WHAT IS ENEPIG?
ENEPIG PCB, is a type of metal plating PCB, Electroless Nickel - Electroless Palladium - Immersion Gold is a surface finish for Printed Circuit Boards.
Nicknamed the “universal surface finish” for its ability to be deposited on just about any PCB assembly, ENEPIG finishes are primarily used to support soldering and gold and aluminum wire bonding. On top of these functionalities, ENEPIG plating also extends the functional shelf life of a plated PCB well beyond a year.
HOW DOES ENEPIG WORK?
|Immersion Gold||1.2 microinches minimum|
|Electroless Palladium||2-12 microinches|
|Electroless Nickel||120-240 microinches|
Thicknesses of the four ENEPIG layers
ENEPIG involves four layers of metal deposited on a PCB surface. These are copper, nickel, palladium and gold. The process of creating an ENEPIG surface finish includes the following steps:
Copper Activation: In this step, the copper layer that needs protection is selectively activated, which determines the deposition pattern in the electroless nickel plating step. This process is accomplished using a displacement reaction, which makes the copper layer act as a catalytic surface.
Electroless Nickel: Nickel acts as a barrier layer, preventing copper from interacting with the other metals involved in this plating technology, particularly gold. The layer is deposited on the catalytic copper surface using an oxidation-reduction reaction. The result is a layer that is between 3.0 to 5.0 microns thick.
Electroless Palladium: The layer of palladium is what differentiates ENEPIG from ENEG surface finish technology, acting as another barrier layer. Palladium prevents the nickel layer from corroding and diffusing into the gold layer. It also acts as an anti-oxidation and anti-corrosion layer. Like nickel, this layer is deposited using an electroless reaction, which uses a chemical oxidation-reduction reaction to cause the nickel surface to react with palladium and form a thin layer. This palladium is deposited on a layer with a thickness of 0.05 to 0.1 microns, depending on the application.
Immersion Gold: Gold is the final layer added to ENEPIG surfaces, lending the benefits of low contact resistance, protection from friction and resistance to oxidation. Gold also preserves palladium’s solderability. As the name suggests, immersion gold plating services completely immerse the covered PCB, using a displacement reaction where palladium on the PCB dissolves and releases electrons that reduce the gold atoms surrounding it. The gold ions then attach to the surface of the PCB, replacing some palladium ions and resulting in a relatively thin outer layer, between 0.03 and 0.05 microns thick — substantially lower than any other solution.
Advantages of ENEPIG
The key advantages of ENEPIG, combining both excellent solder joint and gold wire bonding reliability can be summarized in the following points:
(1) "Black Nickel" free – no possibility of grain boundary corrosion of nickel surface by immersion gold;
(2) Palladium acts as an additional barrier layer to further reduce copper diffusion to surface, thus ensuring good solderability;
(3) Palladium completely dissolves into solder, without leaving an excessively high P% rich interface, exposing an oxide-free nickel surface allowing reliable formation of Ni/Sn intermetallic;
(4) Withstands multiple lead-free reflow soldering cycles;
(5) Demonstrates excellent gold wire bondability;
(6) Process costs substantially lower than ENIG and ENEG.
RayMing is 10 years ENEPIG PCB Manufacturer.
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