- Jun 30, 2017 -
Common PCB surface treatment process
Human environment for the continuous improvement of the living environment, the current PCB production process involved in the environmental problems is particularly prominent. The topic of lead and bromine is the hottest, lead-free and halogen-free will affect PCB development in many ways. Although the current point of view, PCB surface treatment process changes are not great, it seems still relatively distant things, but it should be noted: long-term slow changes will lead to a huge change. In the case of increasingly high environmental protection, PCB surface treatment process will certainly change the future.
The most basic purpose of surface treatment is to ensure good solderability or electrical properties. Since the natural copper in the air tends to exist in the form of oxides, it is unlikely that long-term retention of copper, so the need for other treatment of copper. Although in the subsequent assembly, you can use strong flux to remove most of the copper oxide, but the strong flux itself is not easy to remove, so the industry generally do not use strong flux.
There are many PCB surface treatment process, common is hot air leveling, organic coating, electroless nickel / leaching gold, silver and immersion tin of these five processes, the following will be introduced one by one.
1, hot air leveling (spray tin)
Hot air leveling, also known as hot air solder leveling (commonly known as spray tin), it is in the PCB surface coated with molten tin (lead) solder and heating compressed air by the whole (blowing) flat process, to form a layer of both copper oxidation, But also provide a good solderable coating. When the hot air is flattened, the solder and copper form a copper-tin intermetallic compound at the junction. PCB hot air leveling to sink in the molten solder; air knife in the solder before the liquid blowing liquid liquid; air knife to solder on the copper surface of the moon to minimize and prevent solder bridge.
2, organic solderability protective agent (OSP)
OSP is a process that meets the requirements of the RoHS Directive for printed circuit board (PCB) copper foil surface treatment. OSP is the abbreviation of Organic Solderability Preservatives, translated into organic solder film, also known as copper, English also known as Preflux. Simply put, OSP is in the clean bare copper surface, the chemical method to grow a layer of organic film. 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.); but in the subsequent high temperature welding, the protective film must be very Easy to be quickly removed by the flux, so that the exposed surface of the clean copper can be in a very short period of time with the molten solder immediately into a solid solder joints.
3, the whole board nickel plating
Plate nickel plating is the first surface of the PCB conductor coated with a layer of nickel and then coated with 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 surface does not look bright) and hard gold plating (surface smooth and hard, wear, containing cobalt and other elements, gold 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.
4, Shen Jin
Shen Jin is wrapped in a copper layer on the thick layer, the electrical good nickel alloy, which can protect the PCB for a long time; In addition it also has other surface treatment process does not have the tolerance of the environment. In addition, immersion gold can also prevent the dissolution of copper, which will benefit lead-free assembly.
5, Shen tin
Since all current solder is based on tin, the tin layer can match any type of solder. Shen tin process can form a flat copper-tin intermetallic compound, this feature makes Shen tin and hot air leveling with the same good solderability without hot air leveling headache flatness problem; Shen tin plate can not be stored for too long , Assembly must be based on the order of Shen tin.
6, Shen silver
The silver process is between organic coating and electroless nickel / immersion gold. The process is simple and fast. Even in exposed to hot, wet and polluted environments, silver is still able to maintain good solderability, but it will lose its luster The Shen silver does not have the good physical strength of electroless nickel plating / immersion gold because there is no nickel below the silver layer.
7, chemical nickel palladium gold
Chemical nickel palladium gold and gold compared to gold and gold is more than a layer of palladium, palladium can prevent the occurrence of displacement reaction caused by corrosion, for the preparation of immersion gold. Kim is closely covered with palladium, providing a good contact surface.
8, electroplating hard gold
In order to improve the wear resistance of the product, increase the number of plugging and electroplating hard gold. As the user requirements are getting higher and higher, the environmental requirements become more and more strict, more and more surface treatment process, in the end the choice of the development prospects, more versatile surface treatment process, now seems a bit confusing, confusing The PCB surface treatment process will go to the future, and now can not accurately predict. In any case, meeting user requirements and protecting the environment must be done first