PCB Final Finishes: ENEPIG

Electroless Nickel / Electroless Palladium / Immersion Gold (ENEPIG)

ENEPIG is formed by the deposition of electroless nickel, followed by electroless palladium, with an immersion gold flash. It is suitable for soldering, gold wire bonding, aluminum wire bonding, and contact resistance.

RoHS requirements, and increased focus on package reliability, have heightened interest in ENEPIG. ENEPIG performance is stellar in forming highly robust solder joints with lead-free SAC-type alloys.

In extended solder joint life testing (150°C for up to 1,000 hours), shear ball tests indicate no loss of solder joint strength. SEM studies and elemental analysis shows that the presence of palladium at the joint interface dramatically reduces inter-metallic (IMC) propagation, making ENEPIG the leading final finish process for packages that require soldering and wire bonding, with lead-free SAC type alloys.

The ENEPIG process is an excellent solution for IC package PCB substrates, particularly ceramic-based SiP products. Unlike electrolytic processes, ENEPIG carries no requirement for bussing lines, a factor which translates to additional flexibility in the design of circuits, and allows higher-density designs.

Finally, ENEPIG is immune to “black pad.” Palladium is plated onto the electroless nickel via chemical reduction, as opposed to a displacement reaction, so there is no opportunity for compromise of the electroless nickel layer.

The ENEPIG process is less expensive than electrolytic or electroless bondable gold. Savings can easily reach 80% of the total final finish cost when traditional electrolytic nickel gold processes are replaced with ENEPIG.

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Electroless Nickel

Nimuden® NPR-8  nickel-phos plating bath was developed for electronic and PCB applications, particularly those with fine line circuitry. NPR-8's higher phos content provides exceptional corrosion resistance; for OSP pretreatment, corrosion protection can be further increased with a higher %P. NPR-8 has adhesion characteristics superior to electroplated nickel. It is highly tolerant to dry film resist and soldermask, and is compatible with lead-free solders. The bath is highly stable; there is no risk of bridging or step plating.

Also available: NPR-4.

Electroless Palladium

Talon 3 deposits directly on copper, zincated aluminum or electroless nickel plated circuitry. The palladium surface is solderable as-plated, and gold or aluminum wire bondable when topcoated with immersion gold. The Talon bath has a low operating temperature, is highly stable, and tolerant to impurities (nitrate, copper, nickel.)

Also available: Talon 1, Talon 2.2.

Immersion Gold

Uyemura’s TWX-40 RAIG (Reduction Assisted Immersion Gold) uses immersion and autocatalytic modes of deposition to produce a thicker, lower porosity deposit that minimizes palladium’s exposure to the environment. The result is zero corrosion, exceptional deposit uniformity (independent of pad sizes and PCB surface potential) and compliance with IPC 4552 Rev. A. ENEPIG processors now have the option of depositing the heavier gold many designs call for – up to 8μin – in one step, while not risking the corrosion that is associated with heavier gold. The nature of the displacement reaction inherent in all competitor products is a primary cause of the corrosion that TWX-40 prevents with its unique "dual-reaction" process.

Also available: TAW-66, TAM-55.

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