The standard defines precise thickness ranges (typically measured on a 1.5mm x 1.5mm pad) to ensure reliability and prevent defects like "black pad" (nickel corrosion). Thickness ( Thickness ( μinmu i n 3.0 – 6.0 118.1 – 236.2 Diffusion barrier, strength Electroless Palladium (Pd) 0.05 – 0.15 2.0 – 12.0 Barrier between Ni and Au Immersion Gold (Au) 0.03 – 0.07 1.2 – 2.8 Solderability/Corrosion resistance
High-power COB (Chip-on-Board) LEDs require thick copper for heat spreading. IPC-4556 defines copper thickness that doubles as a thermal diffuser. ipc4556 pdf
The original IPC-4556 was released in . As of 2025, the current active revision is IPC-4556A (with Amendment 1) . When searching for an "ipc4556 pdf," verify the revision letter on the cover page. The original IPC-4556 was released in
Understanding IPC-4556: The Industry Standard for ENEPIG Surface Finish ipc4556 pdf