Three-fiber quantum dot probe for hotspot thermometry in electronic packaging

Thermal management in next-generation electronic packaging would benefit from in-situ monitoring of microscopic hotspots with sub-millimeter spatial resolution and electromagnetic interference (EMI) immunity. In this study, we demonstrate a localized hotspot thermometry system based on a specialized three-fiber probe combined with temperature-sensitive fluorescent quantum dots (QDs). A fiber-coupled UV LED excites the QDs deposited on the fiber tip, and their fluorescence is collected by two high numerical aperture (NA) fibers. Experimental benchmarks demonstrate that the proposed 1-excitation-2-collection topology achieves a superior signal-to-noise ratio (SNR) compared to standard single-mode fiber (SMF) designs by suppressing parasitic Fresnel reflections through spatial decoupling while maximizing collection efficiency. The collected emission wavelength and amplitude are used to determine the absolute temperature. Three probe configurations were evaluated, and perovskite quantum dots (PeQDs) were compared with InP/ZnS QDs. The PeQDs exhibit a temperature-dependent emission amplitude with high linearity within the 21-43^∘C range. For the InP/ZnS QDs, the wavelength shift of the peak emission was utilized, enabling thermometry at higher temperatures up to 74^∘C. The proposed sensor provides accurate temperature data independent of surface emissivity, offering a robust alternative to infrared thermography for the characterization of complex heterogeneous electronic systems.