- Jul 12, 2017 -
Several simple PCB surface treatment methods are summarized
Preface: PCB surface treatment technology refers to the PCB components and electrical connection point to form a layer with the matrix of the mechanical, physical and chemical properties of the surface of the different methods. The aim is to ensure good PCB solderability or electrical performance. As the copper in the air tend to exist in the form of oxides, seriously affect the PCB solderability and electrical properties, so the need for PCB surface treatment.
The current common surface treatment methods are the following:
1, hot air leveling
The surface of the PCB is coated with a molten tin-lead solder and is heated (compressed) by heating the compressed air to form a layer of coating that is resistant to both copper oxidation and good solderability. Hot air leveling when the solder and copper at the junction of the formation of copper and tin metal compounds, the thickness of about 1 ~ 2mil;
2, organic oxidation (OSP)
On a clean bare copper surface, grow a layer of organic film in a chemical way. This layer of film with anti-oxidation, heat shock, moisture resistance, to protect the copper surface in the normal environment is no longer continue to rust (oxidation or curing, etc.); at the same time must be in the subsequent high temperature welding, can easily be helped Flux is quickly removed for welding;
3, chemical sink nickel gold
In the copper surface wrapped in a thick layer, good electrical properties of nickel alloy and long-term protection of PCB. Unlike the OSP only as a rust barrier layer, which can be used in the PCB long-term use and to achieve good electrical performance. In addition it also has other surface treatment process does not have the patience of the environment;
4, chemical Shen silver
Between OSP and electroless nickel / dip gold, the process is simple and fast. Exposure to hot, wet and contaminated environments can still provide good electrical properties and maintain good solderability, but will lose luster. Because there is no nickel below the silver layer, so the silver does not have the chemical nickel plating / immersion gold all the good physical strength;
5, plating nickel gold
In the PCB surface conductor on the first layer of nickel after plating on a layer of gold, nickel is mainly to prevent the spread between gold and copper. There are two types of electroplating nickel: plating gold (gold, gold that does not seem bright) and hard gold plating (surface smooth hard, wear, containing cobalt and other elements, the surface looks more bright). Soft gold is mainly used for chip packaging when playing gold; hard gold is mainly used in non-welded electrical interconnection (such as gold finger).
6, PCB mixed surface treatment technology
Choose two or more surface treatment methods for surface treatment, the common forms are: Shen nickel + anti-oxidation, electroplating nickel gold + nickel nickel, gold plating + hot air leveling, Shen nickel + hot air leveling The