Epoxy molding compound (EMC) is widely used for encapsulating automotive electronics. Among all of the components of an electronic package, EMC is most exposed to the atmosphere, and thus undergoes aging. During high-temperature operation, EMC is oxidized, which alters its mechanical properties, and thus can affect the reliability of electronic components. This chapter focuses on four key aspects of EMC oxidation – (1) the growth of EMC oxidation layer, (2) the mechanical properties of oxidized EMC, (3) the effect of oxidized EMC on thermomechanical behavior of a molded package, and (4) the effect of EMC oxidation on solder joint reliability. This study utilizes various experimental characterization techniques as well as finite element simulation-based analysis.@en

The piezoresistive silicon based stress sensor has the potential to be part of the Digital Twin implementation in automotive electronics. One solution to enforce reliability in digital twins is the use of Machine Learning (ML). One or more physical parameters are being monitored, while other parameters are projected with surrogate models, just like virtual sensors. Piezo-resistive stress sensors are employed to measure the internal stresses of electronic packages, an Acquisition Unit (AU) to read out sensor data and a Raspberry Pi to perform evaluation. Accelerated tests in air thermal chamber are performed to get time series data of the stress sensor signals, with which we can know better about how delamination develops inside the package. In this study stress measurements are performed in several electronic packages during the delamination. The delamination is detected by the stress sensor due to the continuous change of the stiffness and the local boundary conditions causing the stresses to change. Although, the stress change in multiple cells can give enough information if it is delaminated or not, its delamination area location is unknown. Surrogate models built upon Neural Networks (NN) and Finite Element Method (FEM) are developed to predict the out of plane stresses at the delaminated layer. FEM simulation models are calibrated with Moiré measurements and validated at the component and PCB level with stress difference measurements. Simulation delamination areas are constructed based on the Scanning Acoustic Microscope (SAM) images, and are also validated with the equivalent stress measurements. In the end the surrogate model is predicting the out of plane stress in the adhesive layer. The results show good correlation when compared to the SAM images.

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Epoxy-based molding compounds (EMC) are widely used to encapsulate automotive electronics. Under high temperature operation, EMC is oxidized and undergoes degradation in mechanical properties. This can alter the thermomechanical behavior of encapsulated electronic components, and thus can affect their reliability. Three key aspects of EMC oxidation in the context of microelectronics reliability are presented in this paper – (1) degradation of EMC specimens is studied under high temperature aging at three different temperatures – 170°C, 200°C, and 230°C for up to 1500 hours and the oxidation growth is documented as a function of aging duration and temperature using a fluorescence microscope; (2) critical thermomechanical properties of oxidized EMC (viz., elastic modulus, thermal expansion coefficient, and glass transition temperature) are experimentally characterized using fully-oxidized specimens; (3) the effect of EMC oxidation on thermomechanical behavior of an electronic package is investigated by comparing the deformation of a thermally aged package with that of a pristine package under a thermal cycle. This study indicates that EMC oxidizes rapidly during early stages (≈ 24 hours) of exposure to high temperature, and the oxidized layer exhibits significantly different thermomechanical properties. Thus, thermal aging develops a much stiffer package behavior, which is crucial for an accurate reliability assessment.

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It is expected that more and more complex (integrated) automotive electronics will be adopted in systems. These advanced electronics are critical for passenger safety. Documenting the in-situ loading is, thus, very important for accurate reliability prognostics. In this study, we propose a piezoresistive stress sensor to detect the in-situ loading of an automotive electronic control unit (ECU). A load metric directly related to the in-situ loading is defined by considering the in-situ stress values of twelve measurement cells in each sensor. The sensor and the proposed load metric are implemented to document the in-situ loading that results from the local coefficient of thermal expansion mismatch between the electrical components and printed circuit board (PCB) in advanced ECUs. The validity of the proposed metric is corroborated by failure analysis of solder joints of multilayer ceramic capacitors (MLCCs).

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In the automotive industry, epoxy-based molding compounds (EMCs) are often used to protect not only single IC packages but also entire electronic control units (ECUs). The EMC undergoes thermal aging during the operation-lifecycle of its parent electronic package. The thermal aging oxidizes the EMC, which can alter its mechanical properties significantly. Understanding the oxidation phenomenon of EMC and its effect on property changes is critically required to predict the reliability of ECUs subjected to harsh environments. In this study, the oxidation phenomenon of EMC is characterized experimentally by measuring oxidation growth rate and the mechanical properties of oxidized EMC. In the first task, EMC samples are subjected to three different high temperature storage (HTS) conditions - 170 °C, 200 °C and 230 °C. The thicknesses of the oxidized layers are measured as a function of storage time (from 0 to 1500 hours) using a fluorescent microscope. The oxidation growth rates at the storage temperatures are determined from the thickness measurements, and they are subsequently used to determine the activation energy of the growth rate. In the second task, thin samples (300 μm thick) are subjected to a HTS condition until they are fully oxidized. Then, critical thermo-mechanical properties of oxidized EMC, including coefficient of thermal expansion (CTE), glass transition temperature, and modulus of elasticity, are measured using digital image correlation (DIC) and dynamic mechanical analysis (DMA), respectively. The detailed procedures of the experimental characterization are presented together with the test results. Their implications on the ECU reliability is also discussed.

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