Showing papers in "IEEE Transactions on Components, Packaging and Manufacturing Technology in 2018"

Design and Packaging of an Eye-Shaped Multiple-Input–Multiple-Output Antenna With High Isolation for Wireless UWB Applications

Abstract: This paper presents a bandwidth enhanced, compact, multiple-input–multiple-output (MIMO) antenna with high isolation for modern wireless ultrawideband (UWB) applications. The proposed antenna consists of two simple eye-shaped slot radiators, and in order to enhance isolation, the proposed antenna uses a rectangular-shaped ground plane with an extruded T-shaped stub. The antenna characteristics such as the S-parameters, realized gain, surface current distributions, and radiation patterns are investigated. Furthermore, the diversity performance of MIMO antenna in terms of envelope correlation coefficient (ECC), diversity gain (DG), total active reflection coefficient (TARC), and multiplexing efficiency is also studied. The designed antenna shows the impedance bandwidth of 17.2 GHz (from 2.8 to 20 GHz) with a compact size of $18\times 36$ mm2. The antenna possesses a low mutual coupling of less than −20 dB over the operating band, the ECC and the DG are less than 0.02 and greater than 9.95 dB, respectively. The prototype is fabricated and tested for impedance and radiation characteristics. The proposed antenna when installed on a printed circuit board with a standard size, with USB connector, and device housing and various other types of housing show good performance. The proposed MIMO/diversity antenna can be a good candidate for portable UWB applications.

An sEMG-Based Human–Robot Interface for Robotic Hands Using Machine Learning and Synergies

Abstract: Developing natural control strategies represents an intriguing challenge in the design of human–robot interface (HRI) systems. The teleoperation of robotic grasping devices, especially in industrial, rescue, and aerospace applications, is mostly based on nonintuitive approaches, such as remote controllers. On the other hand, recent research efforts target solutions that mimic the human ability to manage multifinger grasps and finely modulate grasp impedance. Since electromyography (EMG) contains information about human motion control, it is possible to leverage such neuromuscular knowledge to teleoperate robotic hands for grasping tasks. In this paper, we present an HRI system based on eight fully differential EMG sensors connected to a wearable sensor node for acquisition and processing. By virtue of a novel bio-inspired approach, the embedded myocontroller merges pattern recognition and factorization techniques to combine a natural selection of the robotic hand configuration with the proportional control of the related grasps. The HRI system has been fully designed, implemented, and tested on two robotic hands: a dexterous anthropomorphic hand and a three-fingered industrial gripper mounted on a robotic manipulator. The results of the test performed on four able-bodied subjects show success rates greater than 90% reached in grasping objects that require different hand shapes and impedance regulations for the task completion. The outcomes also show that the users modulate the bio-inspired degrees of control in a natural manner, proving the pertinence of the proposed system for an effective human-like control of robotic grasping devices in a wearable form factor.

Wire Defect Recognition of Spring-Wire Socket Using Multitask Convolutional Neural Networks

Abstract: As a critical electrical connector component in the modern industrial environment, spring-wire sockets and their manufacture quality are closely relevant to equipment safety. These types of defects in a component are difficult to properly distinguish due to the defect similarity and diversity. In such cases, defect types can only be determined using cumbersome human visual inspection. To satisfy the requirements of quality control, a machine vision apparatus for component inspection is presented in this paper. With a brief description of the apparatus system design, our emphasis is put on the defect recognition algorithm. A multitask convolutional neural network (CNN) is proposed for detecting those ambiguous defects. Compared with the image processing method in machine vision, the defect inspection problem is converted into object detection and classification problems. Instead of breaking it down into two separate tasks, we jointly handle both aspects in a single CNN. In addition, data augmentation methods are discussed to analyze their effects on defects recognition. Successful inspection results using the presented model are obtained using challenging real-world defect image data gathered from a spring-wire socket module inspection line in an industrial plant.

Design, Materials, Process, Fabrication, and Reliability of Fan-Out Wafer-Level Packaging

Abstract: The design, materials, process, fabrication, and reliability of fan-out wafer-level packaging (FOWLP) with chip-first and die face-up method are investigated in this paper. Emphasis is placed on the issues and their solutions (such as reconstituted carrier, die-attach film placement, pitch compensation, die shift, epoxy molding compound dispensing, compression molding, warpage, and Cu revealing) during the fabrication of a very large test chip (10 mm $\times10$ mm $\times 150\,\,\mu \text{m}$ ) and test package (13.47 mm $\times13.47$ mm), and three redistribution layers with the smallest linewidth/spacing = $5~\mu \text{m}/5~\mu \text{m}$ . The FOWLP test package on a six-layer printed circuit board is subjected to 1000 drops of the shock test with a magnitude = 1500 G/ms. Recommendations of process integration and guidelines on FOWLP with chip-first and die face-up are provided.

SMT Solder Joint Inspection via a Novel Cascaded Convolutional Neural Network

Abstract: Due to the excellent self-learning ability of deep learning, we propose a novel deep-learning-based method to inspect surface-mount technology (SMT) solder joints in this paper. In contrast to the state-of-the-art learning-based methods in which low-level features are extracted before learning, our method directly implements the inspection task without low-level feature extraction, which is based on a novel cascaded convolutional neural network (CNN). Three kinds of CNNs with different network parameters compose the proposed cascaded CNN. First, one kind of CNN is employed to adaptively learn the regions of interest (ROIs) of SMT solder joint images. Then, both the learned ROIs and the entire solder joint images are fed into the other two kinds of CNNs, respectively. Finally, inspection results are achieved by the learned cascaded CNN. Comparison experiments indicate that our proposed method can achieve more excellent inspection performance for SMT solder joints than that of the state-of-the-art methods.

Inkjet Printing of Wideband Stacked Microstrip Patch Array Antenna on Ultrathin Flexible Substrates

Abstract: This paper presents a bandwidth-enhanced, low-cost, compact, inkjet-printed multilayer microstrip fractal patch antenna for integration into flexible and conformal devices. The antenna consists of two layers of patches, with the first layer inkjet-printed directly on a 0.125-mm (only 0.005 of the operating wavelength) Kapton polyimide substrate. On top of it, a 0.12-mm-thick SU-8 polymer is covered. To achieve the desired miniaturization and good impedance match, a Minkowski fractal geometry patch is employed as the second layer inkjet-printed on top of the SU-8 polymer. The proposed antenna has compact dimensions of only $22\times 31$ mm2 and covers 4.79–5.04-GHz frequency spectrum with $S_{11} dB. Moreover, a 2-bit $1\times 4$ phased array antenna (PAA) is constructed, and its scan ability is estimated to demonstrate its potential application in the true-time-delay flexible PAA systems. The prototype is fabricated and tested for impedance and radiation characteristics. The measured and the simulation results show the superiority of the proposed antenna.

Fan-Out Wafer-Level Packaging for Heterogeneous Integration

Abstract: The design, materials, process, fabrication, and reliability of a heterogeneous integration of four chips and four capacitors by a fan-out wafer-level packaging (FOWLP) method are investigated in this paper. Emphasis is placed on the application of a new assembly process for fabricating the redistribution layers of the FOWLP. Reliability assessments, such as the thermal cycling and drop test, are also performed.

A Scalable and Multidirectional Rectenna System for RF Energy Harvesting

Abstract: A rectenna system having multidirectional receiving capability and scalable antenna gain is presented for radio frequency (RF) energy harvesting. The technique of ray tracing was implemented to evaluate RF power collected by antennas with different half-power beam widths. The results indicate that different radiation features are suited to distinct scenarios. This further indicates that a scalable and multidirectional radiation characteristic is highly desired for energy-harvesting antennas because the level of ambient energy varies over time and space. Accordingly, a rectenna system is proposed that can scale in array size, antenna gain, direction of reception, and radiation pattern to enhance conversion efficiency and dc outputs. The proposed device is comprised of five rectenna cells. Each cell consists of a quasi-Yagi antenna with variable numbers of directors and one RF-to-dc energy-harvesting circuit. Thus, the proposed system can achieve either uniform coverage with enhanced antenna gain or highly directional characteristics at one/multiple incidence angle(s). A prototype is designed, fabricated, and tested in terms of each component and the entire system. The experimental results indicate that the proposed system can be useful in various scenarios, and it outputs enhanced power as scaling is performed in the direction of reception and antenna gain.

Independently Tunable/Controllable Differential Dual-Band Bandpass Filters Using Element-Loaded Stepped-Impedance Resonators

Abstract: This paper presents a new approach for designing differential bandpass filter (BPF) with independently tunable/controllable dual passbands using the element-loaded stepped-impedance resonators (SIRs). The frequency-agile ability of the fundamental and third-harmonic resonant frequencies ( $f_{1}$ and $f_{3})$ of the element-loaded SIR against the value of the loaded element under different loading positions on the SIR is theoretically analyzed. It can be found that there must be a position that could be utilized to load element to realize the independent control of $f_{1}$ without affecting $f_{3}$ . This feature is successfully applicable to design independently tunable differential dual-band BPF when the loaded elements are tunable capacitors. Furthermore, by making the loaded elements to be shunt stubs, a new coupling path can be constructed for $f_{1}$ , and then the coupling coefficients for the two bands can be separately varied. Both the operational frequencies and bandwidths of the two bands can be separately adjusted. As a result, the traditional design procedure for the differential dual-band BPF can be simplified significantly. For demonstration, two examples are designed, implemented, and measured, and their simulation and measured results are presented, showing good accordance.

Substrate-Integrated Waveguide Dual-Band Filters With Closely Spaced Passbands and Flexibly Allocated Bandwidths

Abstract: Substrate-integrated waveguide (SIW) dual-band bandpass filters (BPFs) with closely spaced passbands and flexibly allocated bandwidths are presented based on TE102 and TE201 modes in substrate-integrated rectangular cavities (SIRCs). The constraint relationship among the first four mode resonances in an SIRC with its aspect ratio is theoretically analyzed first to explore the realizable frequency ratio of TE102 and TE201 modes. The fractional bandwidth (FBW) design graphs are also delineated to demonstrate the available FBWs of the two passbands. Two SIW dual-band BPFs, including a third-order direct-coupled one centered at 20 and 22 GHz with respective FBWs of 2.6% and 3.9%, and a fourth-order cross-coupled one centered at 20 and 21.5 GHz with both FBWs of 2.35%, are designed, fabricated, and tested for demonstration, showing good agreement between the simulation and measured results.

Machine-Learning Approach in Detection and Classification for Defects in TSV-Based 3-D IC

Abstract: A through-silicon via (TSV) is a conducting copper nail, which provides an electrical connection through a substrate, and is expected to be used extensively to provide high-speed interconnects between the top and bottom of an active die. However, some TSV structural defects such as pinholes and voids are difficult to capture as they commonly affect TSV performance parameters rather than TSV logical function. In order to electrically detect failures, it is necessary to study and analyze electrical characteristics of defects in advance. Testing TSV interconnects for manufacturing defects poses major challenges, and new design-for-test techniques are needed. Here, a novel nondestructive defect detection method using machine learning (ML) is proposed in order to detect void, short, and open defects in TSV-based 3-D ICs. A supervised ML approach is used to build a classification model from training S-parameter data sets containing the defected TSV and the normal TSV. The performance of the random forest classifier is tested for various amounts of void, short, and open defects in TSV-based 3-D-stacked ICs with satisfactory results.

Packaging Solution for a Millimeter-Wave System-on-Chip Radar

Abstract: In this paper, a packaging solution for millimeter-wave system-on-chip (SoC) radio transceivers is presented. The on-chip antennas are realized as primary radiators of an integrated lens antenna which offer high bandwidth and high efficiency. The package concept includes a high permittivity silicon lens which serves additionally as heat sink and a quad flat no-lead package which is mountable on a standard printed circuit board (PCB). The electrical and thermal properties of the package are investigated through simulations and calibrated measurements. The concept is verified by realizing a complete radar sensor. The manufactured SoC radar frontend is soldered on a standard PCB which includes the baseband circuitry for a frequency-modulated continuous wave radar and finally, measurements are performed to compare the superposed radiation patterns of the transmit and receive antennas with simulations.

FPGA-Based Embedded Cyber-Physical Platform to Assess Gait and Postural Stability in Parkinson’s Disease

Abstract: Abnormal gait and postural instability are common disorders in people affected by Parkinson’s disease (PD). This paper proposes an embedded cyber-physical system for the identification and the real-time extraction of highly selective diagnostic indexes for PD patients. A noninvasive wearable and wireless architecture for both gait analysis and postural instability detection has been proposed and implemented on a programmable hardware. The combined analysis of electroencephalography and electromyography allows studying the motor cortex activity through the movement-related potentials, determining a novel set of indexes that could be used for the PD diagnosis and classification. In a future perspective of an application-specific integrated circuit implementation, the real-time data processing has been fully realized on the Altera Cyclone V field-programmable gate array (FPGA), without interactions with embedded processor architecture. Referring to an Altera Cyclone V SE 5CSEMA5F31C6N device, the whole implemented architecture exploits 90% of the available FPGA adaptive logic modules, 74% of the manageable registers, and 10.3% of the total memory, as well as 29.7% wires utilization. Furthermore, the system is able to provide the outputs in about 57 ms with a dynamically power dissipation of 89 mW. The platform has been tested in vivo on two Parkinson’s patients and two healthy subjects (control group) covering three typical diagnostic scenarios: PD versus controls, drug treatment evaluation, and involuntary movements detection.

Chip-First Fan-Out Panel-Level Packaging for Heterogeneous Integration

Abstract: The design, materials, process, fabrication, and reliability of a heterogeneous integration of four chips by a fan-out panel-level packaging (FOPLP) method are investigated in this paper Emphasis is placed on the application of a special assembly process called uni-substrate-integrated package for fabricating the redistribution layers (RDLs) of the FOPLP The Ajinomoto build-up film is used as the dielectric of the RDLs and is built up by the semiadditive process The electroless Cu is used to make the seed layer, the laser direct imaging is used for opening the photoresist, and the printed circuit board Cu plating is used for making the conductor wiring of the RDLs Reliability assessments such as the drop test and thermal cycling test are also performed

Effects of Voids on Mechanical and Thermal Properties of the Die Attach Solder Layer Used in High-Power LED Chip-Scale Packages

Abstract: High-power light-emitting diode (LED) chip-scale packages (CSPs) prepared by the flip-chip technology have become one of the most promising light sources. The die attach solder layer always plays an important role in heat dissipation, mechanical support, and electronic conductivity. Among different types of solder materials, Sn-3.0Ag-0.5Cu (SAC305) solder alloy shows its great competitiveness on solderability and mechanical properties for the interconnection of high-power LED CSPs. However, reliability problems caused by voids in the SAC305 solder limit its wide application in the high-power LED chip-scale packaging process. Existence of the voids has been considered as one of the major issues causing chip-on-substrate level reliability problems in microelectronic and optoelectronic devices. In this paper, mechanical and thermal properties of SAC305 solder layers with arbitrary voids used in high-power LED CSPs are studied with both finite-element simulations and experiments. The results show that void size and void position within the solder layer are the two most critical issues on the shear strength of interconnection and the chip-on-substrate level thermal distribution in high-power LED CSPs.

Effect of Cycling Amplitude Variations on SnAgCu Solder Joint Fatigue Life

Abstract: Reliability of conventional electronic assemblies in real service applications is typically limited by fatigue failure of a single solder joint in reversed cyclic loading. Fatigue damage accumulation in a lead-free solder joint is still not well understood, especially not for cycling with a varying amplitude; i.e., random vibration testing is not representative of realistic service conditions and the common reliability models fail to offer relatively accurate life predictions. Developing or modifying a fatigue life model should, of course, consider the interactive effect of stress amplitude variations, which is found to be substantial. Cycling real individual SnAgCu solder joints with systematically varying stress amplitudes allowed understanding of the fatigue damage accumulation through monitoring of the plastic work dissipation during cycling. The results show a significant amplification in the work dissipation compared to what was expected based on fixed stress amplitude cycling results. Cycling with combinations of 16- and 20-MPa stress amplitudes leads to amplification of the work (more fatigue damage) at the 16-MPa amplitude, but no significant change in damage accumulation at the 20-MPa amplitude. Cycling with combinations of three or more stress amplitudes leads to work amplification at the lowest amplitude, no change at the higher amplitude, and slight to moderate amplifications at the intermediate amplitudes. In addition, the value of the work amplification at any stress amplitude depends on the sequence of higher amplitudes applied immediately before it. It is also found that any high amplitude does not affect subsequent work at a lower amplitude if an even higher amplitude was applied just before it.

Signal Integrity Design and Analysis of Silicon Interposer for GPU-Memory Channels in High-Bandwidth Memory Interface

Abstract: In this paper, for the first time, we designed and analyzed channels between a graphic processing unit and memory in a silicon interposer for a 3-D stacked high bandwidth memory (HBM). We thoroughly analyzed and verified the electrical characteristics of the silicon interposer considering various design parameters, such as the channel width and space, redistribution layer via, and under bump metallurgy pads. In particular, we also considered the meshed ground planes used for the proposed transmission lines, which are microstrip and strip lines. Signal integrity (SI) of the proposed channels in the silicon interposer was successfully analyzed and verified using a full 3-D electromagnetic solver and circuit simulations. Based on the extracted lumped circuit resistance, inductance, conductance and capacitance parameters, we thoroughly analyzed the channel characteristics and identified the parameters that dominantly affect SI in relation to each frequency range. From the analyzed insertion loss and far end crosstalk, we verified SI of the silicon interposer by eye-diagram simulations in terms of eye-height voltage and timing jitter in the time domain. In the worst case, the eye-height voltage and timing jitter of the proposed microstrip lines are 0.911 V and 36.8 ps, respectively, with 72 mV of signal coupling. The eye-height voltage and timing jitter of the proposed strip line are 0.887 V and 42.1 ps with 34 mV of single couplings. We show that the proposed channels of the silicon interposer can successfully transfer data at a 2-Gb/s data rate. Finally, we propose concepts and solutions for the next-generation HBM interface with higher data rates up to 8 Gb/s.

Warpage Measurements and Characterizations of Fan-Out Wafer-Level Packaging With Large Chips and Multiple Redistributed Layers

Abstract: In this paper, the warpages of a chip-first and die face-up fan-out wafer-level packaging (FOWLP) with a very large silicon chip (10 mm $\times \,\, 10$ mm $\times \,\, 0.15$ mm) and three redistributed layers are measured and characterized. Emphasis is placed on the measurement and 3-D finite-element simulation of the warpages during the FOWLP fabrication processes, especially for: 1) right after postmold cure; 2) right after backgrinding of the epoxy molding compound to expose the Cu-contact pads; and 3) the individual package (right after the solder ball mounting and dicing) versus surface mount technology reflow temperatures. The simulation results are compared to the measurement results. Some recommendations on controlling the warpages are provided.

3-D Printing of Conformal Antennas for Diversity Wrist Worn Applications

Abstract: This paper presents for the first time the application of 3-D printing techniques for the development of conformal antennas for diversity wrist worn wireless communications. Three processes are described with the common challenge of depositing the metallic layers of the antennas on a bracelet fabricated using fuse filament fabrication. The first is a multistep process that combines adding a layer to smooth the surface of the band, aerosol jetting the metallic tracks, flash curing, and then electroplating. The second combines painting the metallic layers by hand and then electroplating. The last process uses a single machine to fabricate both the bracelet and then the metallic layers by means of a direct write system with silver conductive ink. The wrist worn antennas are presented and its performances on the human wrist are discussed. All antennas cover 2.4 and 5.5 GHz used for WLAN communication with the reflection coefficients less than −10 dB. The diversity wrist worn antennas system is developed for the final two processes. Three WLAN antennas are fabricated at different positions and shape angles within the bracelet. In terms of communications systems, the advantage of this configuration is that it can increase coverage. The radiation patterns of the antenna are nearly omnidirectional in free space and directional on the human wrist. When the patterns of the three antennas are combined together, the coverage for the communication system improves. Simulation results of all antenna designs and studies using the finite integration technique agree well with experimental measurement results. The main motivation of this paper is to investigate alternative additive manufacturing methods for the development of conformal diversity antennas on customized 3-D printed parts.

Dynamic Performance of Electrical Connector Contact Resistance and Intermittent Fault Under Vibration

Abstract: Static electrical contact resistance (ECR) has been well researched. To investigate the dynamic performance of electrical connector under vibration, a test apparatus is built to measure the ECR with high precision. The ECRs are tiny and suffer from noise. Therefore, a wavelet packet transform-based denoising method is proposed. This method can filter noise with frequency components ranging from low to high. The dynamic characteristics of ECR are presented after an analysis of the measured results. Moreover, the connector intermittent fault (IF) performance under vibration is characterized and analyzed. Finally, an ECR model for rough surfaces under vibration is proposed, based on which the discovered laws are theoretically analyzed. The detected dynamic characteristic of ECR and IF can support an online diagnosis of connectors in further research.

Electrical Modeling and Characterization of Silicon-Core Coaxial Through-Silicon Vias in 3-D Integration

Abstract: Based on the extracted resistance, inductance, capacitance, and conductance parameters, this paper introduces the distributed transmission line model of silicon-core coaxial through-silicon vias (CTSVs), in which the vertical interconnect is made of a Cu-coated silicon pole. The proposed model is validated against a commercial electromagnetic simulation tool, showing it is highly accurate up to 100 GHz. Using the proposed model, the impact of various material properties and physical parameters on the electrical performance of the silicon-core CTSVs is investigated. It is observed that the thickness of the plated Cu and isolation dielectric are two important parameters that determine the electrical performance of silicon-core CTSVs. Performance comparison shows that the proposed silicon-core CTSVs provide a comparable performance to standard Cu-based CTSVs and better performance to the conventional signal-ground TSV pairs. The results in this paper would provide some design guides for silicon-core CTSVs in 3-D integration.

Flexible Hybrid Electronics Technology Using Die-First FOWLP for High-Performance and Scalable Heterogeneous System Integration

Abstract: A technological platform is established for scalable flexible hybrid electronics based on a novel fan-out wafer-level packaging (FOWLP) methodology Small dielets are embedded in flexible substrates we call FlexTrate These dielets can be interconnected through high-density wirings formed in wafer-level processing We demonstrate homogeneous integration of 625 (25 by 25) 1-mm2 Si dielets and heterogeneous integration of GaAs and Si dielets with various thicknesses in a biocompatible polydimethylsiloxane (PDMS) In this paper, 8- $\mu \text{m}$ -pitch die-to-die interconnections are successfully implemented over a stress buffer layer formed on the PDMS In addition, coplanarity between the PDMS and embedded dielets, die shift concerned in typical die-first FOWLP, and the bendability of the resulting FlexTrate are characterized

High-Frequency Characterization and Modeling of Coaxial Connectors With Degraded Contact Surfaces

Abstract: Coaxial connectors provide a means to connect and disconnect transmission lines, components, and systems at high signal frequencies. Connector contact degradation has a significant effect on signal transmissions. This paper considers experimental measurements, simulations, and analyses of the high-frequency behaviors of degraded coaxial connector. An experimental investigation was first performed to evaluate how degraded contact surfaces affect the return loss and insertion loss of connectors. It was found that both the input return loss and the insertion loss are frequency-dependent. As the contact surface degrades, the return loss decreases and the insertion loss increases at lower frequencies, with the effect of the degradation becoming smaller with increasing frequency. A 3-D field simulation was developed to evaluate the high-frequency performance of various contact cases. Based on the simulation results, the electrical parameters of the dielectric film were extracted for connectors with different degradation levels. According to the transmission line theory and the contact physics, a high-frequency equivalent model of the degraded coaxial connector was developed and analyzed. This model is helpful in developing a better understanding of possible failure modes and in identifying failure features in fault diagnosis.

Direct-Acting Piezoelectric Jet Dispenser With Rhombic Mechanical Amplifier

Abstract: In order to tackle jet motion interference between a needle and guiding part, a new piezoelectric jet dispenser based on the rhombus magnifying principle is proposed. The new jet dispenser can jet 1.4-Pa · s adhesive without preheating, which can deliver 100 adhesive dots per second. The lifespan of the nozzle and needle exceeds 20 million cycles. It will provide a new device for adhesive distribution, and the amplifying method also fits other piezoelectric applications.

Design of Miniaturized Dual-Band Low-Pass–Bandpass and Bandpass Filters

Abstract: In this paper, a lumped-element structure with four potential transmission zeros (TZs), one zero-value transmission pole (TP), and three nonzero TPs is first proposed to design dual-band low-pass-bandpass filter (DB-LBF). Then, a pair of capacitors to block zero-value TP and an inductor to generate another nonzero TP are introduced in the DB-LBF structure to transform the low-pass passband into bandpass passband, so that a dual-band bandpass filter (DB-BPF) is constituted. Closed formulas and guidelines are given for two types of filter design. As examples, a 0.9/2.4-GHz DB-LBF with compact size of $0.05\lambda _{g\_{}{\mathrm{ lb}}}\times 0.079\lambda _{g\_{}{\mathrm{ lb}}}$ and a 0.395/1.575-GHz DB-BPF with compact size of $0.032\lambda _{g\_{}{\mathrm{ bb}}}\times 0.027\lambda _{g\_{}{\mathrm{ bb}}}$ are designed and fabricated. Both DB-LBF and DB-BPF have two independently controlled passband frequencies and also exhibit wide passband, low insertion loss, good return loss, and sharp passband selectivity. Moreover, they are also compatible with integrated circuit process.

Zero-Gap Waveguide: A Parallel Plate Waveguide With Flexible Mechanical Assembly for mm-Wave Antenna Applications

Abstract: A new gap waveguide concept is presented, where the air gap between the perfect electric conductor and artificial magnetic conductor (AMC) parallel plates of a conventional gap waveguide structure has been reduced to almost zero. When the air gap is reduced, the periodic metal pin layer (which emulates the AMC characteristics) may come in contact with the top metal layer. A statistical analysis of a random contact of the pin texture and the top metal plate in this new type of gap technology guiding structure, so-called zero-gap, is elaborated in this paper. The periodic pin texture creates a stopband for parallel plate modes, and it is also used as a mechanical support while assembling the waveguide structure. This presents a significant manufacturing advantage, especially for corporate feed-network of array antennas at millimeter-wave frequencies. A $V$ -band $8\times 8$ slot array fed with this new waveguide is also designed and manufactured to show the potential of this newly proposed zero-gap waveguide structure. The measured results show 20% of relative impedance bandwidth ( $|S_{11}| dB) and an overall antenna efficiency larger than 60% over the 56.5–69-GHz frequency band.

Aerosol-Printed Highly Conductive Ag Transmission Lines for Flexible Electronic Devices

Abstract: We studied aerosol jet printing on flexible substrates for wearable and flexible electronic devices First, we investigated the electrical conductivity of aerosol jet printed silver layers at different temperatures An electrical conductivity up to 60% of bulk Ag was measured after sintering at 140 °C on a hot plate Higher conductivities became possible with higher sinter temperatures The printed ink showed a surprisingly high flexibility Transmission lines were printed on flexible substrates [Kapton and Rogers liquid crystal polymer (LCP) foils], and the performance was measured up to 110 GHz The coplanar waveguide transmission lines demonstrated insertion losses of 0366 dB/mm for LCP and 0546 dB/mm for Kapton foils at 110 GHz

Theory of Thermal Time Constants in GaN High-Electron-Mobility Transistors

Abstract: Due to the high dissipated power densities present in GaN high-electron-mobility transistors (HEMTs) in high-power radio frequency applications, thermal analysis and thermal management of these devices are important in achieving their full potential. In this paper, we present a fundamental study of the transient thermal behavior of GaN HEMTs to aid in understanding the complex contributions of multidimensional thermal spreading, multiple epitaxial layers, multiple gate fingers, and thermal boundary resistance to the temperature rise. This complex behavior cannot be accurately described by one or two thermal time constants. Rather, a broad spectrum of time constants from ~1 ns up to several milliseconds are present in the device due to aggressive multidimensional thermal spreading from the narrow region of power dissipation next to each HEMT gate through the substrate, die attach, and package. In order to accurately model the temperature response, at least one time constant per decade over the timescale of interest is required. These findings are crucial in developing an intuitive understanding of the transient thermal behavior of GaN HEMTs and properly accounting for transient temperature rise in electrothermal modeling of high-power GaN-based amplifiers.

Stencil Printing Process Optimization to Control Solder Paste Volume Transfer Efficiency

Abstract: This research aims to optimize the stencil printing parameters to control the solder paste volume TE and increase the first-pass-yields of printed circuit boards (PCBs). Stencil printing process (SPP) factors considered in this research are related to solder paste composition, product configuration, printer setup, and stencil design. Support vector regression (SVR) with different kernels and regression tree (RT) are used to estimate the solder paste volume transfer efficiency (TE) and capture the nonlinear relationships between the SPP factors and volume TE. A novel mixed-integer nonlinear programming (MINLP) model is proposed to optimize the printing parameters for different PCB configurations of pads. The $\epsilon$ -constraint approach is used to solve the proposed MINLP model using metaheuristics, such as simulated annealing (SA) and evolutionary strategies (ES). The experimental results indicate relatively high ${R}^{2}$ values of 81% and 72% for average and standard deviation volume TE models that use SVR and RT, respectively. Then, the optimal printing parameters for certain pads’ configuration are retrieved for different volume TE spec limits. The results show that SA and ES can find optimal solutions for the spec limits of 50%–150%, 70%–130%, and 80%–120%.

A Study on the Optimization of Anisotropic Conductive Films for Sn-3Ag-0.5Cu-Based Flex-on-Board Application at a 250 °C Bonding Temperature

Abstract: Although cationic epoxy was optimized for low-melting SnBi58 solder ACF joints with the lowest coefficient of thermal expansion (CTE) in terms of reliability, cationic epoxy also showed a faster curing property than any other types of adhesives. In fact, solder joint shapes at 250 °C bonding are very different from those shapes at 200 °C bonding. In this paper, four adhesive film types were investigated in terms of Sn-3Ag-0.5Cu solder ACF joint shapes on the electrical performances and reliability in a pressure cooker test (PCT). Thermal stability of adhesive films was tested to be first. Resin curing speeds were measured in a 250 °C isothermal mode differential scanning calorimetry, resin viscosities were checked by a parallel-plate rheometer, and adhesive thermomechanical properties, such as modulus and CTE, were characterized. Then, four different types of ACF resins containing the same weight percentages of Sn-3Ag-0.5Cu solders were assembled by the same thermocompression bonding parameter (250 °C 10s 2MPa on bump) on a 500- $\mu \text{m}$ -pitch flex-on-board (FOB) application, and different solder joint morphologies were verified. Various bonded solder ACFs joints were compared in terms of solder wetting areas, electrical performances by a four-point-probe method, and the reliability of PCT (121 °C 100% humidity 2atm) for 120 h. This paper aims at optimizing the best adhesive film candidate for SAC305 solder ACF joints of FOB application.