SURFACE FINISHING

ENIG = Electroless Nickel – Immersion Gold

‘ENIG’ (Electroless Nickel, Immersion Gold) in which a Ni thickness normally 3-5μm layer of electroless nickel is given a thin gold ‘flash’ coating by immersion plating Au thickness 0,05-0,12 μm, an ion exchange process which coats the whole of the nickel surface. It means that ENIG is an electroless nickel layer capped with a thin layer of immersion gold.

ENIG is usually applied selectively on all Copper areas still free after soldermask printing (coated polyimide coverlayer or laminated yellow adhesive coverlayer).

Application of soldermask after ENIG plating processes is possible but not recommended for laminated yellow adhesive coverlayer or coated polyimide as coverlayer, because it reduces the adhesion during etching processes.

ENIG advantages:

  • Good corrosion protection,
  • multiple reflow soldering,
  • long shelf life,
  • aluminum wire bonding
  • press fit connections
  • contact surface

The Electroless Nickel layer as barrier

  • Electroless nickel underlayer is first deposited, to act as a barrier to copper diffusion
  • Work as corrosion protection for the copper layer and prevents the build-up of an intermetallic copper gold layer.
  • 7-10% Phosphorous is plated with the Nickel increasing the brittleness.
  • Nickel deposition is an electro chemical process, enabled by prior activation of the copper surface by Palladium for bonding of Gold and Aluminum wire application.
  • Typical Nickel thickness range from 3 to 5 μm

The immersion gold processes plate 0.05–0.12μm

  • Gold finishing does not oxidize; its excellent solderability and ensure by subsequent reflow solder process does not degrade with time for designed fineline printing will be satisfactory.
  • Gold finishing readily dissolves in molten solder has to be liquid long enough to form a true intermetallic bond to the base conductor and will be present in the reflowed solder joint.
  • Intermetallic gold-tin compounds formed cause joints to be brittle, and the gold film must therefore be thin (<<1μm) to minimize the amount of intermetallics.
  • The immersion gold protects the underlying nickel from oxidation/passivation over its intended life.
  • AuSn embrittlement only occurs when at least 3-5% of gold is present in the joint.

 

ENEPIG = Electroless Nickel -Palladium- Immersion Gold

…. coming soon

Electro plated Nickel-Gold (E(Ni) – E(Au))

…. coming soon

OSP (Organic Solderability Preservative )

…. coming soon

 

SURFACE FINISHING PROCESS ENIG ENEPIG ENi-EAu OSP
Thickness

Ni: 3-5μm

Au: 0.05–0.12μm

Ni: 3-7μm

Pd : 0.075-0.250μm

Au: 0.05–0.12μm

Ni: 3-7μm

Au: 0.5–2.5μm

 0.3-0.6
Temperature
Composition
Resistivity
Line/Space