Spectroscopic Technique
Excitation of atoms by a primary electron beam triggers the emission of secondary electrons with energy levels characteristic of the source element. Auger electron spectroscopy identifies the chemical composition of the top few nanometers of a metallic surface. This method detects light elements and provides high spatial resolution for inspecting individual circuit board pads.
It relies on a non-radiative transition where an outer shell electron fills a vacancy and ejects a second electron. The secondary emission escapes only from the immediate surface, making the technique ideal for detecting thin films of contaminants that prevent proper wetting.
Elemental Identification
Energy peaks in the resulting spectrum correspond to specific electronic transitions within the sampled atoms. Oxygen and carbon levels on a solderable finish indicate the presence of organic residues or oxidation. Peak shifts reveal the oxidation state of the metal, distinguishing between pure nickel and nickel oxides.
Quantitative Mapping
Scanning the beam across a sample produces a lateral distribution map of the surface contaminants. This spatial data reveals whether a defect is localized to a single grain or distributed across the entire landing area. Integration of the signal intensity against a known reference allows for the calculation of atomic percentages at the interface.
Surface cleanliness directly determines the reliability of subsequent wire bonding or soldering steps.
