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On complex PCBs, engineers often need different areas of the board to handle different bonding methods. ENEPIG handles all of the following on a single board: Lead-free (SAC305) reflow soldering Leaded (SnPb) soldering Gold wire bonding Aluminum wire bonding Conductive adhesive interfaces Exceptional Shelf Life
IPC-4556, updated to Revision A in 2025, defines the performance requirements for Electroless Nickel/Electroless Palladium/Immersion Gold (ENEPIG) PCB surface finishes. The standard establishes strict thickness ranges to ensure reliable soldering and wire bonding while mitigating corrosion, with specific focus on tightening control over palladium and gold layers to prevent "black pad". Purchase the full technical standard at IPC Official Store electronics.org
If you are currently evaluating surface finishes for a new project, I can help you find: Specific PCB fabricators that specialize in ENEPIG. ipc4556 pdf
| | Thickness | Role & Key Notes | | :-------- | :----------------------- | :----------------------------------------------------- | | Nickel | 3 to 6 µm | Primary diffusion barrier; ensures wire bonding. | | Palladium | No explicit standard value given in initial searches; see related standard IPC-4556A | Blocks nickel diffusion; prevents hyper corrosion. | | Gold | Max. 0.070 µm (specific for immersion gold) | Protects palladium; ensures solderability and bondability. |
The update introduces higher expectations for nickel corrosion resistance. On complex PCBs, engineers often need different areas
in). Critical for preventing nickel corrosion (Black Pad) and enabling wire bonding. Minimum 0.030 in) to a maximum of 0.070 in). Protects the palladium and ensures solder wettability.
The choice between these finishes depends heavily on the application: is a general-purpose finish for soldering; ENEPIG is the versatile choice for mixed assemblies requiring soldering and wire bonding; and Hard Gold is the mandatory choice for edge connectors designed for frequent mating cycles. Purchase the full technical standard at IPC Official
The document outlines visual inspection criteria, allowing for minor, non-functional cosmetic variations while restricting defects that affect reliability. IPC-4556A Revision: What's New?