Surface Specification
An international industry standard defines the acceptable thickness range for both the electroless nickel and the immersion gold layers on printed circuit board pads. Achieving the correct ipc 4552 enig thickness prevents solderability issues and protects the nickel layer from oxidation prior to assembly. Plating thickness of the gold layer must be sufficient to prevent nickel oxidation but thin enough to avoid causing gold embrittlement in the solder joint.
The standard specifies a nickel thickness between three and six micrometers, while the gold layer must sit between point zero five and point one five micrometers.
Measurement Protocol
Measurement of the plating thickness is executed using x-ray fluorescence instruments that are calibrated to known standards. Test operators scan specific control pads on the panel to confirm the deposit meets the specification. These scans must be performed on at least three pads of different sizes to ensure uniform deposition across the board.
Corrosion Protection
Insufficient nickel thickness leads to rapid diffusion of copper from the pad into the solder, which compromises the mechanical strength of the assembly. Conversely, if the gold layer is excessively thick, it increases the risk of the corrosive reactions that lead to brittle solder joints. Keeping the thickness within the defined range secures the long term electrical and mechanical performance of the board.
