Developing reliable and efficient power semiconductors is essential to realizing a sustainable future. Packaging materials for high-power applications are electrically overstressed, are exposed to harsh environmental conditions, and are subjected to heightened temperature swings, thereby compromising the device’s stability and longevity. In this dissertation, a series of experimental methodologies were explored for monitoring the package conditions, particularly the die-attach interface, which transmits the necessary electrical, thermal, and mechanical signals from the device to the system. Furthermore, advanced thermal management strategies were investigated to circumvent concentrated microthermal hot spots and improve the device’s power rating.@en

Prognostic monitoring of power quad flat no-lead (PQFN) packages with four distinct silver pastes, each varying in material composition (pure-Ag and resin-reinforced hybridAg) and sintering processes (pressure-assisted and pressureless), was investigated in this study. The PQFN packages with silver sintered die-attach materials were subjected to thermal cycling tests (?55 ° C to 150 ° C), and the performance degradation was evaluated based on the following metrics: 1) electrical ON-state resistance RDSon monitored periodically at specific thermal cycling intervals and 2) transient thermal impedance Zth(t = 0.1 s) monitored online during thermal cycling. These measurements were further validated using acoustic microscopy imaging and cross-sectional inspection. The pressureless Ag-sintering material demonstrated comparable performance to pressure-assisted Agsintering, with a dense microstructure, and consistent electrical and stable thermal performance. Whereas the pressureless resinreinforced hybrid-Ag material exhibited degradation with a relative increase of 33% in RDSon, 38% in Zth(t = 0.1 s), and 67% delamination of the die-attach interface over 1000 cycles. These findings suggest that pressureless Ag-sintering may offer a viable alternative to pressure-assisted methods for lead (Pb)- free die-attachments, while resin-reinforced hybrid-Ag requires further development for improved thermomechanical reliability..

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Resin-reinforced Ag sintering materials represent a promising solution for die-attach applications in high-power devices requiring enhanced reliability and heat dissipation. However, the presence of resin and intricate microstructure poses challenges to its thermal performance, and improvement strategies remain unclear. This work utilizes 3D FIB-SEM nanotomography to reconstruct the microstructure of this material under various process conditions. The analysis reveals that, even with an Ag volume fraction as low as 47.3%, Ag particles form a robust 3D network. Geometric tortuosity quantifies the effect of different sintering conditions on the Ag particle network in all spatial directions. Effective thermal conductivity is simulated based on realistic microstructure models. Results show a significant negative correlation between tortuosity and effective thermal conductivity. Increasing sintering temperature in Model B notably reduces tortuosity and enhances effective thermal conductivity. Sensitivity analysis underscores the dominant role of Ag volume fraction in regulating effective thermal conductivity. Finally, transient thermal impedance measurement of this material as a thin die-attach layer in actual high-power devices demonstrated its application potential. This article strives to explore the relationship between process, microstructure, and thermal properties of this material to provide a reference for further development.

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This article introduces an online condition monitoring strategy that utilizes a transient heat pulse to detect package thermal performance degradation. The metric employed is the temperature-dependent transient thermal impedance "Zth(t, Tamb)."The proposed methodology offers quantitative insights into package thermal performance degradation and effectively pinpoints the presence of multiple failure mechanisms. A thermal test chip assembled in a power quad flat no-lead package is used in this study to demonstrate the methodology. The packaged devices are first characterized to determine the transient pulse duration, a critical parameter to monitor a specific region of interest. Subsequently, package thermal performance degradation is continuously monitored online during thermomechanical cycling lifetime experiments. The validity of the measurement results is later confirmed through acoustic imaging and cross-sectional analysis. The changes observed in Zth(t, Tamb) over thermal cycling correspond to the delamination of the active metal layers on the die and cohesive failure on the die attach. This article further includes a comparative summary, highlighting the distinctions between the proposed and industry-standard test methods. In conclusion, the importance of online condition monitoring to detect early signs of failure is emphasized, and the proposed methodology s practical applicability in real-life scenarios is briefly discussed.

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The increasing awareness of environmental concerns and sustainability underlines the importance of energy-efficient systems, renewable energy technologies, electric vehicles, and smart grids. Hence, stringent constraints and safety regulations have been prompted to meet reliability standards in power electronics. This chapter provides a comprehensive outlook on the current state of power semiconductor devices, field-critical applications, dominant degradation mechanism (chip-related and package-related), and the emerging measurement techniques for reliability/condition monitoring. This chapter delves into the underlying physics behind each reliability measurement method reviewed. A comparative summary of cost, complexity, online monitoring capability, accuracy, and intrusiveness is provided to enable readers to make informed decisions about the measurement methods. This chapter emphasizes the significance of early fault detection through online monitoring, as it can effectively reduce system downtime for seamless non-interruptive operation.

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Silver sintering offers a promising landscape for Pb-free die attachment in electronics packaging. However, the sintered interface properties are highly process-dependent and deviate from bulk silver properties. Conventional measurement methods do not adequately capture the die-attach application geometry. Hence, this study introduces a novel methodology for characterizing thin bond-line interfaces with high-conductive materials. The transient heat flux impedance ΔZth(t, Δx) was measured between two thermally sensitive devices interconnected using pressureless Ag-sintering material. A correction factor was derived, based on thermal half-space principles, to account for non-uniform heat spreading over the die-attach interface. Experimental findings estimate an effective conductivity of ∼115W/mk for the pressureless Ag-sintered interface. The measurement results were validated by measuring a SAC305 soldered interface, which exhibited ∼55 W/mK, and a non-conductive epoxy interface of ∼2.5 W/mK. Voids on the die-attach layer, resulting from material processing, were identified to influence the interface thermal behavior. An uncertainty analysis was further discussed, emphasizing equipment tolerances, measurement sensitivity, and geometrical and thermal anisotropies. The article concludes with a comparative summary of the proposed methodology against conventional methods, highlighting differences in working principle, thickness range, measurement parameters, and their advantages and limitations.@en

This study introduces a training protocol utilizing Convolutional Neural Networks (CNNs) and Confocal Scanning Acoustic Microscopy (CSAM) imaging techniques to classify Power Quad Flat No-leads (PQFN) package delamination. The investigation involves empty PQFN packages with varied substrate metallizations subjected to thermal cycling. Four delamination classes were labeled: Die-pad delamination (Class-A), Bond-pad delamination (Class-B), both Die-pad and Bond-pad delamination (Class-C), and No delamination (Class-D). Due to data imbalance, additional randomness was introduced for distribution balancing. Residual Networks (ResNet-18) based CNN model was selected for classification. Five-fold cross-validation assessed overfitting performance concerning input data size, image resolution, and batch size. The ResNet-18 prediction performance was evaluated using precision and recall metrics, with the model achieving average precision and recall scores of 0.86/1 and 0.83/1, respectively. Additionally, a comparison of delamination among different substrate metallizations was presented with Ag and NiPdAu indicating significant delamination compared to bare Cu substrate. This study pioneers the integration of CNNs with CSAM imaging for package defect detection and classification, laying the groundwork for future research to address the complex interplay of multiple failure mechanisms in functional packages.@en

Integrated Circuits and Electronic Modules experience concentrated thermal hot spots, which require advanced thermal solutions for effective distribution and dissipation of heat. The superior thermal properties of diamonds are long known, and it is an ideal material for heat-spreading applications. However, growing diamond films to the electronic substrate require complex processing at high temperatures. This research investigates a heterogeneous method of integrating diamond heat spreaders during the back-end packaging process. The semiconductor substrate and the heat spreader thicknesses were optimized based on simulations to realize a thermally enhanced Power Quad-Flat No-Lead package. The performance of the thermally enhanced PQFN was assessed by monitoring the temperature distribution across the active device surface and compared to a standard PQFN (without a heat spreader). Firstly, the thermally enhanced PQFN indicated a 9.6% reduction in junction temperature for an input power of 6.6W with a reduced thermal gradient on the active device surface. Furthermore, the diamond heat spreader's efficiency was observed to increase with increasing power input. Besides, the reliability of the thermally enhanced PQFN was tested by thermal cycling from -55°C to 150°C, which resulted in less than 2% thermal degradation over two-hundred cycles. Such choreographed thermal solutions are proven to enhance the packaged device's performance, and the superior thermal properties of the diamond are beneficial to suffice the increasing demand for high power.

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Resin-reinforced silver (Ag) sintering material is an effective and highly reliable solution for power electronics packaging. The hybrid material’s process parameters strongly influence its microstructure and pose a significant challenge in estimating its effective properties as a thin interconnect layer. This research demonstrates a novel 3D reconstruction methodology for the microstructural investigation of the resin-reinforced Ag sintering material from OverMolded Plastic (OMP) packages. Based on the reconstructed models with different sintering parameters (temperature and time), the fraction of Ag and Resin volume distribution, the connectivity of silver particles, and the tortuosity factors were estimated. A 99% connectivity of sintered Ag particles was achieved with various sintering conditions, such as 200°C for 2 hours, 200°C for 4 hours, and 250°C for 2 hours. However, coarsening of Ag particles was promoted when sintered at 250°C. Increasing the sintering time at 200°C had insignificant changes. The estimated tortuosity factor also indicated that sintering at 250°C provides the shortest heat transport path between the semiconductor die and the package substrate. In order to quantify the microstructural findings, the OMP packages’ thermal performance with different sintering conditions (temperature, time, and interconnect thickness) was experimentally assessed. Although the experimental measurements were less sensitive to the effective interface thermal resistances’, the measurement results show a good correlation with the microstructural analysis. Sintering the Resin-reinforced Ag sintering material at higher temperatures (250°C) seems to improve the package thermal performance, and increasing the sintering time at 200°C has a negligible effect.@en

With an increasing demand for high-power electronics, the need to meet stringent automotive norms and better understand the critical failure mechanisms are crucial in order to improve their reliablity. To that end, we developed an in-situ reliability monitoring setup capable of actively measuring the thermal performance of the package during lifetime testing. A Thermal Test Chip (TTC) assembled into a Power Quad Flat No-lead (PQFN) package was employed as a test vehicle for non-destructive reliability assessment. The TTC comprises resistive heaters as a heat source and resistive temperature elements for measuring the thermal response. The transient thermal behavior was evaluated based on the contribution of heat source to a temperature field, and the temperature distribution was measured at multiple spatial positions. The experimental results provide insights into the thermal properties’ influence on the thermal behavior of the package. A compact electro-thermal model based on analogies was developed to deconvolute and analyze the transient thermal measurements. The results of the compact model correlate with the experimental measurements, and the model’s accuracy was verified using finite element simulations. The development of such thermal characterization experiments and computationally inexpensive models assist in further understanding the impact of failures in advancing high-power density electronics.@en