A major advantage of following IPC-4556 is that it ensures the surface is compatible with diverse attachment technologies:
IPC-4556 specifies X-ray Fluorescence (XRF) as the primary method for verifying thickness. It mandates the use of Solid State Detectors (SSD) for better resolution on tri-level coatings and requires calibration against national standards. ipc4556 pdf
This critical update added a maximum gold thickness of 0.070 µm. This limit prevents "hyper-corrosion" of the nickel, which can occur if the gold plating process is too aggressive or prolonged. A major advantage of following IPC-4556 is that
ENEPIG was developed largely to solve the "black pad" corrosion issues sometimes found in ENIG (Electroless Nickel / Immersion Gold) finishes. The palladium layer acts as a buffer, preventing the immersion gold reaction from attacking the underlying nickel. This limit prevents "hyper-corrosion" of the nickel, which
High pull strengths for gold, aluminum, and even copper wire bonding.