Showing papers in "IEEE Transactions on Components, Packaging and Manufacturing Technology in 2015"

3-D Printed Metal-Pipe Rectangular Waveguides

Abstract: This paper first reviews manufacturing technologies for realizing air-filled metal-pipe rectangular waveguides (MPRWGs) and 3-D printing for microwave and millimeter-wave applications. Then, 3-D printed MPRWGs are investigated in detail. Two very different 3-D printing technologies have been considered: low-cost lower-resolution fused deposition modeling for microwave applications and higher-cost high-resolution stereolithography for millimeter-wave applications. Measurements against traceable standards in MPRWGs were performed by the U.K.’s National Physical Laboratory. It was found that the performance of the 3-D printed MPRWGs were comparable with those of standard waveguides. For example, across X-band (8–12 GHz), the dissipative attenuation ranges between 0.2 and 0.6 dB/m, with a worst case return loss of 32 dB; at W-band (75–110 GHz), the dissipative attenuation was 11 dB/m at the band edges, with a worst case return loss of 19 dB. Finally, a high-performance W-band sixth-order inductive iris bandpass filter, having a center frequency of 107.2 GHz and a 6.8-GHz bandwidth, was demonstrated. The measured insertion loss of the complete structure (filter, feed sections, and flanges) was only 0.95 dB at center frequency, giving an unloaded quality factor of 152—clearly demonstrating the potential of this low-cost manufacturing technology, offering the advantages of lightweight rapid prototyping/manufacturing and relatively very low cost when compared with traditional (micro)machining.

Fundamental Cooling Limits for High Power Density Gallium Nitride Electronics

Abstract: The peak power density of GaN high-electron-mobility transistor technology is limited by a hierarchy of thermal resistances from the junction to the ambient Here, we explore the ultimate or fundamental cooling limits for junction-to fluid cooling, which are enabled by advanced thermal management technologies, including GaN–diamond composites and nanoengineered heat sinks Through continued attention to near-junction resistances and extreme flux convection heat sinks, heat fluxes beyond 300 kW/cm $^{2}$ from individual 2- $\mu \text{m}$ gates and 10 kW/cm $^{2}$ from the transistor footprint will be feasible The cooling technologies under discussion here are also applicable to thermal management of 25-D and 3-D logic circuits at lower heat fluxes

Screen Printing of Multilayered Hybrid Printed Circuit Boards on Different Substrates

Abstract: This paper reports on the successful fabrication of a multilayered hybrid printed circuit board (PCB) for applications in the consumer electronics products, medical technologies, and military equipment. The PCB was fabricated by screen-printing silver (Ag) flake ink, as metallization layer, and UV acrylic-based ink, as dielectric layer, on different substrates such as paper, polyethylene terephthalate, and glass. Traditional electronic components were attached onto the printed pads to create the multilayered hybrid PCB. The feasibility of the hybrid PCB was demonstrated by integrating an embedded microcontroller to drive an liquid-crystal display ( $160\times 100$ pixels). In addition, the amount of the ink spreading after printing, the effect of bending on the printed lines, and the effect of the roughness of the substrates on the resistance of the printed lines was investigated. It was observed that the resistance of the lines increased by $\approx 1.8$ %, after 10 000 cycles of bending, and the lowest resistance of 1.06 $\Omega $ was measured for the 600 $\mu $ m printed lines on paper, which had a roughness of 0.175 $\mu $ m. The advantage of fabricating PCBs on flexible substrates is the ability to fold and place the boards on nearly any platform or to conform to any irregular surface, whereas the additive properties of printing processes allow for a faster fabrication process, while simultaneously producing less material waste in comparison with the traditional subtractive processes. The results obtained show the promising potential of employing screen printing process for the fabrication of flexible and light-weight hybrid PCBs.

Survey of High-Temperature Polymeric Encapsulants for Power Electronics Packaging

Abstract: Semiconductor encapsulation is crucial to electronic packaging because it provides protection against mechanical stress, electrical breakdown, chemical erosions, α radiations, and so on. Conventional encapsulants are only applicable below 150 °C. However, with increasing demand for high-density and high-temperature packaging, encapsulants that are functional at or above 250 °C are required. In this paper, five types of encapsulants, including conformal coatings, underfills, molding compounds, potting compounds, and glob tops, are surveyed. First, recommended properties and selection criteria of each type of encapsulant are listed. Second, standard test methods for several crucial properties, including glass-transition temperature (T g ), coefficient of thermal expansion (CTE), dielectric strength, and so on are reviewed. Afterward, commercial products with high-operation temperature are surveyed. However, the results of the survey reveal a lack of high-temperature encapsulants. Therefore, this paper reviews recent progress in achieving encapsulants with both high-temperature capability and satisfactory properties. Material compositions other than epoxy, such as polyimide (PI), bismaleimide (BMI), and cyanate ester (CE), are potential encapsulants for high-temperature (250 °C) operation, although their CTE needs to be tailored to limit internal stress. Fillers are reported to be efficient in reducing the CTE. In addition, fillers may also have a beneficial impact on the thermal stability of silicone-based encapsulants, whose high-temperature capability is limited by their thermal instability.

An ME-PC Enhanced HDMR Method for Efficient Statistical Analysis of Multiconductor Transmission Line Networks

Abstract: An efficient method for statistically characterizing multiconductor transmission line (MTL) networks subject to a large number of manufacturing uncertainties is presented. The proposed method achieves its efficiency by leveraging a high-dimensional model representation (HDMR) technique that approximates observables (quantities of interest in MTL networks, such as voltages/currents on mission-critical circuits) in terms of iteratively constructed component functions of only the most significant random variables (parameters that characterize the uncertainties in MTL networks, such as conductor locations and widths, and lumped element values). The efficiency of the proposed scheme is further increased using a multielement probabilistic collocation (ME-PC) method to compute the component functions of the HDMR. The ME-PC method makes use of generalized polynomial chaos (gPC) expansions to approximate the component functions, where the expansion coefficients are expressed in terms of integrals of the observable over the random domain. These integrals are numerically evaluated and the observable values at the quadrature/collocation points are computed using a fast deterministic simulator. The proposed method is capable of producing accurate statistical information pertinent to an observable that is rapidly varying across a high-dimensional random domain at a computational cost that is significantly lower than that of gPC or Monte Carlo methods. The applicability, efficiency, and accuracy of the method are demonstrated via statistical characterization of frequency-domain voltages in parallel wire, interconnect, and antenna corporate feed networks.

Mechanical Designs for Inorganic Stretchable Circuits in Soft Electronics

Abstract: Mechanical concepts and designs in inorganic circuits for different levels of stretchability are reviewed in this paper, through discussions of the underlying mechanics and material theories, fabrication procedures for the constituent microscale/nanoscale devices, and experimental characterization. All of the designs reported here adopt heterogeneous structures of rigid and brittle inorganic materials on soft and elastic elastomeric substrates, with mechanical design layouts that isolate large deformations to the elastomer, thereby avoiding potentially destructive plastic strains in the brittle materials. The overall stiffnesses of the electronics, their stretchability, and curvilinear shapes can be designed to match the mechanical properties of biological tissues. The result is a class of soft stretchable electronic systems that are compatible with traditional high-performance inorganic semiconductor technologies. These systems afford promising options for applications in portable biomedical and health-monitoring devices. Mechanics theories and modeling play a key role in understanding the underlining physics and optimization of these systems.

Assembly and Packaging Technologies for High-Temperature and High-Power GaN Devices

Abstract: This paper gives a detailed analysis on the assembly and packaging technologies for the state-of-the-art GaN-based high-electron-mobility transistors, which are suitable for high-temperature and high-power applications. Silver sintering and transient liquid phase bonding were selected as die-attachment techniques, and gold and palladium were investigated for electrical interconnection materials. Both the die-attachments were characterized for their high-temperature stability up to 450 °C. Systematic electrical characterizations were performed from on-wafer measurements to the final assembly. The thermal and thermomechanical influences of the assembly were assessed. For die-attachments and interconnections, passive temperature shock cycling and active power cycling were performed as an initial attempt to characterize the assembly reliability. Finally, a complete package along with the base plate was proposed, which can survive high temperatures up to 480 °C.

Pressureless Sintering of Microscale Silver Paste for 300 °C Applications

Abstract: High-temperature die attach is necessary to fabricate digital and analog thick film modules for 300 °C applications Sintered Ag is a promising die attach material, but typically requires pressure during sintering for larger die Pressureless sintering of a microscale Ag paste has been evaluated with Au and Ag die metallization on Au, Ag, and PdAg thick film metalized substrates With Au metallization on either the die or the substrate, degradation of shear strength rapidly occurred with aging at 300 °C Formation of a dense Ag layer and a depletion region near the Au surface was observed with 300 °C aging This was attributed to the rapid surface diffusion of Ag on Au surfaces at 300 °C This did not occur with Ag thin film die metallization and Ag and PdAg thick film metallization After 8000 h at 300 °C, $8 {\rm mm} \times 8$ mm Ag metalized die on Ag thick film substrates could not be sheared at 100 kg of applied force The same was true for $8 {\rm mm}\times 8$ mm Ag metalized die on PdAg thick film substrates after 2000 h at 300 °C

Integration of a 140 GHz Packaged LTCC Grid Array Antenna With an InP Detector

Abstract: Integration of a 140-GHz packaged low-temperature cofired ceramic (LTCC) antenna with a power detector is demonstrated under the concept of antenna-in-package. The detector is designed on an indium phosphide (InP) process. A grid array antenna in LTCC is designed to provide package for the detector. Coplanar ground–signal–ground (GSG) bond wires are used to connect the detector and the antenna. Parallel plate mode is observed in the InP substrate and absorbed by the LTCC substrate. The comparison between the measured responsivity of the power detector with and without the antenna indicates the acceptable insertion loss of the coplanar GSG bond wires transition. It shows a feasible solution for the D-band front-end integration and packaging.

Lumped Dynamic Electrothermal Model of IGBT Module of Inverters

Abstract: This paper presents a lumped dynamic electrothermal model of an insulated gate bipolar transistor module of inverters. The thermal model consists of a 3-D network of $RC$ cells constructed for time-dependent operation. The network was found to be precise for determining the temperature excursion of diodes and transistors subsequent to time-dependent power losses. Thermal resistances and capacitances accounting for heat spreading and thermal penetration depth effects were introduced. Electrothermal simulations carried out on a 1200 V–300 A module with a time-dependent average power loss were found to be in good agreement with experiments using infrared thermal imaging. This paper focuses on very-low-frequency behavior (less than 1 Hz) at a switching frequency of 10 kHz.

Reliability Comparison of Aged SAC Fine-Pitch Ball Grid Array Packages Versus Surface Finishes

Abstract: Pb-free solder joints exposed to elevated isothermal temperatures for prolonged periods of time undergo microstructural and mechanical evolution, which degrades the joint electrical performance. We report the effect of isothermal aging on the reliability of Sn–Ag–Cu (SAC) assemblies on three different surface finishes [immersion Ag (ImAg), electroless Ni/immersion Au (ENIG), and electroless Ni/electroless Pd/immersion Au (ENEPIG)]. The characteristic life for SAC alloys in 10- and 15-mm ball grid array packages on ImAg degraded over 40% after an 85 °C/12 months aging and over 50% during a 125 °C/12 months aging. ENIG and ENEPIG outperformed ImAg for all aging treatments. For passive components (2512 resistors) on ImAg, the reliability performance degraded 16.7%/28.1% after a 1-year aging at 85 °C/125 °C. Failure analysis showed dramatic intermetallic binary Cu–Sn and ternary Ni–Cu–Sn film growth at the bottom of the solder joint interfaces for ImAg and ENIG/ENEPIG. For 125 °C-aged samples, the cracks appeared at the corners of both package and board sides of the solder ball and propagated along (near) the intermetallic compound location. For the case of aged fine-pitch packages, the failures tended to start at the component side solder ball corner and then propagate along an angled path downward into the bulk solder.

A Fully Adaptive Scheme for Model Order Reduction Based on Moment Matching

Abstract: A fully adaptive model order reduction scheme based on moment matching is proposed to derive the reduced-order models of linear time-invariant (LTI) systems. According to the given error tolerance, the order of the reduced-order model as well as the expansion points for the transfer function is automatically determined on the fly during the process of model reduction. In this sense, the reduced-order model is automatically obtained without assigning the number of moments and expansion points in a priori , which is a prerequisite for the standard implementation of model reduction based on moment matching. The proposed adaptive scheme is found to be efficient when it is tested on various LTI systems.

High-Selectivity Low-Pass Filters With Ultrawide Stopband Based on Defected Ground Structures

Abstract: Compact microstrip low-pass filters (LPFs) with ultrawide stopband based on a defected ground structure (DGS) and their design procedures are presented in this paper. A key merit of the filter configuration is that the selectivity of the LPFs can be conveniently controlled, whereas the bandwidth is fixed. The LPFs are realized using open-circuited uniform impedance stubs and stepped-impedance stubs (SISs). The position of the transmission zeros can be freely controlled by tuning the impedance ratio of the SISs. To expand the stopband, the dumbbell DGS is used to suppress the spurious passbands of the LPFs. Two demonstration filters with a cutoff frequency at 1 GHz have been designed, fabricated, and measured. The measured results indicate good performance: broad stopband ( $>15 f_{c}$ or $20~f_{c}$ ), low passband insertion loss (<0.3 dB), compact size, and sharp skirt characteristic.

Remaining-Life Prediction of Solder Joints Using RF Impedance Analysis and Gaussian Process Regression

Abstract: Solder joints are among the most common failure sites in electronic assemblies. This paper presents a prognostic approach that allows for the remaining useful life prediction of solder joints using an RF impedance analysis and the Gaussian process (GP) regression. While the solder joints were exposed to a mechanical stress condition to generate fatigue failures, the RF impedance of the solder joint was continuously monitored. The RF impedance provided an early indication of the impending solder-joint failure in the form of a gradual increase prior to the end of life. A GP model was applied to the RF impedance obtained from the fatigue tests in order to estimate the remaining life of the solder joint in real time. It was demonstrated that the GP model successfully predicted the time to failure of the solder joint with high accuracy prior to failure. The prediction performance was also evaluated using prognostic metrics.

Metal Proportion Optimization of Annular Through-Silicon via Considering Temperature and Keep-Out Zone

Abstract: For annular through-silicon via (TSV)-based 3-D integrated circuits (3-D ICs), a greater TSV metal proportion of annular TSV leads to lower temperature but induces larger keep-out zone (KOZ). In this paper, the figure of merit (FOM) tradeoff model between temperature and KOZ is proposed to obtain the optimal metal proportion of annular TSV. First, the analytical models of the temperature of annular TSV-based 3-D IC and the KOZ induced by annular TSV are given, respectively, and both of them are verified by ANSYS software. Second, based on the analytical models, the FOM model is proposed. Then, the effects of total radius, material, and insertion density of annular TSV on FOM and optimal metal proportion are analyzed in detail. It is concluded that, the optimal metal proportion of annular TSV is approximately 0.3 with large ranges of the total radius and density of annular TSV, and various materials filled in annular TSV.

High-Aspect-Ratio Through Silicon Vias for High-Frequency Application Fabricated by Magnetic Assembly of Gold-Coated Nickel Wires

Abstract: In this paper, we demonstrate a novel manufacturing technology for high-aspect-ratio vertical interconnects for high-frequency applications This novel approach is based on magnetic self-assembly of prefabricated nickel wires that are subsequently insulated with a thermosetting polymer The high-frequency performance of the through silicon vias (TSVs) is enhanced by depositing a gold layer on the outer surface of the nickel wires and by reducing capacitive parasitics through a low- $k$ polymer liner As compared with conventional TSV designs, this novel concept offers a more compact design and a simpler, potentially more cost-effective manufacturing process Moreover, this fabrication concept is very versatile and adaptable to many different applications, such as interposer, micro electromechanical systems, or millimeter wave applications For evaluation purposes, coplanar waveguides with incorporated TSV interconnections were fabricated and characterized The experimental results reveal a high bandwidth from dc to 86 GHz and an insertion loss of $ dB per single TSV interconnection for frequencies up to 75 GHz

Design of Anisotropic Thermal Conductivity in Multilayer Printed Circuit Boards

Abstract: The design of anisotropic thermal conductivity in multilayer printed circuit boards (PCB) is studied, where the flow of heat is manipulated through the informed layout of circuit board electrothermal traces. Three representative circuit board configurations are considered to illustrate the basic method. A baseline circuit board (Configuration 1) comprising a heat-generating device in thermal communication with a heat sensitive device by the way of a standard electrical trace connection is studied first to characterize heat flow due to conduction and convection. Building off of this baseline structure, the thermal management advantages and disadvantages of a closed heat shield for anisotropic PCB thermal conductivity are explored using the second circuit board (Configuration 2). The design of the third multilayer circuit board (Configuration 3) with optimized anisotropic PCB thermal conductivity for enhanced heat flow control is simultaneously explored. It is experimentally shown that, for PCBs subject to free convection and power densities on the order of 1–10 W/cm2, the design technique allows for noticeable (−10 °C) reduction in the temperature of the heat sensitive device without a significant (<3 °C) increase in the heat-generating device temperature. The experimental heat transfer results are verified through simulations that further confirm and explain the functionality and limitations of the heat flow control concept. The effect of Joule heating is also investigated numerically. A conceptual framework for electrothermal codesign of multilayer PCBs with integrated heat flow control and more device-dense packaging is proposed.

An Unconditionally Stable FDTD Model for Crosstalk Analysis of VLSI Interconnects

Abstract: In this paper, an unconditionally stable finite-difference time-domain (US-FDTD) model is proposed for the crosstalk noise analysis of coupled very large scale integration interconnects. The accuracy of the proposed model is validated against the conventional FDTD model and HSPICE. It is observed that the proposed model is as accurate as the conventional FDTD and HSPICE. It is also observed that the stability of the proposed model is not constrained by the Courant–Friedrichs–Lewy stability condition. Depending on the time-step size, the proposed model can be up to $100\times $ faster than the conventional FDTD.

Miniaturized Dual-Band Wilkinson Power Divider With Self-Compensation Structure

Abstract: A miniaturized dual-band Wilkinson power divider with a parallel $LC$ circuit at the midpoints of two coupled-line sections is proposed in this paper. General design equations for parallel inductor $L$ and capacitor $C$ are derived from even- and odd-mode analysis. Generally speaking, characteristic impedances between even and odd modes are different in two coupled-line sections, and their electrical lengths are also different in inhomogeneous medium. This paper proved that a parallel $LC$ circuit compensates for the characteristic impedance differences and the electrical length differences for dual-band operation. In other words, the proposed model provides self-compensation structure, and no extra compensation circuits are needed. Moreover, the upper limit of the frequency ratio range can be adjusted by two coupling strengths, where loose coupling for the first coupled-line section and tight coupling for the second coupled-line section are preferred for a wider frequency ratio range. Finally, an experimental circuit shows good agreement with the theoretical simulation.

U-Shape Slots Structure on Substrate Integrated Waveguide for 40-GHz Bandpass Filter Using LTCC Technology

Abstract: Millimeter-wave (mmW) bandpass filter using substrate integrated waveguide (SIW) is proposed in this paper The propagation constants of three different types of electromagnetic bandgap (EBG) units are discussed and compared with their passbands and stopbands performance The slotted-SIW unit shows a very good lower stopband and upper stopband performance The mmW bandpass filter with three cascaded uniform slotted-SIW-based EBG units is constructed and designed at 40 GHz The extracted coupling coefficient ( ${K}$ ) and quality factor ( ${Q}$ ) are used to determine the filter circuit dimensions To prove the validity, the previous proposed structure is fabricated in a single circuit layer using low-temperature co-fired ceramic technology and measured at 40 GHz, respectively The measured results are in good agreement with simulated results in such frequency and the measured insertion losses at 40 GHz is 142 dB, respectively

Correlation Between Solder Joint Fatigue Life and Accumulated Work in Isothermal Cycling

Abstract: The fatigue behavior of solder joints in realistic service applications is still not well understood. Service life prediction based on conducting accelerated tests and extrapolating test results therefore involves a high potential for error. Understanding both the evolution of solder joint properties and the damage accumulation has proved to be critical to reliability modeling. Damage accumulation in isothermal cycling is shown to scale with the accumulated inelastic work even in complex cycling scenarios, so that the life of a solder joint ends upon accumulation of a given amount of work. Individual ball grid array solder joints were cycled in shear fatigue experiments with different load amplitudes and strain rates. The effects of load amplitudes and strain rates on the work accumulation and fatigue life were systematically addressed. The correlation between different loading scenarios and the accumulated work to failure was also discussed. The results showed that the accumulated work until the development of a major crack is constant regardless of the load amplitude. After that the accumulated work to failure is lower for larger load amplitudes. For some reason, a larger fraction of the work appears to be dissipating as heat at lower load amplitude, but only during crack growth. On the other hand, the strain rate affects the fraction of the work going to heat even before the development of a major crack.

Impact of Copper Through-Package Vias on Thermal Performance of Glass Interposers

Abstract: In this paper, the thermal performance of glass interposer substrate with copper through-package vias (TPVs) is investigated both experimentally and numerically. Copper via arrays with different via pitches and diameters were fabricated in 114.3 mm $\times \,\, 114.3$ mm $\times \,\, 100\mu \text{m}$ glass panels using low-cost laser drilling, electroless plating, and electroplating for copper deposition. The thermal performance of such a structure was quantified by measuring an effective thermal conductivity which combines the effect of copper and glass. The effective thermal conductivity of fabricated samples was determined with infrared microscopy and compared with finite-element analysis on unit TPV cell. Using the effective thermal conductivity, further numerical analyses were performed on a 2.5-D interposer, which has two chips mounted side by side with a total heat generation of 3 W. Interconnects and TPV layers in the interposer were modeled as homogeneous layers with an effective thermal conductivity. Using the developed model, the effect of copper TPVs on the thermal performance of silicon and glass interposers was compared. To further characterize the thermal performance of the 2.5-D glass interposer structure, the effects of pitch of interconnects and TPVs and the TPV diameter are presented.

Substrate Integrated Meandering Probe-Fed Patch Antennas for Wideband Wireless Devices

Abstract: This paper presents novel linearly polarized (LP) and circularly polarized (CP) patch antennas for wideband wireless devices. Advanced electrical characteristics of the antennas including wide bandwidth, low cross polarization, low back radiation, and polarization insensitivity contribute to improve the signal quality of wireless connectivity. It is a realization of antenna foundation by employing multilayer microwave laminates to form a substrate integrated meandering probe-fed patch antenna. First, a design and analysis of the proposed patch antenna for LP operation is carried out. Based on the obtained results of this LP element, a substrate integrated meandering probe fed CP patch antenna is exhibited afterward. This paper is considered as a part of RF modules that could be integrated with other components like sensors, Microcontroller units, and electronic parts to form a wireless product by means of conventional packaging process.

Thermal Management of Hotspots Using Diamond Heat Spreader on Si Microcooler for GaN Devices

Abstract: A diamond heat spreader has been applied on the hybrid Si microcooler for the improvement of the hotspots cooling capability for GaN devices. The microwave chemical vapor deposition diamond heat spreader under tests is of thickness 400 $\mu \text{m}$ and thermal conductivity as high as $1500\sim 2000$ W/mK, and is bonded through the thermal compression bonding process at chip level. Eight hotspots, each of size $450\times 300~\mu \text{m}^{2}$ , were fabricated on a Si thermal test chip to mimic the heating areas of eight GaN units. Heat dissipation capabilities were studied and compared through experimental tests and thermal/fluid simulations, and consistent results have been obtained. Using the diamond heat spreader, to dissipate 70-W heating power, the maximum chip temperature can be reduced by 40.4% and 27.3%, compared with the structure without a heat spreader and the one with a copper heat spreader, respectively. While maintaining the maximum hotspot temperature under 160 °C, 10-kW/cm $^{\mathrm {{2}}}$ hotspot heat flux can be dissipated. The thermal effects of the heat spreader thickness, the diamond thermal conductivity, and the bonding layer are investigated. Based on the simulation results, the higher power density of the GaN device can be dissipated, while maintaining the peak gate temperature under 200 °C. The concentrated heat flux has been effectively reduced using a diamond heat spreader, and much better cooling capability of the Si microcooler has been achieved for high-power GaN devices.

A Novel Model of Reliability Assessment for Circular Electrical Connectors

Abstract: The reliability of circular electrical connectors was usually assessed according to standards like MIL-HDBK-217 (Reliability Prediction of Electronic Equipment). Given to their limitations and mislead results, a new assessment method needs to be presented. Some concerns on the physics of failure (PoF) modeling and reliability assessment of circular electrical connectors are addressed in this paper to overcome this defect. An original approach combining laboratory accelerated degradation testing (ADT) and PoF modeling is proposed for effectively assessing connector reliability. Random vibration and current stress are selected as acceleration factors that affect the contact life of electrical connectors. Then, an appropriate multiple-stresses ADT scheme is derived. The PoF model for electrical connectors under multiple stresses yielded the generalized Eyring relationship. According to the system reliability model for multiposition connectors, connectors’ life follows Weibull distribution, which is derived from extreme-value distribution theory. Through ADT and data gained from tests, statistical analysis result yielded the estimated value of reliability character of MIL-C-38999 I series electrical connectors under the action of vibration and current stresses.

Novel LTCC Distributed-Element Wideband Bandpass Filter Based on the Dual-Mode Stepped-Impedance Resonator

Abstract: In this paper, a novel compact 3-D dual-mode stepped-impedance resonator (SIR) with centrally loaded stub is constructed for designing a wideband low-temperature cofired ceramic (LTCC) bandpass filter (BPF). By fully taking advantage of the LTCC technology, the dual-mode SIR, as a cell unit of the proposed filter, is reasonably folded in 3-D environment, and its properties are investigated using the transmission line theory. Accordingly, benefiting from the 3-D circuit layout, the proposed BPF designed by combining the SIR and dual-mode techniques can effectively overcome a vital and common drawback of large circuit size of the LTCC distributed-element filters. For demonstration, a fourth-order wideband BPF centered at 5 GHz is designed, fabricated, and measured. The circuit size of the designed BPF has a compact size of $3.875\times 4.8\times 1.4$ mm $^{3}$ . The impact of the package on the coupling and routing scheme and frequency response/transmission zero has been analyzed and demonstrated. The simulated and measured results are presented and compared, showing a good agreement.

Thermal Remote Phosphor Coating for Phosphor-Converted White-Light-Emitting Diodes

Abstract: We demonstrated a thermal remote phosphor coating method for realizing high angular color uniformity (ACU) and high efficiency of phosphor-converted white-light-emitting diodes based on thermal control. The proposed phosphor-coating method can fabricate remote phosphor layer geometries through a simple package process. Experimental results show that compared with those samples packaged by conventional dispensing coating, this method can efficiently improve the ACU. Angular color-correlated temperature (CCT) deviation of the test samples by the present method can reduce from 1100 to 90 K for an average CCT of 4300 K from −90° to +90° view angles, and the CCT distributions are 150 and 250 K for average CCTs of 5300 and 6300 K, respectively. In addition, this method can improve the lumen efficiency by 4.45% for an average CCT of about 4300 K, and increased by 4.96% and 5.45% for average CCTs of 5300 and 6300 K, respectively.

An Investigation of the Ink-Transfer Mechanism During the Printing Phase of High-Resolution Roll-to-Roll Gravure Printing

Abstract: Reducing the linewidth of electrodes is of high importance for increasing not only the efficiency of photovoltaic devices but also the performance of organic thin-film transistors In particular, controlling the line pattern in printing processes has been difficult In this paper, we report an analytical approach for obtaining high-resolution control over the ink-transfer mechanism in roll-to-roll (R2R) gravure printing A dimensionless adhesion-force difference was defined for a simple ink-transfer model, and it was used to predict and evaluate the ink-transfer mechanism with respect to several parameters, such as the surface tension of the ink, surface energy of the substrate, and surface energy and aspect ratio (AR) of the cell It was found that the low-surface-tension inks, high-surface-energy substrates, and low-surface-energy and high-AR cells are preferable to increasing the ink-transfer ratio during the printing phase Finally, a matching-logic flowchart was developed for controlling the ink-transfer mechanism and fidelity of R2R gravure printing The printed patterns obtained had an average width as small as 153 $\mu \text{m}$ (standard deviation $= \,\, 09~\mu \text{m}$ )

Performance-Governing Transport Mechanisms for Heat Pipes at Ultrathin Form Factors

Abstract: Heat pipes and vapor chamber heat spreaders offer a potential solution to the increasing thermal management challenges in thin-form-factor mobile computing platforms, where efficient spreading is required to simultaneously prevent overheating of internal components and formation of hot regions on the device exterior surfaces. Heat pipe performance limitations unique to such ultrathin form factors and the key heat transfer mechanisms governing the performance must be characterized. A thermal resistance network model and a detailed 2-D numerical model are used to analyze the performance of heat pipes under these conditions. A broad parametric study of geometries and heat inputs using the reduced-order model helps delineate the performance thresholds within which the effectiveness of a heat pipe is greater than a comparable solid heat spreader. A vapor-phase threshold unique to ultrathin heat pipes operating at low-power inputs is observed. At this threshold, the vapor-phase thermal resistance imposed by the saturation pressure/temperature gradient in the heat pipe causes a crossover in the thermal resistance relative to a solid heat spreader. The higher fidelity numerical model is used to assess the accuracy of the resistance network model and to verify the validity and applicability of each assumption made regarding the transport mechanisms. Key heat transfer mechanisms not captured by the reduced-order thermal network models are identified. These include the effects of boundary conditions on the interface mass flux profile, convective effects on the vapor core temperature drop, and 2-D conduction on smearing of evaporation/condensation mass flux into the adiabatic section.

Design of Sext-Band Bandpass Filter and Sextaplexer Using Semilumped Resonators for System in a Package

Abstract: In this paper, using semilumped resonators, one sext-band bandpass filter and one sextaplexer are proposed. The two circuits are fabricated using microstrip technology, and the semilumped resonator consists of two identical microstrip lines and a chip inductor at the center. In comparison with conventional half-wavelength uniform resonator, the semilumped resonator is compact and has better control over harmonic frequencies. In addition, the two circuits utilize a distributed coupling technique to integrate bandpass channel filters. This technique has a low loading effect resulting in a high design freedom that is essential for multiband circuits.