prototype pcb fabrication

How to choose between immersion gold and immersion nickel-palladium gold?

In PCB manufacturing, the copper foil on the circuit board is susceptible to oxidation, which can seriously reduce the soldering quality. Through surface treatment, the copper foil can be prevented from oxidation, thereby ensuring excellent solderability and corresponding electrical performance. As a surface treatment method, ENIG (immersion gold) and ENEPIG (immersion nickel palladium gold) can not only meet the technical requirements of the PCB market, but also can do lead-free soldering, with great development potential.

In order to overcome the main weakness of ENIG, black nickel, ENEPIG came into being as an upgraded version of ENIG. By adding a palladium layer between electroplated nickel and immersion gold, the attack of immersion gold solution on the nickel layer is isolated, and its thickness is usually in the range of 0.05μm to 0.1μm. The palladium layer plays a role in preventing the immersion gold technology from corroding the nickel layer. Therefore, ENEPIG can overcome the black nickel defect of ENIG.

In addition, ENEPIG has highly reliable wire bonding capability, excellent multiple reflow soldering capability, and contains switch contact surfaces, enabling it to simultaneously meet the stringent requirements of high-density and multi-surface packaging PCBs. Based on these advantages, ENEPIG is also known as a universal surface treatment.

Advantages of ENIG and ENEPIG

Advantages of ENIG:

• Simple process mechanism

• Flat surface

• Good oxidation resistance

• Excellent electrical properties

• High temperature resistance

• Good thermal diffusion

• Long shelf life

• No skin effect

• Suitable for untreated contact surfaces

• Lead-free

Advantages of ENEPIG:

• Excellent multiple reflow cycles

• Able to ensure good soldering performance

• Highly reliable bonding capability

• Surface as a critical contact surface

• High compatibility with Sn-Ag-Cu solder

• Suitable for a variety of packages, especially for PCBs with a variety of package types

• No black nickel phenomenon

ENEPIG technology is developed based on ENIG technology, and its performance has been greatly improved by adding a palladium layer. The reasons are as follows:

a. The palladium layer has a dense film structure that completely covers the nickel layer. The phosphorus content in the palladium layer is lower than the normal content in the nickel layer, so the conditions for the generation of black nickel are avoided and the possibility of black nickel disappears.

b. The melting point of palladium is 1,554°C, which is higher than the melting point of gold (1,063°C). Therefore, the melting speed of palladium at high temperature is relatively slow, and there is enough time to generate a resistance layer to protect the nickel layer.

c. Palladium is harder than gold, which improves the reliability of welding, wire welding (bonding) ability and friction resistance.

d. Tin-palladium alloy has the strongest anti-corrosion ability, which can prevent gradual corrosion caused by galvanic corrosion, thereby extending the service life.

e. The use of palladium can reduce the thickness of the gold layer, reducing the cost by 60% compared with ENIG.

Disadvantages of ENIG and ENEPIG

In addition to the advantages mentioned above, ENIG and ENEPIG also have some disadvantages.

Disadvantages of ENIG:

• Affected by the electroplating conditions and the overall process control

• Affected by the thickness of the electroplated nickel and metal

• Electroplating is affected by the size of the metal area in the electroplating tank

• Relatively low wettability

• Prone to black nickel phenomenon

Disadvantages of ENEPIG:

• Reduced welding performance due to the thick palladium layer

• Slower wetting speed

• Higher cost

Based on the advantages and disadvantages of ENIG and ENEPIG, when reliability is prioritized, ENEPIG will naturally be chosen as a better solution. However, ENEPIG does cost more.