Lead-Free Printed Circuit Board Surface Finishes

Printed Circuit Board finishes used to be simple consisting of either HASL (hot air solder leveling) or electrolytic nickel / gold. For years lead based finishes dominated the industry but technology and environmental concerns have altered the landscape for manufacturing printed circuit boards and more importantly the use of lead-free finishes used on circuit boards.

RoHS compliance , which took effect July 1, 2006, has established a new set of regulations requiring circuit board manufacturers to use lead-free finishes. There are a variety of lead-free finishes available today that meet RoHS compliance but it is important to understand the pros and cons of each finishing option and which to choose for your application.

Triangle Circuits has created a listing of lead-free printed circuit board finishes, providing both an explanation of the finish as well as a simple pros and cons comparison chart.

Please select from the list below to learn more about lead free circuit board finishes:

Organic Solderability Preservative – OSP
Immersion Silver
Electroless Nickel Immersion Gold – ENIG
Hard Gold
White Tin
Lead-Free Hot Air Solder Leveling – Lead-Free HASL
Lead Free Finishes - Comparison Chart

Organic Solderability Preservative (OSP's) lead-free finishes are available in different thicknesses, are inexpensive, provide good surface oxidation, coplanarity and are easy to apply. OSPs are limited in the number of heat cycles and some require a nitrogen environment at time of assembly. OSPs have a poor shelf life, degrade with high temperatures, have poor wettability and are not suited for wire bonding or as a contacting surface.

Immersion Silver lead-free finishes offer good wettability, low costs, and are re-workable. Tarnishing is handled with an anti-tarnishing ingredient applied during the silver bath step. Immersion Silver finishes have a good shelf life and must be packed using sulphur-free paper.

Electroless Nickel Immersion Gold - ENIG This finish is by far one of the best lead-free finishes available, but does require proficiency, knowledge and experience to properly fabricate printed circuit boards. Because this finish has special requirements Triangle Circuits has created a separate page for more details on ENIG.

Hard Gold This lead-free finish offers a variety of good properties including wettability, coplanarity, shelf-life as well as offering a good process window and process control. Unfortunately, Gold is a very expensive metal and is often too high priced to be used for some applications, in addition it can crack or break and cannot be reworked.

White Tin This finish is by far one of the best lead-free finishes available, but does require proficiency, knowledge and experience to properly fabricate printed circuit boards. Beeches this finish has special requirements Triangle Circuits has created a separate page for more details

Lead-Free Hot Air Solder Leveling This finish is by far one of the best lead-free finishes available, but does require proficiency, knowledge and experience to properly fabricate printed circuit boards. Because this finish has special requirements Triangle Circuits has created a separate page for more details

Lead-Free Printed Circuit Board Finishes Comparison Chart

Lead-Free Finish	Pros	Cons

Organic Solderability Preservative - OSP Lead-Free Finish	Good Coplanarity Good Surface Oxidation Reworkable Very Low Cost Good Process Window Good Process Control	Poor Shelf Life Degrades with High Temperature Reflow Cycles Flux Sensitivity Poor Wettability Very Poor Electrical Testability Poor Adhesion

Immersion Silver Lead-Free Finish	Good Wettability Good Shelf Life Good Coplanarity Good Reflow Cycles Re-workable Low Cost Good Process Control Good Electrical Testability	Must be packed using sulpher-free paper. Fair Process Window

Electroless Nickel Immersion Gold - ENIG Lead-Free Finish	Excellent Wettability Excellent Coplanarity Excellent Reflow Cycles Excellent Surface Oxidation Excellent Shelf-Life Good Adhesion Wire Bonding Good Electrical Testability	Moderate Cost Complex Process (Fabrication) Not Reworkable (Fabrication)

Hard Gold Lead-Free Finish	Good Wettability Good Coplanarity Good Reflow Cycles Good Surface Oxidation Good Shelf-Life Good Process Window Good Adhesion Good Electrical Testability	High Cost Not Re-Workable Brittle Au/SN Joints

White Tin Lead-Free Finish	Good Wettability Good Coplanarity Good Reflow Cycles Good Surface Oxidation Low Cost Good Process Control Good Adhesion Good Electrical Testability	Complex Process Fair Process Window Potential Tin Whiskers Hand Solder Difficulty

Lead Free Hot Air Solder Leveling HASL	Excellent Wettability Good Shelf-Life Excellent Reflow Cycles Excellent Surface Oxidation Low Cost Re-Workable Good Process Window Good Adhesion Excellent Solder Joints Good Electrical Testability	Process Control Poor Coplanarity Dark Solder Joints (Cosmetic)

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