There are many types of circuit board surface treatments. PCB proofers should choose according to the performance and needs of the board. The following is a brief analysis of the advantages and disadvantages of various PCB surface treatments for reference!

1. HASL hot air leveling (we often say spray tin)

Tin spraying was a common treatment in the early days of PCB. Now divided into lead spray tin and lead-free spray tin.　　

The advantages of tin spraying:　　

–>Longer storage time　　

–>After the PCB is completed, the copper surface is completely wetted (the tin is completely covered before soldering)　　

–>Suitable for lead-free soldering　　

–>Mature technology　　

–>Low cost　　

–>Suitable for visual inspection and electrical measurement 　　 Weaknesses of tin spraying:　　

–>Not suitable for wire binding; due to surface flatness, there are limitations on SMT; not suitable for contact switch design.　　

–>The copper will dissolve when spraying tin, and the board will withstand a high temperature.　　

–>Especially thick or thin board, spray tin has limitations, production and operation are not convenient.

2. OSP (Organic Protective Film)
Advantages of OSP:
　　–>The process is simple, and the surface is very flat, suitable for lead-free soldering and SMT.
　　–>Easy to rework, convenient production and operation, suitable for horizontal line operation.
　　–>The board is suitable for multiple processing coexistence (for example: OSP+ENIG)
　　–>Low cost and environmentally friendly.

Weaknesses of OSP:

　　–>The limit of the number of reflow soldering (the film will be damaged if the thickness of multiple soldering is thick, and there is basically no problem in the second time)
　　–>Not suitable for crimping technology, wire binding.
　　–>Visual inspection and electrical measurement are not convenient.
　　–>N2 gas protection is required for SMT.
　　–>SMT rework is not suitable.
　　–>High storage requirements.

3. Chemical silver
Chemical silver is a better surface treatment process.
　　The advantages of chemical silver:
　　–>Simple process, suitable for lead-free soldering, SMT.
　　–>The surface is very flat
　　–>Suitable for very fine lines.
　　–>Low cost.
Weaknesses of chemical silver:
　　–>The storage conditions are high, and it is easy to be contaminated.
　　–>Welding strength is prone to problems (microvoiding problems).
　　–>Electromigration is prone to appear as well as Javanni bite corrosion on the copper under the solder mask.
　　–>Electrical measurement is also a problem

4. Chemical tin
Chemical tin is the most copper-tin replacement reaction.
　　The advantages of chemical tin:
　　–>Suitable for horizontal production.
　　–>Suitable for fine line processing, suitable for lead-free soldering, especially suitable for crimping technology.
　　–>Very good flatness, suitable for SMT.

　　The weakness of chemical tin:
　　–>Good storage conditions are required, preferably not more than 6 months, to control the growth of tin whiskers.
　　–>Not suitable for contact switch design
　　–>The solder mask process requirements are relatively high in the production process, otherwise it will cause the solder mask to fall off.
　　–>N2 gas protection is best when welding multiple times.
　　–>Electrical measurement is also a problem.

5. Chemical nickel gold (ENIG)
Nickel gold is a relatively large surface treatment process. Remember: the nickel layer is a nickel-phosphorus alloy layer. According to the phosphorus content, it is divided into high-phosphorus nickel and medium-phosphorus nickel. The application is different, so the difference is not introduced here.
　　The advantages of nickel-gold:
　　–>Suitable for lead-free soldering.
　　–>The surface is very flat, suitable for SMT.
　　–>Through holes can also be coated with nickel and gold.
　　–>Long storage time, storage conditions are not harsh.
　　–>Suitable for electrical testing.
　　–>Suitable for switch contact design.
　　–>Suitable for aluminum wire binding, suitable for thick plates, and strong resistance to environmental attacks.

6. Electroplated nickel gold
Electroplated nickel gold is divided into “hard gold” and “soft gold”. Hard gold (such as gold-cobalt alloy) is commonly used on gold fingers (contact connection design), and soft gold is pure gold. Electroplating of nickel and gold is widely used on IC substrates (such as PBGA). It is mainly suitable for bonding gold and copper wires. However, the plating of the IC substrate is suitable. The bonded gold finger area needs to be electroplated with additional conductive wires.
　　The advantages of electroplating nickel gold:
　　–>Longer storage time>12 months.
　　–>Suitable for contact switch design and gold wire binding.
　　–>Suitable for electrical test

　　 Weaknesses of nickel-gold electroplating:
　　–>Higher cost, thicker gold.
　　–>Additional design lines are required for electroplating gold fingers to conduct electricity.
　　–>Because the thickness of gold is not constant, it may cause embrittlement of the solder joints and affect the strength when the gold is too thick.
　　–>The uniformity of the plating surface.
　　–>The electroplated nickel gold does not cover the edge of the wire.
　　–>Not suitable for aluminum wire binding.

7. Nickel Palladium (ENEPIG)
Nickel-palladium-gold is now gradually beginning to be applied in the PCB field, and it has been used more in semiconductors before. Suitable for bonding of gold and aluminum wires.
　　The advantages of nickel palladium gold:
　　–>Application on IC carrier board, suitable for gold wire bonding and aluminum wire bonding. Suitable for lead-free soldering.
　　–>Compared with ENIG, there is no nickel corrosion (black plate) problem; the cost is cheaper than ENIG and electric nickel gold.
　　–>Long storage time.
　　–>Suitable for a variety of surface treatment processes and stored on the board.

　　 Nickel Palladium Weaknesses:
　　–>The process is complicated. Difficult to control.
　　–>The application history in the PCB field is short.