FIB-SEM based 3D tomography of micro-electronic components: Application to automotive high-definition LED lighting systems

Abstract

In new high definition lighting modules, assembling more than thousand elements (pixels) with a single mm-sized motherboard is achieved by reflow soldering. Lead-free solders may constitute a weak part of electronic components and LED assemblies. During reflow, the distance between pixels and motherboard controls the solder heights (10 μm). After assembly, all the pixels are in a single plane. To ensure constant solder heights, this plane has to be parallel to the motherboard. A small disorientation during reflow may lead to severe solder damage prior to any use of the opto-electronic component. Present work presents a novel non-destructive method for characterizing any chosen solder in the assembled component without unpacking the latter.A femtosecond motorized laser source is used for digging a hole in the LED above the selected solder. Then a Focused Ion Beam facility allows to mill around this specific solder. The same FIB facility allows making several hundred slices of controlled thickness and orientation in the solder material. During this slicing operation, high-resolution inspection is done by FEG-SEM (Field Emission Gun - Scanning Electron Microscope) imaging. 3D tomographic reconstruction of the solder is obtained by classical commercial software AVIZO. Finally, 3D damage in solder material is illustrated by example results.