Electrical Pads Research Articles

Compliant Interconnects Based on Single Micrometer-sized Metal-Coated Polymer Spheres.

The rapid evolution of multifunctional electronics necessitates interconnection technologies appropriate for large dies with high-density and/or ultrafine pitch input/output pins. Existing technologies face numerous challenges, including demands for bonding equipment that can deliver extremely high force as well as thermo-mechanical stresses induced in the assembled packages due to mismatched thermal expansion of materials involved. This study proposes an approach to compliant interconnects comprising single micrometer-sized metal-coated polymer spheres, being joined to mating electrodes by sintering of Ag nano ink at low temperature (140 °C) and low pressure (∼15 mN/particle). Such an interconnection technology is expected to enhance the thermo-mechanical robustness of the assembled packages as well as be capable of high-density, ultrafine pitch interconnects. Our approach demonstrates control over conductive particles during assembly, achieving a 98% success rate in individual interconnects with a single captured particle. The use of sintered Ag not only secures free-standing particles on electrical pads (with an adhesion force above 2 μN) but also results in a 15% reduction in interconnect resistance, with measured resistance as low as 0.5 Ω, compared to interconnects without Ag ink. This method presents an alternative to metallurgical joints, particularly suited for high-density, ultrafine pitch applications, offering low bonding pressure and temperature, along with improved interconnect compliance to enhance the thermo-mechanical robustness of the packages.

A Subtractive Method to Chemically Pattern Liquid Metal for Stretchable Circuits

AbstractAdvancements in biomedical research have spurred the development of stretchable electronic devices. While soft insulators are readily available, soft conductors with metal‐like electrical conductivity are rare. Gallium and its alloys, being nontoxic and intrinsically stretchable, are potentially ideal solutions. However, current additive liquid metal (LM) patterning methods face limitations in achieving high‐throughput, high‐resolution, and high‐density LM wiring. Here, a subtractive LM patterning method is developed to meet all these requirements simultaneously. The innovative method involves parallel filling a single continuous microfluidic mesh network with LM that short‐circuits all the pins and pads of a circuit, followed by parallel cutting of the unwanted short‐circuited interconnections using hydrochloric acid (HCl) vapor. Cutting locations are pre‐defined by designing narrower intersecting channels, leveraging capillary force for precise filling and cutting. The process is characterized using a multidimensional parametric study with varying LM line widths and HCl concentrations, and in situ impedance measurements to assess insulation performance. To showcase its high‐throughput capabilities, a mock circuit is used to successfully generate complex LM interconnects that connected hundreds of electrical pads. Finally, a stretchable LM circuit with a micro‐LED array is fabricated to demonstrate the practical application of this technology for massively parallel wiring in stretchable electronics.

Evaluation of Heating Pad using Electrical Heating Element for Flexitank Transportation Application

Liquid transportation is accomplished in various ways, including the use of tankers and containers. Recently, most liquid shipments have utilized Flexitank as liquid containers, where steam heating is employed to melt frozen cargo liquids. However, due to limitations and disadvantages associated with steam-type heating pads, particularly in terms of the time taken to melt the liquid, researchers are exploring alternative methods for heating liquid within the Flexitank. This project aims to investigate the possibility of implementing electrical heating pads as an option for liquid heating in liquid transportation. Various types of electrical heating pads have been studied to explore their characteristics and operational capabilities. Experimental testing has been conducted on several electrical heating pads to compare their characteristics, especially in terms of the desired temperature requirement for specific liquid temperatures, as well as current consumption for each heating pad. This study will assist in determining the best option for implementing electrical heating pads in Flexitank. The results show a promising future for electrical heating pads in Flexitank, but further study is required to examine various heating pad arrangements in actual implementation.

Enabling Low Pressure, Low Temperature, and Particle Control for Anisotropic Conductive Adhesives

AbstractAnisotropic conductive adhesives (ACAs) are the preferred interconnection technology for applications that employ large dies, flexible substrates, and ultra fine‐pitch interconnects. Conventional ACAs require relatively high bonding pressures and temperatures, and ultra fine‐pitch applications challenge the trade‐off between low interconnect resistance and risk of short circuits. This study introduces an ACA‐like interconnection technology that addresses these limitations, allowing for low‐pressure, low‐temperature assembly processes with enhanced particle control at the interconnects. Conductive particles are deposited onto a patterned carrier and subsequently transferred to electrical pads using either non‐conductive film or Ag sintering. The Ag sintering process is performed at a low temperature (140 °C) and low bonding pressure (1 N for a 10 × 10 mm2 chip). The capability of controlling the position and number of conductive particles within individual interconnects is demonstrated. This presents possibilities for achieving ultra‐fine pitch interconnects with negligible risk of short circuits, without compromising electrical resistance. It is demonstrated that interconnect resistance can be tuned by varying the number of conductive particles (achieving a resistance as low as 33 mΩ with 25 particles per interconnect). This approach is applicable to scenarios where the bonding force and temperature must remain low due to the nature of substrate materials.

Flip-Chip Interconnects Based on Single Metal-Coated Polymer Spheres

In microelectronics packaging, minimizing thermomechanical stresses is crucial to achieve high reliability. This paper presents a novel approach for flip-chip interconnects, utilizing individual metal-coated polymer spheres at a low bonding temperature. The method involves selectively depositing individual conductive particles onto a polydimethylsiloxane (PDMS) carrier and then transferring the particles to electrical pads on substrate using Ag sintering followed by die placement and introducing underfill material. The deposition process achieved a high yield of 98.8% on the PDMS carrier, while the transferring process resulted in well-defined ink dots with a yield of 96.2%. The sintered Ag formed good bonds between the particles and electrical pads, leading to moderate interconnect resistance (as low as 0.57 Ω). This work has demonstrated the feasibility of interconnects based on a single metal-coated polymer sphere with low thermomechanical stress induced, thanks to the low bonding temperature (140 °C) and pressure (0.1 MPa) as well as the mechanical compliance of polymer particles.

Structure and impedance of TiN coated 304L SS substrates

In the present work, the effect of the deposition time on the structure and electrical impedance of reactive DC magnetron sputtered TiN coatings was studied. The structure of the coatings and the substrates was studied using X-ray diffraction (XRD). The electrical impedance and high frequency stability of the specimens was experimentally measured and the results were indicative of whether the application of the coatings as protective layers between the electrical contact pads of electrical contact systems is feasible.

A Flow Sensing Device Formed Exclusively by Employing Additive Manufacturing for On-Site Fabrication Aboard a Ship.

This work concerns the design, fabrication, and testing of a novel air-flow sensor employing exclusively additive manufacturing that can be fabricated on-site, aboard a ship, or in a similarly remote area, without relying on external manufacturing facilities. The developed device's principle of operation is based on vortex shedding; its novelty focuses on employing solely additive manufacturing technology, for the manufacturing-in a single process step-of all the sensor's main elements. In more detail, the required flow-shaping housing, the appropriate piezoresistive sensing element, and the electrical interconnection pads are all constructed in a single process step, through standard Fused Deposition Modeling (FDM) 3D technology. Direct communication to the necessary readout circuitry can be easily achieved through standard soldering utilizing the integrated contact pads of the sensor. The prototype was preliminary characterized, validating its proper functionality. Key features of the proposed device are low cost, fast on-site manufacturing of the entire measuring device, robustness, and simplicity, suggesting numerous potential applications in the shipbuilding industry and other industrial sectors.

Electrically reconfigurable waveguide Bragg grating filters.

We propose and demonstrate an electrically reconfigurable waveguide Bragg grating filters in silicon-on-insulator using a multiple-contact heater element. There are six electrical pads connected to the heater element in an equidistant manner. These electrical pads allow to create different heat, and corresponding refractive index, distributions across the grating so that the local Bragg wavelength corresponding to the heated segments can be controlled. In turn, this control over the heat distribution allows the device to be reconfigured to implement different filter spectral responses. These filters are applicable for both wavelength division multiplexing systems and optical signal processing applications. As a verification, we demonstrate the generation of two (or more) separate filter bands with a spacing up to 35 nm or a Fabry-Pérot cavity with a 1.6 nm free-spectral range. Moreover, we explain a firm and accurate simulation framework of the proposed device based on COMSOL Multiphysics and the transfer matrix method, which is in excellent agreement with our experimental measurements.

Compact Wavelength Selective Crossbar Switch with Cascaded First Order Micro-Ring Resonators

We demonstrate a compact 4×4 wavelength selective switch with 50% fewer electrical signal pads as compared with our previous generation. We report loss and crosstalk for different paths of the switch. We measure median loss of 5.32 dB and worst case crosstalk of −35 dB. The microring resonators tune by more than one free spectral range, which is an improvement over our previous generation of switches. This switch can support 8 channels at 400 GHz spacing. We conclude that it is possible to drive both microring resonators with the same voltage and separate control is not required if the fabrication variation reduces in the future.

Wafer-level hermetically sealed silicon photonic MEMS

The emerging fields of silicon (Si) photonic micro–electromechanical systems (MEMS) and optomechanics enable a wide range of novel high-performance photonic devices with ultra-low power consumption, such as integrated optical MEMS phase shifters, tunable couplers, switches, and optomechanical resonators. In contrast to conventional SiO 2 -clad Si photonics, photonic MEMS and optomechanics have suspended and movable parts that need to be protected from environmental influence and contamination during operation. Wafer-level hermetic sealing can be a cost-efficient solution, but Si photonic MEMS that are hermetically sealed inside cavities with optical and electrical feedthroughs have not been demonstrated to date, to our knowledge. Here, we demonstrate wafer-level vacuum sealing of Si photonic MEMS inside cavities with ultra-thin caps featuring optical and electrical feedthroughs that connect the photonic MEMS on the inside to optical grating couplers and electrical bond pads on the outside. We used Si photonic MEMS devices built on foundry wafers from the iSiPP50G Si photonics platform of IMEC, Belgium. Vacuum confinement inside the sealed cavities was confirmed by an observed increase of the cutoff frequency of the electro-mechanical response of the encapsulated photonic MEMS phase shifters, due to reduction of air damping. The sealing caps are extremely thin, have a small footprint, and are compatible with subsequent flip-chip bonding onto interposers or printed circuit boards. Thus, our approach for sealing of integrated Si photonic MEMS clears a significant hurdle for their application in high-performance Si photonic circuits.

Laser-Induced Period Surface Structures to Improve Solderability of Electrical Solder Pads

We report on structuring copper representing soldering pads of printed circuit boards by laser-induced periodic surface structures. Femtosecond laser radiation is used to generate low spatial frequency laser-induced surface structures, having a spatial period of 992 nm and a modulation depth of 120 nm, respectively. The slump of screen-printed solder paste is measured to compare the solder coverage on the pads after the solder process on a hot plate. A comparative study of the coverage of solder paste on a fresh polished pad, a pad stored for two weeks, and femtosecond laser-structured pads reveals the improved wettability of structured pads even after storage. In addition, leaded and lead-free solder pads are compared with the particular advantages of the solder-free pad when periodically laser structured. Our findings are attributed to two major effects: namely, the increase of the surface area and the improved surface chemical wettability. Overall, the application of laser-induced periodic surface structures helps to reduce the demand of lead-based solder in the electronic industry and provides a feasible method for a fast and spatial selective way of surface functionalization.

Formation of Efficient Microfilm Converters with Reproducible Parameters

The use of microfilm converters provides information in the field of processing, storage, transmission and presentation of information, especially in the process of control and measurement of physical quantities, as well as in the technology of manufacturing high technology products. Microfilm transducers form an equivalent output signal, which is a function of the measured quantity; their design and manufacturing technology are interrelated and highly correlated. Microfilm transducers are manufactured using microelectronic technology, in which group methods are used in the formation of a structure, which increases the reproducibility of parameters, are characterized by high sensitivity, low inertia, low power consumption, high reliability, and are combined with measuring signal processing devices. When creating microfilm converters, a structure is determined that most closely meets the requirements, design parameters, modes of manufacturing operations, the effect of operating conditions on characteristics, and optimal modes of operation. Structurally, a microfilm transducer consists of a base, an insulated structure, heat-generating and temperature-sensitive elements that provide the transmission of electrical signals, film conductors and contact pads, which provide a specified function of converting the measured value into an output signal. In microfilm converters, film thermocouples are used as thermosensitive elements, and adhesive sublayers are used in their manufacturing technology. The use of technological methods of microelectronics when creating microfilm converters can significantly improve their operational parameters.

Characterization of a Micro Beam Fabricated with 3D Technology Using Image Processing Algorithm

Background:: This article presents a micro beam, fabricated using digital light processing (DLP), one of the additive manufacturing methods. The fabrication process is based on the projection micro stereolithography method. Objective:: The micro beam, which can move in one direction (y-axis), was designed according to the specified criteria and fabricated. In the experiments carried out during the fabrication process, it showed the effect of the support structures on the fabrication of the micro beam. Methods:: For the characterization process, the micro beam connected to the probe station is connected to a circuit board with cables attached to the electrical pads. The image processing algorithm has been developed to detect the displacement of the micro beam as a result of the characterization processes. The operating voltage was increased from 0V to 2V and incremented until fracture and deterioration in the structure of the micro beam were observed. Results:: The micro beam was able to withstand distortion and breaks up to a maximum voltage of 10V. When 12V voltage was applied to the micro beam, fractures occurred in the arm. As a result of the characterization process, the maximum displacement of the micro beam was measured as 2.32 μm at 10V voltage. Conclusion:: The characterization results indicated the usability of the image processing algorithm in 3D technology.

Self-adaptively inpainting gaps between electrical image pads according to the image fabric

Self-adaptively inpainting gaps between electrical image pads according to the image fabric

A Wavelength-Selective Multiwavelength Ring-Assisted Mach–Zehnder Interferometer Switch

Wavelength-selective switches have been proposed for datacenter use to enhance the scalability of their networks to help in meeting ever-increasing traffic demands. We have previously demonstrated a 4 × 4 ring-based crossbar silicon photonic switch in which each cross-point contained three ring pairs to partition the free spectral range (FSR) into three equal regions to reduce wavelength tuning range per ring pair—thereby reducing both the tuning power consumption and stress on the rings—while maintaining full routing flexibility. However, the question of scalability remains for such a crossbar switch in which 96 signal pads—one routed to each ring—are required to fully control it. In this article we present a 4-port silicon photonic ring-assisted Mach–Zehnder interferometer (RAMZI) switch with multiple-sized rings per switching elements in a Benes network configuration to reduce the number of electrical pads required to 36 signal pads for the equivalent number of wavelength-selective switch elements per switch cell. The switch is 500 μm × 3 mm in size and is packaged on a custom PCB. Another advantage the RAMZI switch has over the crossbar switch is that the loss through the switch is not path-dependent due to its balanced path configuration. In the crossbar switch, the difference between the shortest and longest paths is 2(N − 1) switching elements. Finally, we present results from the fabricated switch and the outlook for further scaling of the switch architecture.

Monolithic integration of MEMS thermal flow sensor and its driving circuit onto flexible Cu on polyimide film

A thermal sensor integrated with its driving circuit by using Cu on polyimide (COP) as a substrate was developed. A heater, working as the thermal flow sensor and constant temperature circuit (CTC), working as its driving feedback circuit, were successfully integrated on the COP substrate by photolithography, metal deposition, and sacrificial selective etching in the Cu layer. The Cu layer works to form a cavity that acts thermal isolation for the heater and electrical feedthroughs in the CTC. The electrical components, i.e., resistors, capacitors, and operational amplifiers, were mounted on the electrical pads using low-temperature solder paste of Sn–Bi at the CTC area. The areas of the thermal sensor and CTC were 11 × 23 mm and 16 × 24 mm, respectively. The area of the thermal sensor was inserted into a tube with a diameter of 5 mm acting as the flow sensor. The sensor outputs increased along with the airflow rate up to 10.0 L/min, and the calibration curve as the airflow-rate sensor was experimentally derived. The fabricated sensor outputs were not affected by variations in the airflow temperature and only depended on the airflow rate thanks to the added temperature compensation function, and a response time of 0.095 s was obtained.

Study of K-Nearest Neighbour Classification Performance on Fatigue and Non-Fatigue EMG Signal Features

For our body to move, the muscle must activate by relaxing and contracting. Muscle activation produces bio-electric signals that can be detected using Electromyography or EMG. The signal produced by the muscle is affected by the type of contraction done by the muscle. The eccentric contraction generating different EMG signals from concentric contraction. EMG signal contains multiple features. These features can be extracted using MATLAB software. This paper focuses on the bicep brachii and brachioradialis in the upper arm and forearm, respectively. The EMG signals are extracted using surface EMG whereby electrical pads are placed onto the surface of the muscle. Features can then be extracted from the EMG signal. This paper will focus on the MAV, VAR, and RMS features of the EMG signal. The features are then classified into eccentric, concentric or isometric contraction. The performance of the K-Nearest Neighbour (KNN) classifier is inconsistent due to the EMG data variabilities. The accuracy varies from one data set to another. However, it is concluded that non-fatigue signal classification accuracy is higher than fatigue signal classification accuracy.

In-Space Manufacturing of Carbon Nanotube Biosensor for Crew Health Diagnostics

The impact of space environment in human physiology is one of the biggest hurdles for the success of long duration manned missions.1 Traditionally, the impact of space environment is assessed by comparing different physiological parameters before and after deployment. For long duration missions (i.e Moon or Mars), sample return for a ground base analysis will be impractical and in-flight, portable analytical devices will be required. Additionally, the further crew travel from earth, the less feasible it is to rely on resupply of these portable analytical devices. One solution is to develop methodologies for manufacturing analytical devices on-demand and in an in-space environment. Electrochemical biosensors can serve as point-of-care (POC) analytical devices as they can be easily fabricated onto cheap, disposable substrates by printing nanomaterial-based electronic inks. Inkjet printing is a suitable deposition technique as it provides contactless deposition of material droplets (ink) in very precise coordinates (high spatial resolution), allowing the fabrication of complex features.2 This offers a highly tailorable manufacturing process as the printed features are based on a easily adjustable/editable digital file. Also, this manufacture approach is amenable for an in-space environment fabrication due to its low dependence on an operator, fast manufacturing time with low waste generation, easily scalable, highly/easily tunable, ability to print a variety of electronic inks (conductors and insulators) with minimal chance of cross contamination between materials and different types of sensors can be manufactured using the same printer.3,4 Inkjet printing has the added advantage of allowing POC devices to be manufacture on a demand basis, optimizing resource use. Here we present the first steps of the development of a print-on-demand 3-electrode electrochemical biosensor for the detection of cortisol, a stress biomarker.5 For these devices, 3 types of inks were use: multi walled carbon nanotubes (MWCNT), silver nanoparticles (AgNP) and SU-8. First, AgNP ink was printed onto a kapton substrate to define the reference electrode (RE), electrical contact pads and electrical connections. Second, MWCNT ink was printed to generate the working electrode (WE) and the counter electrode (CE). Third, the SU-8 ink is used to encapsulate and insulate the AgNP electrical connectors. Lastly, the surface of the WE was modified with an antibody anti-cortisol using EDC/NHS coupling chemistry. The surface modification and detection of cortisol is identified through a measurable electrical change such as current and impedance, etc.6 (1) Demontis, G. C.; Germani, M. M.; Caiani, E. G.; Barravecchia, I.; Passino, C.; Angeloni, D. Human Pathophysiological Adaptations to the Space Environment. Front. Physiol. 2017, 8, 1–17. (2) Raut, N. C.; Al-Shamery, K. Inkjet Printing Metals on Flexible Materials for Plastic and Paper Electronics. J. Mater. Chem. C 2018, 6 (7), 1618–1641. (3) Li, J.; Rossignol, F.; Macdonald, J. Inkjet Printing for Biosensor Fabrication: Combining Chemistry and Technology for Advanced Manufacturing. Lab Chip 2015, 15 (12), 2538–2558. (4) Khan, S.; Ali, S.; Bermak, A. Recent Developments in Printing Flexible and Wearable Sensing Electronics for Healthcare Applications. Sensors (Basel). 2019, 19 (5). (5) Hellhammer, D. H.; Wüst, S.; Kudielka, B. M. Salivary Cortisol as a Biomarker in Stress Research. Psychoneuroendocrinology 2009, 34 (2), 163–171. (6) Kimmel, D. W.; LeBlanc, G.; Meschievitz, M. E.; Cliffel, D. E. Electrochemical Sensors and Biosensors. Anal. Chem. 2012, 84, 685–707.

Metal–interlayer–metal structured initiator containing Al/CuO reactive multilayer films that exhibits improved ignition properties

Aluminum/cupric oxide (Al/CuO) reactive multilayer films (RMFs) are widely used for micro-chip energetic initiator applications; however, there are only a few examples where they are initiated through the direct input of electrical energy. This study describes the preparation of micro-chip energetic initiators containing Al/CuO RMFs as an interlayer between two Al electrical contact pads that are prepared using an image reversal lift-off process and the magnetron sputtering technology. This design enables the direct transfer of current from the contact pads to Al/CuO RMFs, which results in fast ignition (less than 1.0 μs) and produces luminous flame ball that spread over a wide area (maximum flame area of 13.8 mm2). A metal–interlayer–metal (MIM) structured initiator will not be fired until the external voltage has exceeded the breakdown field strength of CuO layers. These initiators achieved a critical breakdown voltage (VB) of 32–50 V and a complete electrical-explosion voltage (VC) of 72–84 V. The ignition threshold rises with increasing the bilayer thicknesses of the RMFs. These characteristics of this specially structured initiator are well suited for applications in highly efficient and insensitive initiating explosive devices.

Development, Modeling, Fabrication, and Characterization of a Magnetic, Micro-Spring-Suspended System for the Safe Electrical Interconnection of Neural Implants.

The development of innovative tools for neuroscientific research is based on in vivo tests typically applied to small animals. Most often, the interfacing of neural probes relies on commercially available connector systems which are difficult to handle during connection, particularly when freely behaving animals are involved. Furthermore, the connectors often exert high mechanical forces during plugging and unplugging, potentially damaging the fragile bone structure. In order to facilitate connector usage and increase the safety of laboratory animals, we developed a new magnetic connector system circumventing the drawbacks of existing tools. The connector system uses multiple magnet pairs and spring-suspended electrical contact pads realized using micro-electromechanical systems (MEMS) technologies. While the contact pad suspension increases the system tolerance in view of geometrical variations, we achieved a reliable self-alignment of the connector parts at ±50 µm provided by the specifically oriented magnet pairs and without the need of alignment pins. While connection forces are negligible, we can adjust the forces during connector release by modifying the magnet distance. With the connector test structures developed here, we achieved an electrical connection yield of 100%. Based on these findings, we expect that in vivo experiments with freely behaving animals will be facilitated with improved animal safety.