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

SurfacePCB RoHS-compliantRoHS-compliantPCB solderingSolderingPCB Bonding aluminium wireBonding aluminium wirePCB Bonding gold wireBonding gold wirePCB BGABGAPCB Flex-/Rigid-FlexFlex-/Rigid-FlexPCB PressfitPressfitPCB PCI contactsPCI contactsPCB sliding contactSliding contactPCB surface thicknessThicknessPCB shelf lifeShelf lifePCB Reflow CyclesReflow Cycles
SurfaceHal SnPbPCB RoHS-compliantRoHS-compliant PCB solderingSolderingcheckPCB Bonding aluminium wireBonding aluminium wire PCB Bonding gold wireBonding gold wire PCB BGABGA PCB Flex-/Rigid-FlexFlex-/Rigid-Flex PCB PressfitPressfit PCB PCI contactsPCI contacts PCB sliding contactSliding contact PCB surface thicknessThickness>5µmPCB shelf lifeShelf lifeca.12 monthsPCB Reflow CyclesReflow Cycles5**
SurfaceHAL lead-freePCB RoHS-compliantRoHS-compliantcheckPCB solderingSolderingcheckPCB Bonding aluminium wireBonding aluminium wire PCB Bonding gold wireBonding gold wire PCB BGABGA PCB Flex-/Rigid-FlexFlex-/Rigid-Flex PCB PressfitPressfit PCB PCI contactsPCI contacts PCB sliding contactSliding contact PCB surface thicknessThicknessacc. to IPC-6012*PCB shelf lifeShelf lifeca. 12 monthsPCB Reflow CyclesReflow Cycles5**
SurfaceChemical tinPCB RoHS-compliantRoHS-compliantcheckPCB solderingSolderingcheckPCB Bonding aluminium wireBonding aluminium wire PCB Bonding gold wireBonding gold wire PCB BGABGAcheckPCB Flex-/Rigid-FlexFlex-/Rigid-Flex PCB PressfitPressfitcheckPCB PCI contactsPCI contacts PCB sliding contactSliding contact PCB surface thicknessThickness>1µmPCB shelf lifeShelf lifeca. 6 monthsPCB Reflow CyclesReflow Cycles5**
SurfaceChemical silverPCB RoHS-compliantRoHS-compliantcheckPCB solderingSolderingcheckPCB Bonding aluminium wireBonding aluminium wirecheckPCB Bonding gold wireBonding gold wire PCB BGABGAcheckPCB Flex-/Rigid-FlexFlex-/Rigid-Flex PCB PressfitPressfitcheckPCB PCI contactsPCI contacts PCB sliding contactSliding contact PCB surface thicknessThickness0.2 - 0.3µmPCB shelf lifeShelf lifeca. 6 monthsPCB Reflow CyclesReflow Cycles5**
SurfaceChemical gold
ENIG
PCB RoHS-compliantRoHS-compliantcheckPCB solderingSolderingcheckPCB Bonding aluminium wireBonding aluminium wirecheckPCB Bonding gold wireBonding gold wire PCB BGABGAcheckPCB Flex-/Rigid-FlexFlex-/Rigid-FlexcheckPCB PressfitPressfitcheckPCB PCI contactsPCI contacts PCB sliding contactSliding contact PCB surface thicknessThickness3-6µm Ni
0.05-0.1µm Au
PCB shelf lifeShelf lifeca. 12 monthsPCB Reflow CyclesReflow Cycles5**
SurfaceENEPIGPCB RoHS-compliantRoHS-compliantcheckPCB solderingSolderingcheckPCB Bonding aluminium wireBonding aluminium wirecheckPCB Bonding gold wireBonding gold wirecheckPCB BGABGAcheckPCB Flex-/Rigid-FlexFlex-/Rigid-Flex PCB PressfitPressfitcheckPCB PCI contactsPCI contacts PCB sliding contactSliding contact PCB surface thicknessThickness3-8µm Ni
0.05-0.15µm Pd
0.05-0.1µm Au
PCB shelf lifeShelf lifeca. 12 monthsPCB Reflow CyclesReflow Cycles-
SurfaceGalvanic softgoldPCB RoHS-compliantRoHS-compliantcheckPCB solderingSolderingcheckPCB Bonding aluminium wireBonding aluminium wire PCB Bonding gold wireBonding gold wirecheckPCB BGABGA PCB Flex-/Rigid-FlexFlex-/Rigid-Flex PCB PressfitPressfit PCB PCI contactsPCI contacts PCB sliding contactSliding contact PCB surface thicknessThickness4 - 6µm Ni
>1µm Au
PCB shelf lifeShelf lifeca. 12 monthsPCB Reflow CyclesReflow Cycles-
SurfaceGalvanic hardgoldPCB RoHS-compliantRoHS-compliantcheckPCB solderingSoldering PCB Bonding aluminium wireBonding aluminium wire PCB Bonding gold wireBonding gold wire PCB BGABGA PCB Flex-/Rigid-FlexFlex-/Rigid-Flex PCB PressfitPressfit PCB PCI contactsPCI contactscheckPCB sliding contactSliding contactcheckPCB surface thicknessThickness4 - 6µm Ni
0.8 - 2µm Au
PCB shelf lifeShelf lifeca. 12 months
on request
PCB Reflow CyclesReflow Cycles-

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

PCB surface HAL SnPb

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:

PCB surface HAL leadfree

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
PCB surface chemical tin (immersion tin)

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
PCB surface chemical silver (immersion silver)

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
PCB surface chemical gold (ENIG)

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
PCB surface ENEPIG

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.

Advantages:

  • Absolutely flat
  • Very good for alu-wire-bonding
  • Very good for gold-wire-bonding
  • Very good for fine pitch, SMD
  • Very good wetting characteristics
  • Good storability

Disadvantages:

  • Extra charge