The palladium layer acts as a shield, completely neutralizing the risk of aggressive immersion gold chemistries attacking the nickel layer.
IPC-4556 is the industry standard titled
Boards finished to IPC-4556 specifications easily maintain their solderability for over 12 months in standard storage conditions, significantly outperforming OSP (Organic Solderability Preservatives) and Immersion Silver. Quality Control and Measurement Methods ipc4556 pdf
The IPC-4556 PDF details the precise measurement ranges for these layers. For example, it typically specifies nickel thickness at 3.0 to 5.0 microns, palladium at 0.05 to 0.15 microns (with a target of 0.10 microns often recommended for wire bonding), and gold at 0.03 to 0.05 microns.
Supporting gold, aluminum, and copper wire bonding on a single surface. The palladium layer acts as a shield, completely
This combination makes ENEPIG exceptionally versatile, suitable for soldering, gold/aluminum/copper wire bonding, membrane contacts, and even low/zero insertion force (LIF/ZIF) edge connectors.
Excellent wetting for SAC305 and other lead-free solders. For example, it typically specifies nickel thickness at 3
The standard specifies the requirements for Electroless Nickel/Electroless Palladium/Immersion Gold (ENEPIG) plating as a surface finish for printed circuit boards (PCBs) . Known as the "universal finish," ENEPIG is unique for its ability to support multiple assembly processes on a single board, including soldering, gold wire bonding, aluminum wire bonding, and contact applications. Key Thickness Requirements
Boards built to IPC-4556 specifications easily maintain their solderability for over 12 months in standard storage conditions.
IPC-4556 stands as the authoritative industry standard for ENEPIG surface finish on printed circuit boards. Whether you are specifying finishes for high‑frequency communications equipment, medical devices, automotive electronics, or aerospace applications, compliance with this standard ensures reliable, consistent, and durable PCB performance. The recent Revision A (2025) update demonstrates that IPC continues to refine and improve this essential document, keeping pace with evolving industry needs.