Electroless Nickel Immersion Gold

Principle of Electroless Nickel Immersion Gold

ENIG stands for electroless nickel immersion gold. It refers to an ENIG layer formed by chemical deposition on a bare copper surface to be soldered to maintain good solderability during the storage and assembly processes. ENIG layers are formed without additional electricity and only with the reductant in a high temperature bath solution. The constant deposition of nickel phosphorus alloy on activated metal surfaces to be plated can form ENIG surfaces. While the nickel layer is being dissolved to release two electrons after the nickel surface is placed in the immersion gold bath solution, the gold layer immediately acquires these electrons from the nickel surface which are then deposited thereon until the gold layer covers the whole nickel surface. As surface treatment for PCBs, ENIG has always been used in high-density electronic products.

Advantages of ENIG surface treatment:

  • Smooth surface
  • Long storage time
  • Bondable
  • Good electric testability
  • Supports cooling
  • Low contact impedance

Full ENIG process

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Brief introduction to the ENIG process and equipment 

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Pre-treatment (Sandblaster)
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Break-away Taping Machine
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ENIG Process Line
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Post Treatment

Process description

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ENIG reaction process chart

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Ni/P grains increase with the nickel plating time (crystal growth chart)

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Comparison chart of normal and abnormal nickel surfaces

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Comparison chart of normal and abnormal nickel surfaces : bad surface SEM analysis

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The effect of different copper surface treatment approaches on Ni/P grain morphology (sand blasting better than scrubbing)

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The effect of different copper surface treatment approaches on Ni/P grain morphology x 5000 times

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Using sand blasting for pre-treatment can reduce the boundary effect of crystallization

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