PCB surface finishes and shelf life

Views: 57 Author: Site Editor Publish Time: 2018-07-10 Origin: Site Inquire

A surface finish can be either organic or metallic in nature. Comparing both types and all available options can quickly demonstrate the relative benefits or drawbacks. Typically, the decisive factors when it comes to selecting the most suitable finish is the end application, the assembly process and the design of the PCB itself. Below you can find a brief summary of the most common finishes, however for further or more detailed information, please Viasion and we will be more than happy to answer any of your questions.

HASL - Tin/Lead hot air solder level Typical thickness 1 - 40um. Shelf life:12 months
	Excellent solderability Inexpensive / Low cost Allows large processing window Long industry experience / well known finish Multiple thermal excursions
	Difference in thickness / topography between large and small pads Not suited for < 20mil pitch SMD & BGA Bridging on fine pitch Not ideal for HDI products

LF HASL – Lead Free hot air solder level Typical thickness 1 - 40um. Shelf life: 12 months
	Excellent solderability Relatively inexpensive Allows large processing window Multiple thermal excursions
	Difference in thickness / topography between large and small pads - but to a lesser degree than SnPb High processing temperature - 260-270 degrees C Not suited for < 20mil pitch SMD & BGA Bridging on fine pitch Not ideal for HDI products

ENIG - Immersion gold / Electroless Nickel Immersion Gold Typical thickness 3 - 6um Nickel / 0.05 - 0.125um Gold. Shelf life: 12 months
	Immersion finish = excellent flatness Good for fine pitch / BGA / smaller components Tried and tested process Wire bondable
	Expensive finish Black pad concerns on BGA Can be aggressive to soldermask - larger soldermask dam preferred Avoid soldermask defined BGA's Should not plug holes on one side only

Immersion Sn - Immersion Tin Typical thickness ≥ 1.0µm. Shelf life: 6 months
	Immersion finish = excellent flatness Good for fine pitch / BGA / smaller components Mid range cost for lead free finish Press fit suitable finish Good solderability
	Very sensitive to handling - gloves must be used Tin whisker concerns Aggressive to soldermask - soldermask dam shall be ≥ 5 mil Baking prior to use can have a negative effect Not recommended to use peelable masks Should not plug holes on one side only

Immersion Ag - Immersion Silver Typical thickness 0.12 - 0.40um. Shelf life: 6 months
	Immersion finish = excellent flatness Good for fine pitch / BGA / smaller components Mid range cost for lead free finish Can be reworked
	Very sensitive to handling / tarnishing / cosmetic concerns - gloves must be used Special packaging required - if packaged opened and not all boards used, it must be resealed quickly. Short operating window between assembly stages Not recommended to use peelable masks Should not plug holes from one side only Reduced supply chain options to support this finish

OSP (Organic Solderability Preservative) Typical thickness 0.20-0.65µm. Shelf life: 6 months
	Excellent flatness Good for fine pitch / BGA / smaller components Inexpensive / Low cost Can be reworked Clean, environmentally friendly process
	Very sensitive to handling - gloves must be used and scratches avoided Short operating window between assembly stages Limited thermal cycles so not preferred for multiple soldering processes (>2/3) Limited shelf life - not ideal for specific freight modes and long stock holding Very difficult to inspect Cleaning misprinted solderpaste can have a negative effect on the OSP coating Baking prior to use can have a negative effect

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PCB surface finishes and shelf life

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