The thermal conductivity data provided by the manufacture are not always sufficiently accurate, and not available for newly formulated materials. However, it is crucial to obtain precise data of the thermal conductivity for low (less as 0.2 $\mathbf{W}\ \ \mathbf{m}^{-1}\ \ \mathbf{K} ^{-1})$ thermal conductivity materials where measurement errors have significant impact. There are several experimental methods to measure the thermal conductivity of insulating materials. These methods can be generally divided in two broad groups: steady-state and transient methods. In our work, we compared the results of thermal conductivity obtained by 3 different methods for the in-house formulated thermally insulating xerogel - epoxy composite adhesive. We performed the steady-state thermal conductivity measurements in vacuum chamber with low pressure of 7 10–9 mbar to suppress the conduction and convection losses. The results obtained by that method were compared with data obtained using two transient methods, a laser flash analysis (LFA) and an infrared (IR) thermography method. The LFA and IR thermography are indirect methods and require at least three independent measurements to obtain the thermal conductivity. The measurements error is larger than for the steady-state method. Additionally, to that, the IR thermography method exhibits several practical complications to realize necessary conditions of thermal transfer. That results in possible measurements errors and makes it not possible to obtain the thermal conductivity accurately. The steady-state and LFA methods can be used for the characterization of the thermal conductivity for low thermal conductivity materials such xerogel-epoxy composites.
The paradigm change from empirical lifetime models to a physics-of-failure based approach for automotive power electronics is driven by need for higher power densities. Hence, the usage of wide-bandgap semiconductor materials is necessary. This is accompanied by higher requirements on the packaging technologies, especially the die attach, in terms of electrical, thermal and mechanical properties. A die attach material meeting these demands is sintered silver which is already widely-used in automotive power electronics. In this study, passive thermal cycling experiments for different die sizes are performed and corresponding finite element simulations are used to find relative correlations.
High power wiring of power generators is an expensive affair that needs more attention. The cost of replacement after all paths are pulled and covered is high, and the defect is not always visible such as squeezing or bending but hidden. Therefore, due to the need for electrical testing, almost 80% of all tests performed in power systems are related to insulation quality testing. This is much more cost-effective than changing the wiring later. Most electrical equipment in industrial and commercial power systems uses 50 or 60 Hz AC voltage, depending on the range. So, using an AC power source to test insulation seems a logical choice. At the same time, however, isolation systems are extremely capacitive, which is one of the reasons that DC testing has found a large niche in this technology. In this paper, we present the implementation of a DC power supply adjustable between 0 and 500 V DC used for underground cable insulation testing.
This paper explores the possibility of using the power of the wind created by a car-in-motion for charging the car batteries. When a vehicle is moving even in a still atmosphere, a wind will act on a turbine mounted on the vehicle, this wind is called further relative wind. We study the possibility of using only the power of relative wind. The main disadvantage of electric and hybrid cars is the limited capacity of their storage batteries which impedes them from covering long distances. The obvious advantages of electric cars are canceled by the limited amount of energy stored in their batteries. Also, it is known that the conversion of an energy into another always comes with losses; therefore, a perpetuum mobile is not possible. We do not try to violate this principle, but we try to increase the efficiency of a wind turbine mounted on a car in motion. The wind turbine must be mounted on the vehicle chassis in a way to satisfy the aerodynamic and aesthetic criterions. So, the turbine system shall charge the car propulsion battery without creating supplementary friction. Results regarding the impact of the relative wind on the car conduct are analyzed using software named ANSYS and experimental tests and they are exposed in present paper. The base of this research is to demonstrate if the relative wind is sustainable to charge the battery in motion even for small improve.
Along with the large scale implementation of 5G networks a number of crucial technical challenges are still under development. Some of these are concerning the packaging and module developments, where the implementation of a large number of signal connections compatible with high data rates, the use of novel RF materials and finally new process approaches are the main issues to be tackled. Within the European funded project SERENA, an integration platform based on printed circuit board (PCB) embedding technology was developed. The technology enables the reduction of module size, system power consumption, design time, and complexity. At the same time improved performance and transmitted output power were achieved. In particular, by PCB embedding integrated RF electronic modules containing ICs for RF signal generation in very close proximity to the antennas were realized in a single package, thus minimizing the signal path losses. In the framework of the project, new materials suitable for the embedding of RF-components are used in combination with high gain GaN and SiGe dies. In this way a scalable System-in-Package operating at 39 GHz was ultimately implemented. In the course of the project a low and a high power module have been investigated. A functional low power module was fabricated at Fraunhofer IZM. Two process technologies had to be adopted (1) a combination of novel RF laminate and high-end prepreg materials to embed the dies into the build-up of the PCB and (2) the electrical connection of 3 µm Au contact pads by laser drilling and electroplating. Electrical test structures were fabricated in parallel to assess the electrical performance of package configuration and technology. Package interconnects and integrated patch antenna arrays were designed based on simulations with a 3D full-wave EM simulator (AnsysEM HFSS). The simulated structures were fabricated and measured using a network analyzer. The very short interconnection signal path between the passive and active elements realized in the PCB embedding technology achieve very low insertion (less than 0.4 dB) and return loss (better than 20 dB).The antennas in the package designed and fabricated using the PCB embedding technology achieved a wide bandwidth (3.1 GHz) with a peak gain of 8.8 dBi. Mutual coupling less than - 20 dB is obtained over the entire frequency range of interest between the elements of the antenna, thus making it suitable for beamforming. The approach proved to be well suited for the fabrication of 5G System-in-Package RF modules. The paper will give a detailed description of the fabrication processes and will discuss the technological approaches in depth. A brief overview of the electrical results will be given.
The electrochemical deposition is an additive, easy, cheap, and reproducible method to deposit different types of materials including metals, polymers, metallic oxides, chalcogenides, etc. As a general condition, this method is used to deposit one type of material onto a conductive another. Due to its remarkable properties (especially electrical conductivity, redox activity and environmental stability), polyaniline (PANI), an intrinsically conducting polymer, is a versatile material with potential applications in manufacturing of many devices such as chemical sensors, biosensors, actuators, supercapacitors, display device electrodes (electrochromic devices), photonic devices, drug delivery devices, passive or active electronic components, organic light emitting diodes, energy harvesting devices (especially solar cells), fuel cell devices, printed circuit board manufacturing, rechargeable absorbers, etc. In present paper we present the results obtained for synthesis of porous layers of polyaniline deposited by anodic electrochemical polymerization onto screen printed electrodes of gold on alumina 96% substrate. After the electrochemical synthesis, Co, Mn, Fe and Sn oxides were incorporated into the polyaniline matrix by chemical precipitation. The working conditions, electrical and physico-chemical properties of the deposited layers are presented in the paper.
In this paper, the development of FOWLP-based antenna arrays for 6G D-Band MIMO applications is presented. The proposed array consists of five patch elements, which are connected to each other to create a 1x5 series fed antenna array. The array was designed, simulated and fabricated on 150 µm mold substrate material at 140 GHz. The amplitude tapering method was applied to the array to suppress the high side-lobes levels. Finally, return loss and radiation patterns radiation of the proposed antenna array were measured and compared with simulated results. Very good correlation between simulation and measurement is obtained.
New LED technologies development is allowing the development of better performance glare-free beam modules in automotive lighting. Yet the thermomechanical fatigue and failure behavior of the LED packaging in the lighting module is affecting the reliability of the LED system by failure at the solder joint. Passive thermal cycling is widely used to evaluate solder joint reliability. Simulation tools allow us to predict the reliability of solder joints by knowledge of the fatigue life. However, during active thermal cycling, the effects of self-heating generate thermal gradients between the LED junction and the substrate, which can decrease the lifetime. Reliability in active thermal cycling is validated through subcomponents and components levels to ensure the reliability of the lighting module. In this work, we are presenting a thermomechanical study to predict the solder fatigue behavior under active thermal cycling by simulation of LED PCB packaging. The time dependent temperature field during active power cycling of a LED packaging with turn indicator is analyzed. Thermal transient and stationary simulations are made. Alternative current signal representative of turn indicator (AC) and constant Current (CC) conditions are considered. Based on the temperature evolution through the package and solder the gradient of temperature is used to evaluate the strain in a 1D model through the package by thermal expansion. Then a thermal simulation coupled with thermomechanical model allows determining the most damaging condition. Finally, a comparison between a passive thermal cycle and an active thermal cycle is made to detect the impact of a temperature gradient during active thermal cycling on fatigue life trends.
Higher input/output (I/O) density and fine pitch bumping are becoming crucial due to higher performance requirements and a decrease in structure size in electronics such as integrated circuits (ICs) [1-3]. Currently, the focus has been put on fine pitch copper (Cu) pillar bumps due to superior conductivity, and mature technology with Cu solder bumps [4, 5]. However, Cu requires under bump metallization (UBM), and bonding substrate choice is limited to material hardness (343–369 MPa) [6, 7]. A completely new approach would be Aluminum (AI) pillar fabrication, which enables fewer fabrication steps and bonding at room temperature. It is CMOS compatible and material wise cheaper than Cu or gold (Au). Such structures on a chip can later be integrated using ultrasonic bonding, which is fast and less energy-intensive compared to Thermo-Compression Bonding (TCB) [8].
This paper describes the challenges associated with ultra-high thickness single coated (UHTSC) films, in general, and the specific problems and solutions for UHTSC on the spin-coating process. Here, with a single coating, photoresist (PR) films with a thickness above 170 um were achieved for the purpose of building demonstrative high aspect ratio structures. A custom dispensing setup to prevent, or reduce, the formation of air bubbles is presented and a film thickness (FT) measuring technique were developed in order to achieve the proposed goal. The dispensing setup was based on microfluidics theory and a fluidic to electronic device analogy was applied. Of the two fabricated samples, one has a FT of 176.5 um and a non-uniformity (NU) of 23.5% over the entire wafer and 8.3%, over an active area of 190 mm diameter. For the other sample, these values are 170.6 24.1% and 12.6%, respectively. Remarkably, the process presented in this work was achieved with a commercial PR specified for the 15~100 um range, surpassing by almost two-fold the supplier's limit. This opens exciting perspectives for the cases where the base material is targeting even thicker films.
A new concept for anisotropic conductive adhesive (ACA) based on a predefined number of electrically conductive particles captured at individual interconnects is introduced. Capillary assembly method is applied to deposit conductive particles on a patterned polydimethylsiloxane (PDMS) carrier. These particles are transferred to electrical pads on a substrate whose surface is laminated with a non-conductive adhesive film. A die is then aligned and thermocompression bonded to the substrate. A yield as high as 97.8% is obtained for the particle deposition process while the yield of transferring particle process is almost 100%. Bonded samples achieve 63% of interconnects having the exact predefined number of conductive particles. The measurements of electrical resistance and contact area between particles and substrate indicate the formation of electrical paths between the electrical pads and conductive particles. This work has demonstrated the feasibility of ACA interconnects with conductive particles localized only between mating electrical pads on the die and substrate, but not outside these desired locations. Such interconnection approach minimizes the risk of short-circuit and open-circuit failures in fine-pitch applications.
After two years of the COVID-19 pandemic, the disruption in Higher Education, especially in Engineering Education 4.0, has taken place. The world is more interconnected than it has ever been. How do we prepare students for it? What makes learning with virtual collaboration efficient? In our paper we took a closer look at online teaching and learning in the period from October 2021 to June 2022, emphasizing the teacher's and students' experiences. Two exemplary courses designed with agile and design thinking methods illustrate the approach: the University of Passau and the University Politehnica of Bucharest. After the implementation of the Education 4.0 model with agile methods for future thinking, at the University of Passau, over 80% of students collaborated actively during the hybrid seminar. This paper opens the way to innovation with agile methods for virtual collaboration in Engineering Education 4.0.
Epoxy resins are commonly used for the encapsulation of electronic components in electronic packaging processes. The chemical crosslinking process and therefore the curing of these resins during processing have a significant influence on the production and finally on the quality of the components. To follow the chemical changes during the process, a fourier-transform infrared (FT-IR) sensor was integrated into a molding press to measure in-situ infrared spectra during the process. The feasibility and reproducibility of this measurement method is presented. The spectra generated in the process show changes in absorption bands around 916 cm -1 and 1230 cm -1 equivalent to laboratory measurements, indicating the chemical crosslinking process. Several tests show that the repeatability of this measurement method is very good. Further, the influence of different molding temperatures on the generated infrared spectra was investigated, and no significant change in the width, intensity or shift of the bands could be detected. However, the crosslinking of the material is affected by temperature, with low temperatures leading to a slower crosslinking process. With the use of a model, it is possible to estimate the residual enthalpy of the material based on the spectra, which allows subsequent process optimization.
The training/course development of MicroElectronics Training, Industry and Skills (METIS) project is carried out across an online education platform, called Moodle. The course will cover the knowledge about materials and technologies relating to semiconductor chips including, but not limited: properties of semiconducting materials, elemental semiconductors, compound semiconductors, doping, diffusion, ion-implantation, fabrication of semiconductor wafers, Layer deposition and doping technologies, construction of transistors, patterning and device structuring of semiconductor wafers. The course overviews the material related failure mechanisms in microelectronics, and the analysis techniques aiding the reveal of these failures root causes. Furthermore, the course covers also basic knowledge of big data analyses in materials engineering.
For optimized performance of the semiconductor switch in a power electronic module a uniform current distribution in the active volume of the chip is desirable. Since the bottom side of the semiconductor die is fully connected to a substrate by a soldered or even a sintered layer, the vertical current distribution is mainly determined by the top side interconnection technology and the ability of the top side aluminum metallization to spread the current in lateral direction. The focus of this paper is on the influence of the metallization and the top side connection, realized by heavy wire bonds. Sheet resistance and roughness measurements were taken on power modules, aged by active power cycling, in order to evaluate degradation during regular operation. Voltage mapping measurements across the metallization layer during operation were correlated to finite element simulation results, revealing inhomogeneities in the current density distribution in the metallization layer as well as the semiconductor die.
The growing demands for high power density in inverters for electric vehicles have led to an increase in the operating temperature of power devices. Die attachments with high-temperature reliability in high-power device packaging are thus under improvement. In this study, a Ag10Sn alloy paste is developed. The Ag10Sn alloy powders are prepared by mechanical alloying of Ag and Sn powders with a series of milling speeds for 2, 4, and 10 h to determine the optimal milling parameters. Characterization of the powders is carried out by XRD and SEM. The die bonding process is accomplished between Ag-metalized Cu substrates. The structural integrity of the Ag10Sn bond line is investigated by thermal aging at 300°C. The bond line is comprised of homogenous Ag solid solution with limited pore coarsening during aging. The high shear strength of the Ag10Sn bond line is obtained at 53 MPa after 1000 h of aging. The results show that bond lines of the Ag10Sn solid solution phase possess good mechanical properties and low porosity under high temperatures. In addition, the bond line could prevent Cu substrate from forming Cu 2 O layer. Consequently, Ag10Sn alloy paste possesses high thermal reliability and is thus a promising die attachment for high-power device packaging.
To alleviate the heat dissipation issue of through silicon via (TSV) integrated ion trap on glass interposer, a ceramic pin grid array (CPGA) with built-in redistribution layer (RDL) is demonstrated to locate the trap directly. This patterned RDL has internal connection to the backside CPGA pin, facilitating locally flexible signal rerouting. The glass interposer with poor thermal conductivity can be eliminated. The design consideration and fabrication steps of customized CPGA are presented. The leakage current and parasitic capacitance are characterized using J-V and C-V tests respectively. It is found that the customized CPGA has a superior insulation performance: the averaged resistance between two arbitrary RDL pads is 3.2x1012 Ohm, which is three orders of magnitude higher than that of TSV integrated ion trap itself. The capacitance between RF and central DC RDL pads is ~1 pF, indicating low RF loss. Based on finite element modelling result, the temperature increase of trap surface on customized CPGA is able to maintain ~3 K at a given power of 0.1 W, significantly lower than that of trap on glass interposer (~35 K). A compact assembly architecture with good thermal dissipation capacity is demonstrated for ion trap devices.
Polyethylene Terephthalate (PET) is an excellent material for transparent display products that are flexible, easy to process and low cost. However, conventional flip chip bonding processes using thermo compression (TC) is limited to warpage due to high shrinkage of PET materials. Laser Assisted Bonding (LAB) technology can be an excellent solution to this warpage of PET by controlling temperature and time during the flip chip bonding process. In this study, an epoxy-based solder paste (named Hybrid Underfill) was developed to integrate LED devices into flexible substrates.
D-band substrate integrated waveguide (SIW) bandpass filter with slots based on mold compound was manufactured and measured. The investigation shows the high potential of SIW filters to be integrated in packages using fan-out wafer level packaging (FOWLP). The manufactured sample was inspected using microscope to validate the measurements. The second order filter configuration demonstrates good selectivity properties. The measurements and full-wave modelling demonstrate a very good correlation in terms of magnitude and phase of return and insertion losses.
Lithium-ion batteries are the main technology on which the global green energy initiative has been based in recent years. As a source of energy, they have a high energy density and long life. Their use is relatively safe and production costs are relatively low. They are currently used in various types of electric vehicles, space applications, and much of the consumer portable electronics. Battery Prognostics and health management depends on State of health (SOH) monitoring. SOH is the main parameter for the safety and reliable work of the batteries. In most cases, it is determined by measuring the impedance of the battery. This is related to some limitations arising from the method of measurement, which is contact and requires the connection of multiple measuring wires to the batteries. In this article, we present a model to determine the SOH of the battery which uses the rate of increase of battery temperature during the discharge cycle. The study is carried out by a project team consisting of scientists from Plovdiv University and Technical University - Sofia within a project funded by the Bulgarian Research Fund. The proposed model is based on an in-depth analysis of the physical laws describing the processes of raising the battery temperature during its operation. Attention is paid to the relationship between these processes and battery degradation. For the purposes of the study, we have used the NASA Battery Data Set. Based on these data, the relationship between the rate of increase of the battery temperature during its discharge and the number of discharge cycles is derived, which is associated with changes in its capacity and degradation. To determine the rate of increase of the battery temperature over time, the first derivatives of the temperature function at the same discharge current but after a different number of discharge cycles are calculated. To illustrate the process in detail, these dependencies are presented graphically. Since the rate of increase of the battery temperature depends on the magnitude of the discharge current and the ambient temperature, the dependences for two operating modes are derived: discharge current with magnitude 2A and 4A at an ambient temperature of 24 degrees Celsius. The proposed model for determining the SOH of the battery using the relationship between the rate of change of its surface temperature and the number of discharges in the process of its operation is an accurate tool that can help to ensure the safety, quality, and reliability of the battery.
