: Provides ideal low contact resistance for keypads, switches, and interface joints. Core Plating Requirements and Thickness Metrics
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.
Using an obsolete revision risks non-compliance with OEM customer requirements. ipc4556 pdf
Assemblies undergoing multiple reflow cycles must maintain integrity. The outlines thermal shock and aging tests that the plated copper must survive without cracking or oxidation failure.
Protects the palladium from contaminants and ensures high-quality solderability and wire bondability. : Provides ideal low contact resistance for keypads,
Recommends X-ray Fluorescence (XRF) spectroscopy as the primary non-destructive method to measure the thin palladium and gold layers accurately.
| Feature | IPC-4552 (ENIG) | IPC-4556 (ENEPIG) | | :--- | :--- | :--- | | | Electroless Nickel / Immersion Gold (2 layers) | EN + EP + IG (3 layers) | | Wire Bonding | Primarily Aluminum wire bonding | Gold, Aluminum, and Copper wire bonding | | Key Weakness | Susceptible to "black pad" corrosion after soldering | Palladium layer prevents hyper-corrosion, offering higher reliability | | Gold Thickness | Minimum of 0.05 µm (with a maximum added in rev. A) | Tighter range: 0.03 - 0.07 µm | ipc4556 pdf
Heavy copper layers are heavy. This creates unique issues during the lamination process (pressing layers together with epoxy/prepreg). The standard outlines the peel strength requirements to ensure the heavy copper tracks do not lift off the substrate under thermal stress.