There are many types of surface treatment for printed circuit board(PCB), PCB proofing staff according to the board’s performance and needs to choose, the following simple analysis of the PCB surface treatment of various worries, for reference!

1. Hot air leveling (Known as HASL)

HASL is the most common used in PCB processing. Now HASL is divided into two kinds processing, spray tin with lead and spray tin with lead-free.

Advantage of HASL:
-> Longer storage time
-> When PCB is completed, the pads is completely wet (completely covered with tin before welding)
-> Suitable for lead-free soldering
-> Mature
-> Low cost
-> Can be in visual inspection and electrical measurement

Weakness of HASL:
-> not suitable for line binding; due to surface roughness problems, there are limitations in the SMT; Can not be used touch switch.
– When HASL, the copper will dissolve and the board is subjected to a high temperature.
-> particularly for thick or thin panel, HASL is limited, the production processing is not convenient.

2.OSP (organic protective film)

Advantages of OSP:
-> Simple process, the surface is very smooth, suitable for lead-free soldering and SMT.
-> easy to rework, easy to operate, suitable for horizontal production line.
-> One panel can have different surface finish (such as OSP + ENIG)
-> Low cost, environmental friendly.

Weaknesses of OSP:
-> Cannot take too many times in reflow soldering (After soldering times, the film will be destroyed, normally can be welded 2 times)
-> not suitable for crimping technology, line binding.
-> It is not convenient for visual inspection and electrical measurement.
-> Requiring N2 gas protection while SMT.
-> High requirement for Storage conditions.

3.Immersion silver

Immersion silver is a better surface treatment process.

Advantages of chemical silver:
-> Simple process, suitable for lead-free soldering, SMT.
-> The surface is very flat
-> Suitable for very fine traces.
-> Low cost.

Weaknesses of Immersion Sliver:
-> High requirement for Storage conditions. Easy to be polluted.
-> May have some welding strength problems (micro-hole problem).
-> prone to electromigration phenomena and the copper under solder mask will meet galvanic corrosion phenomenon.
-> Hard to electric test

4.Immersion Tin

Immersion Tin is the pronest to copper and tin replacement reaction.

Immersion Tin Advantages:
-> suitable for horizontal production line.
-> Suitable for fine trace processing, suitable for lead-free soldering, especially for crimping technology.
-> Very good flatness, suitable for SMT.

-> Requiring good storage conditions, had better not to storage for more than 6 months in order to control the tin whisker to grow.
-> Not suitable for contact switch.
-> High requirement for solder mask processing or solder mask will be off.
-> When multiple welding, We need N2 gas protection.
-> Hard to electric test.

5. Immersion Gold (ENIG)

ENIG is a widely-used surface treatment processing
nickel layer is nickel-phosphorus alloy layer, according to the phosphorus content is divided into high phosphorus nickel and phosphorus nickel. The application is not the same, here we do not introduce the difference.

Advantages of Nickel:
-> suitable for lead-free soldering.
-> The surface is very flat, suitable for SMT.
-> Through-hole can also be plated with nickel gold.
-> Storage for longer time, storage conditions are not harsh.
-> suitable for electric test.
-> suitable for contact switch.
-> suitable for aluminum binding, suitable for high thick panel, can hold more environmental attacks.

6. Hard Gold

Electroplating nickel gold is divided into “hard gold” and “soft gold”, hard gold (such as gold and cobalt alloy) commonly used in the gold finger (connection design), soft gold is pure gold. Hard gold is often used in the IC carrier board (such as PBGA), mainly for gold and copper wire binding. Gold finger area need to add additional conductive trace to plating.

Advantages of Hard Gold:
-> longer storage time> 12 months.
-> suitable for contact switch and gold wire binding.
-> suitable for electric test

Weaknesses of Hard Gold:
-> Higher cost, gold is thicker.
-> Electroplating gold finger will need an additional conductive trace.
-> Due to the thickness of the gold is not coherence, so hard gold is not always used in welding.
-> Plating surface uniformity problem.
-> plated nickel gold does not wrap the edge of the line.
-> not suitable for aluminum trace binding.

7. Nickel palladium (ENEPIG)

Nickel palladium is now beginning to be used in PCB, ENEPIG is used to be applicated in the semiconductor. Suitable for gold and aluminum trace binding.

-> Application in the IC carrier board, suitable for gold wire binding, aluminum binding. Suitable for lead-free soldering.
-> Compared with ENIG, there is no nickel corrosion (black plate) problem; cost is cheaper than ENIG and nickel.
-> long storage time.
-> Suitable for variety of surface treatment processes and on board.

-> Complex process. Hard to control.
-> ENEPIG is a new method and not mature enough.

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