Chinese
The finish consists in applying a layer of conductive material (tin, gold, silver, ...) on the pads and rings.
This layer improves the solderability of printed circuit and protects the copper parts against oxydation during storage.
Taili-PCB offers main finishes used in electronics:
. HAL (Hot Air Level)
. Chemical gold ENIG (Electroless Nickel Immersion Gold).
. Chemical gold ENIG + gold contacts (Hard Gold).
. Chemical gold ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold)
. Chemical Silver
. Chemical Tin
. OSP (Organic Solderability Preservative)
. Galavanic Hard GoldAL
HAL FINISH (Hot Air Leveling)
HAL : Hot Air Leveling - Leadfree - Rohs
The PCB is immersed in a bath of tin liquid . The tin covers copper parts not protected by soldermask. Tin is then "leveled" by a stream of hot air under pressure. This gives a tin thickness > = 5 micro
Benefits:
. Good solderability
. Good resistance to oxidation
. Cost
Disadvantages:
. Pads surface not planar
. Small SMD components fitting can be difficult (avoid HAL for very thin pads).
Shelf life:
. 6 to 12 months depending on conditions
CHEMICAL GOLD FINISH - ENIG
The circuit is successively immersed in a solution of acid +Nickel salts followed by a solution of gold. Nickel, first covering pads on a thickness of 3 microns can "block" the diffusion of gold in the copper layer.
Thickness of gold finish : 0.04 .. 0.08µm
Benefits:
. Very good solderability
. Better resistance to oxidation than chemical tin
. Good characteristic for reflow
. Well suited for fine pitch and SMD
. Best surface in most of cases
. Well suited for CMS and fine steps (BGA)
. Compatible with Wire Bonding
Disadvantages:
. Cost for volume orders
Shelf life:
. 6 to 12 months depending on conditions
CHEMICAL GOLD + PALLADIUM - ENEPIG
ENEPIG - Electroless Nickel Electroless Palladium Immersion Gold
Finish for PCB same as ENIG finish but with Electroless Palladium plating.
This type of surface plating combine both excellent solderability and gold wire bonding reliability. "Black Nickel" free - no possibility of grain boundary corrosion of nickel surface by immersion gold. This finish is recommended for gold wire bonding applications.
Thickness of Palladium layer: 0.05 um +/-0.02 um.
Benefits:
. Very good solderability
. Very good for alu-wire-bonding
. Very good for gold-wire-bonding
. Better resistance to oxydation between gold and copper than ENIG
. Good characteristic for reflow
. Best surface in most of cases
. Adapted to fine pitch and SMD
Disadventages:
. More expensive than ENIG finish
. No pooling possible
Shelf life:
. 6 to 12 months depending on conditions
CHEMICAL SILVER FINISH
This finish is obtained by chemical deposition - circuit immersed in a solution acid + silver salts. The silver covers parts of copper apparent by transfer of Cu to acid solution and silver ions to copper layer.
Thickness of silver obtained: > 0,2µm.
Benefits:
. Good solderability.
. Better resistance to oxidation than chemical tin.
. Good characteristic for reflow.
Disadventages:
. More expensive than HAL
. Short operating window between assembly stages
Shelf life:
. 3 to 6 months depending on conditions
CHEMICAL TIN FINISH
This finish is obtained by chemical deposition - circuit immersed in a solution acid + tin salts. The tin covers parts of copper apparent by transfer of Cu to acid solution and tin ions to copper layer. Thickness of tin obtained: > 0,8 µm (Typically : 1µm)
Benefits:
. Good solderability.
. Good characteristic for reflow.
. Well suited for fine pitch and SMD
. Low cost
Disadventages:
. More expensive than HAL.
. Fast oxydation
. Very short operating window between assembly stages
Shelf life:
. 3 to 6 months depending on conditions
OSP FINISH (Organic Solderability Preservative)
OSP is a protective layer applied to the pads to be welded. This protection prevents oxidation and / or deterioration of these pads during transport and storage. Does not involve any additional cost.
Is used directly on bare copper PADs. Replaces the finish.
OSP thickness obtained: 0.2 to 0.5 µm
Benefits:
. Prevent oxidation during storage and delivery
. No additional cost
Disadventages:
. Disapearring when solder
. Short operating window between assembly stages
. Fragile during manipulation
Shelf life:
. 3 months depending on conditions