The manufacturing of PCB board faces different methods to make required products and operations from the board. Of that method is surface finish. The copper layer existing on the board gets oxides after engaging with environmental moisture and air that causes a decrement in the soldering process of copper. If the board has a surface finish then layers of copper get protection from oxidation and provide good soldering and electrical operations.
Different types of surface finishes are used for board protection based on project demands ENEPIG is also a type of board finish. ENEPIG stands for Electroless Nickel Electroless Palladium Immersion Gold. It comes with lot of advantages so it is preferred for different applications
WHAT IS ENEPIG?
ENEPIG is metallic plating of the board that was an older technique but for some years, it got popularity since it is less costly than other types of gold plating. The prices of palladium are lowered than gold so the use of palladium plating on board in place of pure gold PCB finishes process can be less expensive so which makes ENEPIG famous for electronic plating.
The nickname o ENEPIG is Universal Surface Finish due to its features to be deposited on any type of PCBA. These finishes are normally used for soldering support and bonding of gold and aluminum wires. With these features, ENEPIG finish also increases the shelf life of the board where it is applied for more than one year
How ENEPIG applied
There are four layers of metal are deposited in this finish. Which are copper, nickel, palladium, and gold. The process of ENEIG applications is explained here
Copper Activation
In this step copper which is the protection layer is selectively activated which defines the deposition configuration in the electroless nickel plating phase. This step is performed through the use of a displacement reaction that creates a copper layer-like catalytic surface.
Electroless Nickel
Nickel operates as barrier layers protecting copper from interaction with other metallic materials used in this finish especially gold. The layer is deposited on the catalytic copper surface through the use of an oxidation-reduction reaction. The resultant layer has a thickness between 3 and 5 microns
Electroless Palladium
The palladium layer is the main difference between ENEPIG and ENEG finishes which is operating as a barrier layer. Palladium protects the nickel layer from corrosion and diffusion in the gold layer. It also operates as an anti-oxidation and anti-corrosion layer. Similar to nickel this layer is applied through the use of an electroless reaction that used a chemical oxidation-reduction reaction to result in a nickel surface to make a reaction with palladium and make a thin layer. The palladium layer has a thickness of 0.05 to 0.1 microns
Immersion Gold
The gold layer is the last layer that completes the ENEPIG surface finish process, resulting in less contact resistance, protection from friction, and resistance against oxidation. The gold layer also works as a protection for palladium solderability. According to its name immersion gold plating, completely immerses the covered board through the use of displacement reaction while the palladium layer at the board’s surface is dissolved and electrons are released from it reducing gold atoms around it. Ions of gold connected to the board surface replace palladium ions and cause a comparatively thin external layer having a thickness of 0.03 to 0.05 microns which is less than any other type of solution having gold plating
Features of ENEPIG
- The main features of ENEPIG are explained here
- it can withstand numerous lead-free soldering cycles
- it is a good example of gold wire bondability
- It has very less chance of grain boundary corrosion of nickel surface through immersion of gold
- The prices for ENEPIG material and process are lower than the ENIG
- The deposition of different layers of nickel, palladium, and gold protects copper layers existing underneath them
- ENEPIG is the best option for mixed technology and RF applications where a direct gold surface finish causes assembly problems.
ENEPIG Advantages
- Some benefits of ENEPIG are explained below
Cost Effective
- As there are some extra expenses involved for the processing stages of ENEPIG but its overall process is less than the electrolytic nickel finish. It is primarily since decreased material expenses related to ENEPG than ENEG. ENEG finish needs nickel deposition of gold on the basis of deposition technique whereas ENEPIG finish deposits a very thin layer of both palladium and gold. The decrement in costs of palladium makes it a less expensive solution than gold
High Durable Finish
- ENEPIG comes with numerous layers that make it corrosion corrosion-resistant finish that is due to the anticorrosive features of gold and palladium. This corrosion resistance avoids the existence of black nickel the term used for nickel corrosion on the outer surface of the nickel. The surface of ENEPIG also is smooth and poreless which means corrosive components have a very minor chance of depositing on the board which makes ENEPIG durable
The high value of Wire Bond Pull Strengths
- Aluminum and gold metal wire have great compatibility with ENEPIG plating. After the application of numerous testing techniques ENEPIG finish protects aluminum and gold wire from a high level of stress applied for a longer duration. it defines the great bondability features for these two metallic wires
High-Quality Solderability
- The soldering joint strength of ENEPIG finish is high-quality. This finis has compatibility with differnt types of alloy during reflow soldering in the absence of lead and can withstand numerous reflow soldering cycles without any damage. This compatibility is required since the palladium finish completely dissolved after soldering. It results in an oxide-free nickel surface which is a fine option for a stable nickel-to-tin configuration for soldering
Less Contact Resistance
- Less value of contact resistance is compulsory to avoid overheating for the board, with energy loss and poor grounding technique. ENEPIG finish has this less resistance since the controlled deposition of nickel, palladium, and gold converts the electrical resistance of the finish to uniform
Protection Barriers
- Nickel and palladium layers in this finish work as barrier layers to protect the copper from getting affected by tin during soldering. These barrier helps to enhance the solderability. They also reduce the mixing process of copper with gold to affect the conductivity
ENEPIG Advantages over ENIG
ENEPIG finish can fulfill ultra-demanding projects with numerous packaging categories, through holes, BGA, SMT, wire bonding, etc ENEPIG is mostly preferred for applications where wire bonding is required since that has the feature of high wire bond pull strength like aluminum wire up to ten grams and gold wires about eight gram.
it is also the board finish has a thickness of about 0.05 to 0.15 um so its soldering and assembly process is easy and reliable. ENEPIG also has some similarities to ENIEG like linger shelf lie since has resistance from tarnish and durability
Some advantages of ENEPIG over ENIG are listed here
- ENEPIG has protection from Black pad there is no chance of grain boundary corrosion of nickel surface through immersion gold.
- It is the best solution for high-operation applications
- It puffed for high-density assemblies
- It is used in mixed packages projects then ENIG
- it comes with a flat surface which is the best option for soldering
- ENEPIG is Lead-free and has compatibility with RoHS
- It has a Longer shelf life of more than one year
- Since it has no corrosion risk after assembly so used or good for touch contacts
