Elemental Distribution Analysis of Electronic Components

Micro-XRF - High Spatial Resolution, High Elemental Sensitivity

Microelectronic components are of increasing complexity. The size and distances of the surface mounted devices (SMD) and integrated circuits (ICs) are getting smaller and the wires and connections are implemented in several layers within the printed circuit board (PCB). Therefore, analytical methods to approach these sort of samples need both, a high spatial resolution and the capability to look into the depth of the sample. Micro-XRF is an imaging technique which combines spatial resolution of roughly 20 µm with a very high elemental sensitivity for most metals. It can therefore be a companion in the complete life cycle of electronic components, from R&D for novel designs and materials to recycling of precious metal components. The main application is failure analysis and quality management including layer thickness measurements; for instance for Au contacts and bond pads, or solder bumps. The method can be used for a qualitative pre-screening of RoHS- and WEEE-relevant elements. Looking for the abundance and locations of precious metals or harmful substances support efficient waste treatment or recycling of electronic components.

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Populated PCB of a mobile phone. The IC‘s plastic casings are transparent to the higher-energy radiation of the heavy elements like gold, silver and also arsenic. The bond wires with their diameters of only about 10 µm are well resolved without the need to lap down any parts of the sample.

These two images of a RAM chip display the intensities of backscattered low- and high-energy X-rays. The Compton scattering process is more pronounced in lighter matrix. Therefore heavy matrix appears darker in this picture. The low energy photons are scattered at the surface of the sample and (with their energetic overlap with the chlorine fluorescence) are sensitive even to fingerprints on the plastics. Also color pigments affect the scattering properties of the sample. The lower picture is created from mapping the intensity distribution of high-energy scattering. These photons interact in greater depths and within the ICs they still reveal the intricate bond wire structures. With the energy-dispersive SDDs, the information on the scatttered X-rays are taken from the same spectra as the fluorescence signals of the individual elements.