A printed circuit board needs to have a surface finish or coating to protect the copper circuitry from oxidation. The surface finish is also used to provide a solderable surface when assembling to promote reliable solder joints for long-term performance.

HASL (leaded and lead free) has been the most commonly used PCB surface finish in the United States for many years. During the HASL process the printed circuit boards are completely submerged in a bath of molten solder. The excess solder is later removed by blowing hot air across the surfaces of the boards. HASL leaves uneven surfaces and is not suitable for fine pitch or if your boards require small via holes.

OSP is a low cost water-based organic surface finish used since the 70’s. A very thin layer can protect the copper surface from oxidation. OSP is environmentally friendly and provides a coplanar surface however, it has a relative low shelf live.

ENIG is considered the best lead-free finish for fine pitch (especially BGAs) because of its flat surface, good solderability and good shelf live (12 months). It consists of two layer metallic coatings. The nickel layer serves as a barrier to the copper and is the surface to which components are soldered. The gold layer protects the nickel during storage. ENIG can be brittle and is not recommended for applications where shock or strong vibrations.

CHARACTERISTIC/APPLICATIONS	HASL	OPS	ENIG
Manufacturing costs	Low	Low	High
Environmental Hazard	Yes	No	No
Thermal Stress	Yes	No	No
Surface Finish Durability	Robust	Fragile	Robust
Surface Flatness	Poor	Excellent	Excellent
Reworkability	Yes/Difficult	Yes/Easy	No
Finished Hole Size Uniformity	Poor	Good	Good
Good for fine pitch	No	No	Yes
Solderability	Good	Good	Good
Ideal for HDI products	No	No	Yes
Shelf Life	Long	Short	Long
Sensitive to Handling	No	Yes	Yes
Good for PTH	No	No	Yes
Reliability	High	Medium	High
Risk of Corrosion	No	Yes	Yes
Solder Join Integrity	Excellent	Good	Good
Exposed Copper	No	No	Yes

Price, availability, shelf life, reliability and the assembly process are key factors when selecting a PCB surface finish. While each finish has its own advantages and disadvantages, in most cases, the process, product or environment will dictate the surface finish that is best suited for your application. For example, if your printed circuit boards do not need to be RoHS, Sn/Pb HASL may be your best option. It is low in cost and widely available. If your boards need to be RoHS and have fine pitch components including BGA’s we recommend ENIG or immersion silver.

 

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I.C.T is a manufacturer of SMT machines. It mainly provides customers with SMT production lines including SMT Stencil Printers,  Pick and place machines, Reflow Oven, AOI Machine, Wave Soldering Machine and PCB Handling Machine etc. I.C.T has more than 25 researches on SMT and DIP technology,  for the world Customers provide SMT total solutions. There are successful cases of SMT technical team in Asia, Europe, America, Africa, and Australia.

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