Printed circuit board surface finish

The bare copper on the PCB would oxidize and compromise the components soldering. As one of the last working steps in the PCB manufacturing, the bare copper on the PCB is coated with a surface finish.

The surface finish protects the underlying copper against oxidation and therefore increases storability. In addition, the surface finish is responsible for raising the wetting ability of the contact areas for soldering.

The selectable surface finishes vary in shelf life, typical application and price. Yet the surface finish is mostly determined by the following processing steps, the final product or the designated point of use of the final product.

Available surfaces

Surface	RoHS-compliant	Soldering	Bonding gold wire	Flex-/Rigid-Flex	PCI contacts	Thickness	Reflow Cycles
Surface	Hal SnPb	RoHS-compliant	Soldering	Bonding aluminium wire	Bonding gold wire	BGA	Flex-/Rigid-Flex	Pressfit	PCI contacts	Sliding contact	Thickness	>5µm	Shelf life	ca.12 months	Reflow Cycles	5**
Surface	HAL lead-free	RoHS-compliant	Soldering	Bonding aluminium wire	Bonding gold wire	BGA	Flex-/Rigid-Flex	Pressfit	PCI contacts	Sliding contact	Thickness	acc. to IPC-6012*	Shelf life	ca. 12 months	Reflow Cycles	5**
Surface	Chemical tin	RoHS-compliant	Soldering	Bonding aluminium wire	Bonding gold wire	BGA	Flex-/Rigid-Flex	Pressfit	PCI contacts	Sliding contact	Thickness	>1µm	Shelf life	ca. 6 months	Reflow Cycles	5**
Surface	Chemical silver	RoHS-compliant	Soldering	Bonding aluminium wire	Bonding gold wire	BGA	Flex-/Rigid-Flex	Pressfit	PCI contacts	Sliding contact	Thickness	0.2 - 0.3µm	Shelf life	ca. 6 months	Reflow Cycles	5**
Surface	Chemical gold ENIG	RoHS-compliant	Soldering	Bonding aluminium wire	Bonding gold wire	BGA	Flex-/Rigid-Flex	Pressfit	PCI contacts	Sliding contact	Thickness	3-6µm Ni 0.05-0.1µm Au	Shelf life	ca. 12 months	Reflow Cycles	5**
Surface	ENEPIG	RoHS-compliant	Soldering	Bonding aluminium wire	Bonding gold wire	BGA	Flex-/Rigid-Flex	Pressfit	PCI contacts	Sliding contact	Thickness	3-8µm Ni 0.05-0.15µm Pd 0.05-0.1µm Au	Shelf life	ca. 12 months	Reflow Cycles	-
Surface	Galvanic softgold	RoHS-compliant	Soldering	Bonding aluminium wire	Bonding gold wire	BGA	Flex-/Rigid-Flex	Pressfit	PCI contacts	Sliding contact	Thickness	4 - 6µm Ni >1µm Au	Shelf life	ca. 12 months	Reflow Cycles	-
Surface	Galvanic hardgold	RoHS-compliant	Soldering	Bonding aluminium wire	Bonding gold wire	BGA	Flex-/Rigid-Flex	Pressfit	PCI contacts	Sliding contact	Thickness	4 - 6µm Ni 0.8 - 2µm Au	Shelf life	ca. 12 months on request	Reflow Cycles	-

* IPC-6012: Fully covered and solderable | ** not reliable empirical values

HAL SnPb

HAL SnPb (lead-tin) is nowadays allowed only in certain technology fields such as medicine and aeronautics. HAL SnPb has been replaced by HAL lead-free. If the surface finish is specified only as HAL or HASL, typically the lead-free version is meant. HAL SnPb is suitable for standard SMD, but shows weaknesses in fine pitch applications. A chemical surface is preferable for finepitch (see also HAL vs. chemical gold).

Advantages:

Good solderability
Good reflow properties

Disadvantages:

Pads are non-planar
Not RoHS-compliant

HAL lead-free

HAL (Hot Air Leveling, also known as HASL = Hot Air Solder Leveling) lead-free is a well-proven method to apply tin as circuit board surface. Every assembler should be able to process circuit boards with HAL lead-free surface without any problem. HAL lead-free is suitable for standard SMD, but exhibits some weaknesses for finepitch applications, for which a chemical surface should be preferred (see also HAL vs. chemical gold). Due to popular demand, Multi-CB can offer HAL lead-free in pooling service (cheaper price).

Advantages:

Good solderability
Good reflow properties
Available in Pool-Service

Disadvantages:

Pads are non-planar

Chemical tin

The surface finish chemical tin (also known as immersion tin) is rarely requested anymore for manufacturing reasons. Due to the comparatively rapid oxidation of the copper, the shelf life is highly dependent on temperature and packaging. Fingerprints on the surface must be avoided.

Advantages:

Absolutely flat
Good for fine pitch
Good for SMD
Good for press-fit

Disadvantages:

Extra charge
Critical manufacturing process, handle with gloves
Faster oxidation, thus:
Limited storability
Better: use chemical gold

Chemical silver

Chemical silver (also known as immersion silver) is comparable to the surface finish chemical tin, with better properties concerning oxidation and contact applications. However, also chemical silver is a comparatively damageable surface finish and has therefore a low market share. Chemical silver is particularly suitable for high frequency applications, as the surface allows a low-loss HF transmission because of the skin effect.

Advantages:

Particularly suitable for high frequency applications (low-loss HF transmission because of the skin effect)
Absolutely flat
Good for fine pitch
Good for SMD
Good for press-fit
Better shelf life than chemical tin

Disadvantages:

Extra charge
Comparatively damageable surface finish, use gloves
Limited storability
Surface tarnishes over time and there can be creep corrosion
Solder mask defined pads should be avoided
Better: use chemical gold

Chemical gold (ENIG)

Chemical gold is also known as immersion gold or ENIG (Electroless Nickel Immersion Gold). Just as with chemical tin and chemical silver, chemical gold is an extremely flat circuit board surface, and has very good oxidation properties. It is perfectly suited for finepitch and bonding (aluminium wire) applications. Due to popular demand, Multi-CB can offer chemical gold in pooling service (cheaper price).

Advantages:

Absolutely flat
Very good for fine pitch
Very good for SMD
Very good wetting characteristics
Good for press-fit
Good storability
Available in Pool-Service

Disadvantages:

Possible extra charge

ENEPIG

ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold) is extremely planar and has very good oxidation properties. It is ideally suited for soldering applications and aluminum wire bonding / gold wire bonding.