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PCB Surface Finish Options

Not all circuit board surface finishes are alike. In order for a PCB engineer to specify which surface finish is right for the application, you need to look deeply into what the PCB will be exposed to during its lifetime.

Something as small as the amount of hand soldering or potential field repairs will play a big role in your choice of the best surface finish for your printed circuit board. For additional information, we also have a technical article on the advantages and disadvantages of surface finishes that will help with the selection for your PCB design.

Below are some of the detailed parameters of the most common surface finishes used in the PCB industry.

	Tin Lead HASL	ENIG	Ni & Hard Au	OSP	Immersion Silver	Immersion Tin
	Lead Free HASL	ENEPIG	Ni & Soft Au	OSP	ImAg	Immersion Tin
Design Attribute
Hole Compensation	Require 0.002 - 0.003 in.	STD	0.001 in. / Design Dependent	STD	STD	STD
Minimum Cleared Hole Size	max 6:1 aspect ratio *	No Limitation	No Limitation	No Limitation	No Limitation	No Limitation
Via Caps (post surface finish)	UV / Thermal	UV / Thermal	UV / Thermal	UV only	UV	UV only
Electrical Contact Use	Fair	Good for Low Wear Applications	Hard Au: Excellent Soft Au: Not Recommended	Not Recommended	Good for Low Wear Applications	Good for Low Wear Applications
SMOBC	Only	SMOBC = Yes Pre sm = design dependent	Yes if Tie bar	Only	Only	Only
Exposed Copper	None	None	Trace Edges (if not tie bar)	Un-assembled features after assembly	None	None
Manufacturing Process
Process Automation	Conveyorized or Vertical	Vertical only	Vertical	Conveyorized	Conveyorized or Vertical	Conveyorized or Vertical
Environmental & Process Hazards	High (Lead & Thermal)	Medium	Medium	Low	Low	High (Thiourea)
Quality Concerns	QFP Shorting / uBGA / Flatness	Skip/Extraneous Plate	Resist Lifting Plating Distribution	Handling	Handling	SM Attack / Handling
Gold Contacts	Tie bar ok Other: Design dependent	Low volume / Tie Bar	Thin Hard Au solderable Thick Hard Au for contact Thick Soft Au for Au wire bonding	No Limitation	Design Dependent (masking consideration)	Tie bar ok Other: Design Dependent
Finished PCB Rework Ability	Design Dependent	ENIG: Limited to Ni & Au brush ENEPIG: Unknown	Limited to Nickel & Gold brush	Easy	Limited	Medium
Equipment Maintenance	Intensive	Typical Vertical Process	Typical Vertical Process	Low	Low	Low
Thickness Measurement	XRF on Product	XRF on Product	XRF on Product	Spectrophotometer on Test Coupon	XRF on Product	XRF on Product
Manufacturability	Tin-Lead: 2 Lead-Free: 3	ENIG: 4 ENEPIG: 5	3	1	1	3
Assembly Considerations
Thickness Deposit	50 to 1500 uin IMC layer and planarity consideration	ENIG:2 to 6 uin Au / 150 to 250 uin Ni ENEPIG wide range (being defined by IPC committee)	Hard Au for solderability 5 to 15 uin Hard Au for contacts 30 to 50 uin Soft Au for wire bonding 40+ uinover a minimum of 150 uin of Ni	6 to 24 micro-inch chemistry dependent	6 to 18 uin	30 to 40 uinch minimum
Features Spacing	Less than 20 mils QFP = Limited	No limitation for SMOBC Preferably > 4 mils prior to SM	Line width & space and aspect ratio limitation	No Limitation	No Limitation	No Limitation
Solder Paste Misprint	Normal Wipe Down	Normal Wipe Down	Normal Wipe Down	Reduces Hold Times between Reflows	Supplier guidelines (cleaner restrictions)	Normal Wipe Down
Lead Free Assembly Compatible	Tin-lead: No Lead Free: Yes	Yes	Yes	Yes The newer generations	Yes	Limited to the number of reflow cycle
Other Considerations
Intermetallic Layer	Tin Copper	ENIG: Tin-Nickel ENEPIG: Tin- Palladium	Tin-Nickel	Tin Copper	Tin Copper	Tin Copper
Solder Joint Strength	Good for Tin-lead Limited data for lead free	ENIG: Good (Large BGA Issues)	Good	Excellent	Excellent	Good
Surface Finish Durability	Tin-lead: Good Lead Free: Unknown	Very Good	Very Good	Handling considerations	Handling and storage conditions	Good
Various	Thermal shock (preheat and solder bath) Lead Free: pre baking	ENIG: Ni layer for RF applications ENEPIG: Good for Au wire bonding	Nickel Layer for RF application	Holding time between assembly cycles	Storage, exposure to sulfur and halides	>Limited reflow cycle capability >Good for back plane applications >Intermetallic layer

* Equipment dependent

For more information on surfaces finishes, see our blog post titled Why Is PB Free HASL A Hassle.

Not Sure What Surface Finish Is Your Best Option?

Make informed decisions for your PCB surface finish after consulting our engineering experts to help you choose wisely and optimize longevity.

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