Advantages and disadvantages of different PCB surface treatment

  There are many types of Surface treatment for PCB board production. Usually PCB engineer will consider according to the board's performance and needs. Following is some reference from the advantages and disadvantages PCB under various surface treatments.

1.     HASL/ HAL Hot Air Leveling surface treatment

HASL surface treatment is a common finishing. It is divided into HASL and Lead-free HASL.

Advantages:
-> Longer storage time
-> The copper surface is completely covered with tin after PCB completed (completely covered before soldering tin)
-> Suitable for lead-free soldering
-> Process maturity
-> Low cost
-> Suitable for visual inspection and electrical testing

Disadvantages:
-> Not suitable for wire binding; Due to problems of surface roughness , there is some limit in the SMT, unsuitable for contact switch designs
-> Copper will dissolve in the HASL process, and the PCB board suffers high temperature
-> With limit for some particularly thick or thin circuit board, it is inconvenient for production operations

　　2. OSP (Organic Solderability Preservative)

Advantages:
-> Process is simple; the surface is very smooth; suitable for lead-free soldering and SMT
-> Easy to rework; production operation is simple; suitable for horizontal operations
-> Suitable for a variety of treatment coexist on the board (eg. OSP + ENIG)
-> Low cost, environment-friendly

Disadvantages:
-> Reflow times limit (the film would be destroyed if it is multiple weld/soldering, usually no more than two times will be ok)
-> Not suitable for crimping technology, wire binding
-> Not inconvenient for visual inspection and electrical testing
-> N2 gas protection needed when SMT

-> Unsuitable for SMT rework
-> Good Storage conditions demand

  3.     Chemical Silver
Chemical Silver is good surface treatment processes.

Advantages:

-> Process is simple, suitable for lead-free soldering
-> Surface is very smooth
-> Suitable for fine line
-> Low cost
Disadvantages:

-> High requirement on storage conditions

-> Easy with problem in welding strength (micro-hole blank problem).
-> Prone to with electro migration as well as galvanic corrosion phenomenon bite under copper and solder mask
-> Electrical measurement is also an issue

4. Immersion Tin
Immersion tin is copper-tin chemical substitution reactions.

Advantages:
-> Suitable for line production
-> Suitable for fine line processing, suitable for lead-free soldering, especially for crimp technology
-> Good flatness, suitable for SMT

Disadvantages:
-> Good storage conditions required. The storage period is better no more than six months, avoid tin whisker grow
-> Not suitable for touch switch design
-> The production process of the solder mask process requires relatively high, otherwise it will lead to solder mask off
-> When multiple welding, it is better protected by N2 gas
-> Difficult with Electrical testing

　

　5. Chemical nickel-gold (ENIG)

Immersion Gold is a widely used surface finishing .Please note that the nickel layer is a nickel-phosphorus alloy layer. Based on phosphorus content, it is divided into high phosphorous nickel and nickel-phosphorus. Their applications are not the same. We won’t discuss about their difference here.

Advantages:
-> Suitable for lead-free soldering
-> Surface is smooth, suitable for SMT
-> Through holes also can be immersed Gold
-> Long storage time. Not strict storage conditions

-> Suitable for electrical testing
-> Suitable switch contact design
-> Suitable for aluminum wire binding and thick board; strong resistance to environmental attack　

Disadvantages:

->Cost high

->Black block

->Use cyanide and other hazardous chemicals

6. Plating Gold

Plating gold is divided into "hard gold" and "soft gold". Hard gold (for example gold-cobalt alloy) is common used in Gold finger (contact connector) design. Soft gold is pure gold. Gold plating is frequently used in IC substrate (such as PBGA).It suitable for gold bonding and copper bonding. But for COB contains IC plating, the Gold finger needs to do conductive wire out additionally for plating.

Advantages:
-> Long storage time> 12 months
-> Suitable for contact switch design and gold wire bonding.
-> Suitable for electrical testing

Disadvantages:

-> Higher cost due to relatively thick gold
-> Need to design additional conductive line for electroplating finger
-> Because of different gold thickness, it is possible cause embrittlement problem which may influence the strength
-> Problem of plating surface uniformity

-> No nickel gold plated wrap wire side
-> Not suitable for aluminum wire bonding.

　　

7. Nickel-Palladium (ENEPIG)

Nickel Palladium now start to be used in PCB field, which usually is used semiconductor applications before.

Advantages:

-> In the IC board application, suitable for binding gold, aluminum bonding, suitable for lead-free soldering.
-> Compared with ENIG, no corrosion of nickel (black plate) problem,costs cheaper than ENIG electroless nickel and gold.
-> Long storage time.
-> Suitable for a variety of surface treatment processes

Disadvantages :
-> Process complex, difficult to control.
-> PCB field application history is short