label: PCB surface treatment,PCB proofing,printed-circuit board
Surface of the board there are many types of treatment, PCB proofing personnel should be selected according to the board's performance and needs, the following simple analysis of PCB worry drawback under various surface treatments, for reference!
1. HASL hot air leveling (HAL we often say)
HASL PCB common early treatment. Now divided HASL and HASL.
Spray tin advantages:
- > Longer storage time
- > After the PCB is completed, the copper surface is completely wetting the (completely covered before soldering tin)
- > Suitable for lead-free soldering
- > Process maturity
- > Low cost
- > Suitable for visual inspection and electrical testing
HAL weakness:
- > Not suitable for wire binding; surface roughness due to problems in the SMT also has limitations; unsuitable for contact switch designs.
- > When HAL copper will dissolve, and the board is subjected to a high temperature.
- > Particularly thick or thin plate, HAL has limitations, inconvenient production operations.
2.OSP (organic protection film)
OSP advantages:
- > Process is simple, the surface is very smooth, suitable for lead-free soldering and SMT.
- > Easy to rework, to facilitate the production operation, suitable for horizontal operations.
- > Suitable for a variety of treatment coexist on the board (eg: OSP + ENIG)
- > Low cost, environment -friendly.
OSP weaknesses:
- > Reflow limit on the number (multiple weld thickness, the film would be destroyed, no problems substantially two times)
- > Not suitable for crimping technology, wire binding.
- > Visual inspection and electrical testing inconvenient.
- > N2 gas needs protection when SMT.
-> SMT rework unsuitable.
- > Storage conditions demanding.
3 Chemical Bank
Chemical Bank is a better surface treatment processes.
Chemical silver advantages:
- > Simple process for lead-free soldering, SMT.
- > Surface is very smooth
- > Suitable for very fine line.
- > Low cost.
Chemical silver weakness:
- > Storage conditions demanding, easily contaminated .
- > Welding strength prone to problems (micro- hole problem) .
- > Prone to electromigration phenomenon as well as copper and solder mask appears galvanic corrosion phenomenon bite.
- > Electrical measurement is also an issue
4 Chemical tin:
Tin is the most copper-tin chemical substitution reactions.
Chemical tin advantages:
- > Suitable level of production.
- > Suitable for fine line processing, suitable for lead-free soldering, especially for crimp technology.
- > Very good flatness, suitable for SMT.
Weaknesses:
- > Good storage conditions require, it is best not more than six months, in order to control the tin whisker growth.
- > Not suitable for touch switch design
- > The production process of the solder mask process requires relatively high, otherwise it will lead solder mask off.
- > When multiple welding, the best protection of N2 gas.
- > Electrical measurement also an issue.
5 . Chemical nickel-gold (ENIG)
Nickel Gold is an application of a relatively large surface treatment process, remember: nickel layer is a nickel -phosphorus alloy layer, based on phosphorus content into high phosphorous nickel and nickel- phosphorus, applications are not the same, the difference is not covered here.
Nickel Gold benefits:
- > Suitable for lead-free soldering.
- > Surface is very smooth, suitable for SMT.
- > Through holes can also be a nickel gold.
- > Longer storage time, storage conditions are not harsh.
- > Suitable for electrical testing.
- > Suitable switch contact design.
- > Suitable for aluminum wire binding, suitable for thick, strong resistance to environmental attack.
6 nickel plating
Nickel plating is divided into "hard money" and "soft gold", hard gold (example: gold -cobalt alloy) Common (contact connector design), soft gold is pure gold on the finger. Nickel plating in IC substrate (such as PBGA) on the application of more, mainly for gold and copper binding, but contains IC substrate plating suitable binding Goldfinger region needs to do additional conductive wire out to plating.
Nickel plating advantages:
- > Longer storage time > 12 months.
- > Suitable for contact switch design and gold thread binding.
- > Suitable for electrical testing
Weaknesses:
- > Higher cost, relatively thick gold.
- > Design requires additional electroplating line conductive finger.
- > Because gold has a thickness of not, used in the welding may result due to thick gold solder embrittlement impact strength.
- > Plating surface uniformity issues.
- > No nickel gold plated wrap wire side.
- > Not suitable for aluminum wire binding.
7 nickel- palladium (ENEPIG)
Nickel Palladium is now beginning to start in PCB field, before more on semiconductor applications. Suitable for gold, aluminum binding.
Advantages :
- > In the IC carrier board application, suitable for binding gold, aluminum binding. 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.
- > For a variety of surface treatment processes and the presence of the board.
Weaknesses:
- > Process complexity. Difficult to control.
- > In the field of application of PCB short history.
Source://www.seekic.com
