4286009

Dual-mode BLS/LFR microscopy for mechanical property imaging of polymeric materials

Date
August 18, 2025

Brillouin light scattering (BLS) spectroscopy and low-frequency Raman (LFR) spectroscopy are powerful techniques for non-contact, non-destructive measurement of the mechanical properties of soft materials. BLS can be used to investigate phonon modes which relate to elasticity and viscosity, while LFR enables the probing of collective vibrations and relaxations, which relate to dissipative modes and properties such as polymer toughness. BLS and LFR are optical techniques that rely on measuring inelastically scattered light, which allows for the integration of these techniques into optical microscopes, enabling the local measurement of mechanical properties. Despite these advantages, these techniques are not routinely employed as basic characterization tools by the polymers and soft matter research communities, especially in the emerging area of polymers for next-generation semiconductor packaging technologies. Furthermore, there are few reports of combining BLS and LFR techniques into a single microscopy platform, an approach that allows for more comprehensive mechanical property measurements of polymers.

In this work, the design of a combined BLS/LFR microscope capable of measuring local mechanical properties such as elastic moduli and Poisson’s ratio, as well as LFR spectral features, is presented. The microscope integrates an environmental chamber with controllable temperature and humidity, allowing for in situ measurements of soft materials. Semiconductor packaging materials are used as a model system to demonstrate the microscope capabilities. This includes in situ cure monitoring, post-cure operating condition monitoring, and mechanical property imaging. While the investigation of semiconductor packaging materials is the example application presented in this study, the BLS/LFR microscope, as well as the microscope design in general, can be applied to other fields of study in which the mechanical property measurements of soft materials are challenging.

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