What are the surface treatment methods of PCB?
Surface Technology
Those with lead include: lead spray tin (HASL)
Lead-free ones include: lead-free tin spray, OSP, ENIG, ENEPIG, immersion silver
Applications, advantages and disadvantages of surface treatment methods
HASL
HASL is the main applied surface treatment technology, but from the perspective of new processes and lead-free requirements, it is not the best choice.
Advantages: low cost.
Disadvantages: 1. The HASL treated pad is uneven; 2. Lead has a negative impact on the environment.
OSP
Prevent copper from oxidizing before welding and protect the solderability of PCB pads from damage. The two OSP currently in use, Benzotriazoles and Imidazoles, both adhere well to bare copper surfaces.
Advantages: OSP does not have lead contamination problems.
Disadvantages: 1.OSP is transparent and colorless, making inspection difficult. It is difficult to tell whether the PCB has been coated with OSP; 2.OSP itself is insulated and non-conductive. It will affect electrical testing; 3.The OSP surface cannot come into contact with acidic substances, otherwise the OSP will volatilize.
ENIG
Plate Ni/Au on the copper surface. During soldering, the Au in the outer layer will quickly melt into the solder, and the solder and Ni form Ni/Sn intermetallic compounds. The purpose of plating gold on the outside is to prevent Ni from oxidation or passivation during storage, so The gold plating layer must be dense enough and not too thin.
Advantages: 1. The surface of PCB treated by ENIG is very smooth; 2.ENIG has good weldability.
Disadvantages: Complex, ENIG-treated PCB surface is prone to produce Black pad during the welding process, which will embrittle the solder joints and affect reliability.
ENEPIG
Compared with ENIG, ENEPIG has an extra layer of palladium between nickel and gold. Palladium can prevent corrosion caused by substitution reactions and is fully prepared for immersion gold.
Advantages: Widely used, it can replace nickel immersion gold. During the welding process, both palladium and gold will melt into the molten solder, thereby forming a nickel/tin intermetallic compound.
Disadvantages: Palladium is very expensive and the process requirements are strict.
Immersion silver
Through the immersion silver process, the copper surface is sealed by silver, which can extend the life. The surface of immersion silver is very flat and has good solderability.
Advantages: The immersion silver soldering surface has good solderability
Disadvantages: In a humid environment, silver will cause electron migration under the action of voltage
Dip tin
There are two reasons for using this process. One is that the surface of the immersed tin is very flat and has good coplanarity. The second reason is that dip tin is lead-free.
Advantages: The surface of dip tin is very flat and lead-free.
Disadvantages: Short life, especially when stored in high temperature and high humidity environments, the Cu/Sn intermetallic compound will continue to grow until it loses weldability.
How to choose surface treatment methods for different boards?
SMT: Can be selected according to customer requirements, no special restrictions;
Cards with gold fingers: selective gold plating;
Keyboard: Use immersion gold or gold plating process.
Understand the advantages, disadvantages and scope of use of surface treatment methods in various types of PCB, and you can choose the most appropriate method when choosing to achieve the best performance of PCB.
