Advantages and disadvantages of different surface treatment of PCB
There are many kinds of PCB surface treatment. PCB proofing personnel should choose according to the performance and demand of the board. The following is a brief analysis of the advantages and disadvantages of various PCB surface treatment for reference!
1. HASL hot air leveling (we often say tin spraying)
Tin spray is a common treatment in PCB early stage. Now it can be divided into lead-free tin spray and lead-free tin spray.
Advantages of tin spray:
-->Longer storage time
-->After PCB is finished, the copper surface is completely wetted (completely covered with tin before welding)
-->Suitable for lead-free welding
> low cost
-->Suitable for visual inspection and electrical measurement
Weakness of tin spray:
-->It is not suitable for wire binding; it is also limited in SMT due to surface flatness; it is not suitable for contact switch design.
-->When spraying tin, the copper dissolves and the plate undergoes a high temperature.
-->Special thick or thin plate, limited tin spraying, inconvenient production and operation.
2. OSP (organic protective film)
Advantages of OSP:
-->Simple process, very flat surface, suitable for lead-free welding and SMT.
-->Easy to rework, easy to operate, suitable for horizontal line operation.
-->The board is suitable for multiple processing (such as OSP + ENIG)
-->Low cost, environmentally friendly.
-->Limit of reflow welding times (multiple times of welding thickness, the film will be damaged, basically 2 times without problem)
-->Not suitable for crimping technology, wire binding.
-->It is not convenient for visual inspection and electrical measurement.
-->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.
Advantages of chemical silver:
-->Simple process, suitable for lead-free welding, SMT.
-->Very flat surface
-->Suitable for very fine lines.
Weaknesses of chemical silver:
-->The storage condition is high and easy to pollute.
-->The welding strength is prone to problems (micro void problem).
-->It is easy to have electromigration and javanni undercut with copper under solder mask.
-->Electrical measurement is also a problem
4. Chemical tin
Chemical tin is the most copper tin replacement reaction.
Advantages of chemical tin:
-->Suitable for horizontal production.
-->It is suitable for fine line treatment, lead-free welding, especially for crimping technology.
-->Very good flatness, suitable for SMT.
Weakness of chemical tin:
-->Good storage conditions are needed, preferably no more than 6 months, to control the growth of tin whiskers.
-->Not suitable for contact switch design
-->In the production process, the requirements for the solder mask process are relatively high, otherwise, the solder mask will fall off.
-->In case of multiple welding, N2 gas protection is preferred.
-->Electrical measurement is also a problem.
5. Chemical nickel gold (ENIG)
Nickel plating gold is a kind of surface treatment technology which is widely used. Remember: nickel layer is a nickel phosphorus alloy layer, which can be divided into high phosphorus nickel and medium phosphorus nickel according to the phosphorus content. The difference in application is not introduced here.
Advantages of nickel based gold:
-->Suitable for lead-free welding.
-->The surface is very flat and suitable for SMT.
-->Through hole can also be plated with nickel gold.
-->Longer storage time and less stringent storage conditions.
-->Suitable for electrical testing.
-->Suitable for switch contact design.
-->Suitable for aluminum wire binding, suitable for thick plate, strong resistance to environmental attack.
6. Nickel gold plating
Electroplated nickel gold is divided into "hard gold" and "soft gold". Hard gold (such as gold cobalt alloy) is often used on gold fingers (contact connection design). Soft gold is pure gold. Nickel plated gold is widely used in IC carrier plate (such as PBGA), which is mainly used for binding gold wire and copper wire, but it is suitable for electroplating on IC carrier plate. The binding area of gold finger needs additional conducting wire for electroplating.
Advantages of nickel gold plating:
-->Longer storage time > 12 months.
-->Suitable for contact switch design and gold wire binding.
-->Suitable for electrical testing
Weaknesses of nickel gold plating:
-->High cost, relatively thick gold.
-->Gold Plated fingers require additional design wire to conduct electricity.
-->Because the thickness of gold is not always, when it is used in welding, it may cause solder joint embrittlement and affect the strength due to too thick gold.
-->Plating surface uniformity.
-->Electroplated nickel gold does not cover the edge of the wire.
-->Not suitable for aluminum wire binding.
7 palladium nickel (ENEPIG)
Nickel and palladium are gradually applied in PCB field, and they were used more in semiconductor before. Suitable for binding of gold and aluminum wires.
Advantages of nickel and palladium:
-->It is suitable for binding of gold wire and aluminum wire. Suitable for lead-free welding.
-->Compared with ENIG, there is no nickel corrosion (black disk) problem; the cost is cheaper than ENIG and electronickel.
-->Long storage time.
-->It is suitable for various surface treatment processes and exists on the board.
Weaknesses of nickel and palladium:
-->The process is complex. Control is difficult.
-->It has a short history of application in PCB field.