Objective Semiconductor packaged devices often require failure diagnosis under the constraints of noncontact measurement, no package opening, and rapid hotspot localization. In practice, defect induced thermal signatures can be weak and may be obscured by direct current background radiation, slow temperature drift, and asynchronous disturbances. In addition, thermal diffusion in multilayer package structures reduces spatial contrast, which limits localization robustness. This work proposes an electrically excited infrared thermography method that uses internal Joule heating as a defect related heat source, enabling hotspot enhancement and localization without decapsulation.

Methods A unipolar sinusoidal electrical excitation with a direct current bias is applied to the specimen, so that defect related conductive paths generate a periodically modulated Joule heating component at the fundamental excitation frequency. An infrared camera records the surface temperature sequence. Pixelwise dual channel orthogonal coherent demodulation is performed by discrete correlation with in phase and quadrature reference signals over an integer number of excitation periods, and the fundamental frequency amplitude plot and phase plot are reconstructed (Fig.1). This demodulation suppresses the direct current background, slow drift, and asynchronous noise. For objective comparison across different excitation conditions, a peak gradient based self calibrated spatial partition is introduced to determine a characteristic hotspot scale, and a coupled metric that jointly reflects peak significance and spatial focusing is constructed for parameter selection; the defect cluster center is obtained using a lightweight unsupervised clustering step (Fig.5, Fig.6).

Results and Discussions Experiments were conducted on an electrically overstressed Microcontroller Unit (MCU) specimen in a quad flat package, and the reconstructed amplitude plots exhibit a single peak distribution that is close to Gaussian around the defect; the peak position remains consistent across excitation conditions, demonstrating stable localization (Fig.4). Frequency sweep results show that increasing the frequency markedly reduces the core hotspot area, indicating enhanced spatial focusing (Fig.7(a)), while the peak significance decreases at higher frequencies (Fig.7(c)). Nevertheless, the coupled metric increases overall with frequency (Fig.7(b)), indicating that the gain from spatial focusing exceeds the loss in peak magnitude under the tested conditions. Voltage sweep results indicate that the core area varies weakly with the excitation amplitude and shows larger scatter (Fig.8(a)), whereas the coupled metric exhibits a clear nonlinear trend across the tested range (Fig.8(b)), consistent with the combined influence of peak magnitude and spatial diffusion (Fig.8(c)). Phase plots show a stable phase anomaly region across multiple frequencies (Fig.9). The phase increases with frequency in a nonlinear manner and tends to saturate at higher frequencies (Fig.10), and phase profiles provide repeatable extrema that can serve as an auxiliary and more robust cue for localization (Fig.11, Fig.12). Decapsulation inspection, bare die observation, and emission microscopy (EMMI) comparison confirm that the localized infrared hotspot corresponds to the electrically abnormal region (Fig.13).

Conclusions An electrically excited infrared thermography approach combined with orthogonal coherent demodulation is developed for hotspot localization in semiconductor packaged devices without decapsulation. Joint amplitude and phase analysis supports objective parameter selection and improves localization robustness. Under the experimental conditions of this work, a lock in frequency range of 0.5 Hz to 1.25 Hz and an excitation amplitude range of 1.0 V to 1.4 V are more favorable for stable defect detection and localization.