Diagnostic Utility
Microscopic analysis using co-axial electron and ion beams allows material engineers to examine the internal structure of printed circuit boards at the sub-nanometer scale. This dual-beam instrument, referred to as focused ion beam sem, exposes sub-surface features by sputtering material with gallium ions while generating high-resolution images with an electron beam. The technique reveals buried defects such as micro-voids and plating cracks without the distortion typical of mechanical cross-sectioning.
Precision positioning ensures that specific failure locations, such as a fractured copper microvia or a solder joint void, are targeted with sub-micron accuracy.
Cross Section
Target preparation begins with the deposition of a protective platinum or tungsten layer to shield the surface from damage during ion milling. This layer ensures that the subsequent milling step by the focused ion beam sem produces a clean, vertical wall for observation. The ion source gradually removes thin slices of the board material to expose the underlying structures.
Solder Assessment
Characterization of intermetallic compound layers at the solder pad junction represents a primary application of this method. Advanced imaging using focused ion beam sem distinguishes between copper-tin phases and nickel-tin phases with high chemical contrast. Measuring these interfaces with high precision guides the optimization of assembly reflow profiles.
Solder joint reliability is evaluated through the observation of micro-cracks and void distributions at these boundary regions.
