ENIG refers to Electroless Nickel Immersion Gold, or called Immersion Gold, is now one of most-used PCB surface finishes. The gold color of ENIG makes it easy to be distinguished. Actually Electroplating Gold possesses a similar color, but rarely used currently.
What is the advantage of ENIG?
The advantages of ENIG,
- flat surface, good for small SMD devices,
- reworking availability (>3 times reflow),
- excellent electrical conductivity,
- anti-oxidation & anti-rust,
- good heat dissipation,
- higher surface thickness
The disadvantages of ENIG,
- soldering joints are not so strong
- expensive than HASL and OSP
- risk of "Black pad" or "Black Nickel"
What is Black Pad in ENIG?
In the permutation reaction of ENIG process, if the nickel surface get excessive oxidation reaction, the metal nickel might convert into nickel ions, while the larger gold atoms (radius 144 pm) irregularly deposit to form a coarse and loose arrangement, which means the gold layer might fail to completely cover the nickel layer, allowing the nickel layer to contact with the air, which will finally create nickel rust under the gold layer. This kind of nickel rust will cause soldering failure.
So that another surface finish process called ENEPIG was come up to solve this problem of "black pad", but the cost of ENEPIG is relatively expensive, now it is more suitable for HDI boards, CSP or BGA.
How to create ENIG surface finish?
- Pretreatment: Remove oxides from the copper surface while roughening to increase the adhesion of nickel and gold,
- Micro Etching: Produce the uniform and flat copper surface,
- Activation: A layer of palladium (Pd) will be applied to the copper surface as a catalyst for the deposition reaction, palladium ions are reduced to palladium metal adhered to the copper surface,
- Nickel Plating: Block the diffusion between copper and gold, create a soldering base,
- Immersion Gold: Prevent the oxidation of the nickel layer.
What is Electroplating Gold?
Immerse the circuit board in the electrolyte tank and apply current to form a nickel-gold plating on the copper surface of the circuit board. It possesses higher hardness, so also called hard gold.
ENIG is one of the most made surface finishes by PS Electronics, the services contain custom gold thickness, selective gold plating, etc. If any issues about ENIG, just contact us to get it through.