatment forms of hot air leveling (lead-free/lead) are the most common and cheapest way to handle, but please note the EU RoHS regulations.
4. Hot air Leveling
On the PCB surface coated with molten tin-lead solder and heating compressed air leveling (Blow-flat) process, so that they form a layer of both copper oxidation and can provide a good solderability coating layer. The copper-tin metal compound is formed in the bonding place of solder and copper in the hot air, and its thickness is about 1~2mil.
5, Organic anti-oxidation (OSP)
On the surface of clean bare copper, a layer of organic skin film is grown by chemical method. This layer of film has antioxidant, heat shock, moisture resistance, to protect the copper surface in the normal environment no longer continue to rust (oxidation or vulcanization, etc.), but also in the subsequent welding high-temperature, it is easy to be helped by the flux quickly removed for welding;
6, chemical immersion nickel gold
The copper surface is coated with a thick, electrically good nickel-gold alloy and can protect the PCB for a long time. Unlike OSP, which is only used as antirust barrier layer, it can be used in the long-term use of PCB and achieve good electrical performance. It also has a tolerance to the environment that other surface treatment processes do not have.