pcb assembly

PCB surface treatment technology refers to form a layer that it is different from the mechanical, physical and chemical properties of the substrate on PCB components and electrical joints. The aim is to ensure good solderability or electrical properties of PCB. Because copper tends to exist in the form of oxides in air, the solderability and electrical properties of PCB are seriously affected, so the surface treatment of printed circuit board is needed.

The current common surface treatment methods are as follows:

1.HASL
The process of coating molten Tin lead solder on the Surface of PCB and heating compressed Air for leveling (blowing).It can form a coating that it is not only resistant to copper oxidation but also able to provide good solderability. The copper tin metal compound is at the solder and the copper bonding point. The thickness of the solder is about 1 ~ 2 mil.

2.OSP
A layer of organic membrane is grown chemically on the clean surface of bare copper. The film has the functions of anti-oxidation, anti-thermal shock, moisture-proof and so on. It is Used to protect the surface of copper from rust under normal conditions (oxidation or vulcanization, etc.); At the same time, it can be removed quickly by flux in the subsequent welding high temperature.

3.Immersion Gold
The electromechanical nickel-gold alloy coated with a thick layer on the copper surface ,and it can protect PCB. OSP is only used as an antirust barrier, it can be useful in the long time and achieve good electrical properties. In addition, it also has the tolerance to the environment that other surface treatment processes do not have it.The electromechanical nickel-gold alloy coated with a thick layer on the copper surface and can protect PCB. For a long time, OSP is a rust-proof barrier layer, it can be useful in the long time and achieve good electrical properties. In addition, it also has the tolerance to the environment that other surface treatment processes do not have it.

4.Immersion Silver
Between OSP and electroless nickel plating / gold leaching, the process is simple and rapid. it Expose in hot, wet and contaminated environment.And it still provides good electrical properties and maintains good solderability without luster. Because there is no nickel under the silver layer, the silver sink does not have all the good physical strength of electroless nickel plating / gold immersion;

5.Plated Gold
The electroplated nickel gold is electroplated on the surface of PCB with a layer of nickel and then a layer of gold. The main purpose of nickel plating is to prevent the diffusion between gold and copper. There are two types of electroplated nickel and gold: soft gold (pure gold, gold shows that it does not look bright) and hard gold plating (the surface is smooth and hard, wear-resistant, containing other elements such as cobalt, and the surface looks brighter). Soft gold is mainly used for gold wire in chip packaging; hard gold is mainly used for electrical interconnection in non-welded places (such as Gold finger).

6.Mixed surface treatment
PCB mixed surface treatment technology choose two or more than two surface treatment methods for surface treatment, common forms are: nickel deposition gold oxidation, electroplating nickel gold deposition nickel gold, electroplating nickel gold hot air leveling, The hot air leveled off the nickel and gold.

Of all surface treatments, hot air leveling (lead free / lead free) is the most common and cheapest treatment, but note the RoHS rules of the European Union.
RoHS: RoHS is a mandatory standard established by EU legislation. Its full name is《 the Directive on restricting the use of certain harmful components in Electronic and Electrical equipment》 (Restriction of Hazardous Substances). The standard has been put into practice since July 1, 2006. It is mainly used to standardize the materials and process standards of electronic and electrical products so as to make them more favorable to human health and environmental protection. The aim of the standard is to eliminate six substances, namely lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls and polybrominated diphenyl ethers in electrical and electronic products. The content of lead should not exceed 0.1%.