What is ENIG?

 Electro less Nickel/Immersion Gold (ENIG) is a double-layer metallic surface finish that is composed of a very thin layer of gold applied over a layer of nickel. A nickel layer is first plated onto the PCB copper pads using an electroless process, a controlled chemical reaction. Then a gold layer is applied on top of the nickel layer using immersion methods to cover the pads and traces.

Typically, an ENIG surface finish is only applied after a solder mask layer is applied; this is due to cost increases if all copper surfaces are plated with gold. After applying a solder mask layer, the layer of gold will be applied only to what is left exposed, reducing the total area plated with gold. The top layer of gold protects the nickel during the storage period, thus providing an excellent shelf life. This finish also provides a very flat surface, which is ideal for mounting parts such as Surface Mount Devices (SMDs) and Ball Grid Arrays (BGAs). ENIG is a finish preferred by many contract PCB assemblers due to the high electrical conductivity of gold.

As a result of the many advantages listed above, ENIG has become the most highly-used finish in the PCB industry since the growth and implementation of the RoHS regulation. Unfortunately, such great advantages cannot come without drawbacks, and for ENIG, the biggest drawback is it’s complex and sensitive application procedure. If this procedure is not properly controlled, quality issues such as "Black Pad" may occur. Black Pad is a buildup of phosphorous between the gold and nickel layers, which may result in fractured surfaces and faulty connections.


Go to the PCB knowledge Page
Go to the PCB design resources page
Back to the technology data