Blind Vias Research Articles

Evaluating copper plating process for filling micro vias with thin surface Cu by the 1-(4-carboxyphenyl)-5-mercapto-1H-tetrazole additive

The 1-(4-carboxyphenyl)-5-mercapto-1 h-tetrazole (CMHT) as a novel leveler for the overfilling of micro-blind vias was investigated in acidic copper electroplating. The synergistic effect between CMHT and other additives were confirmed through chronoamperometry, cyclic voltammetry and electrochemical impedance spectroscopy. The results showed a convection-dependent interaction between the CMHT and suppressor (propyleneoxide (PO)-ethylene oxide (EO)-propylene oxide (PO), named PEP). Metallographic section testing demonstrated that the CMHT not only have excellent microvia filling performances, but also only have 19.1 μm thin surface Cu for micro blind vias with a diameter of 150 µm and a depth of 80 µm by the electrodepositing 60 min of 2 A/dm2. The quantum chemical calculations experiments revealed also that the CMHT parallel orientation of the benzene ring and tetrazole heterocycle can enhance the effective adsorption area. The obtained results from electrochemical test and quantum chemical calculations were in reasonably good agreement.

Scalable Fabrication of Large-Scale, 3D, and Stretchable Circuits.

Stretchable electronics have demonstrated excellent potential in wearable healthcare and conformal integration. Achieving the scalable fabrication of stretchable devices with high functional density is the cornerstone to enable the practical applications of stretchable electronics. Here, a comprehensive methodology for realizing large-scale, 3D, and stretchable circuits (3D-LSC) is reported. The soft copper-clad laminate (S-CCL) based on the "cast and cure" process facilitates patterning the planar interconnects with the scale beyond 1 m. With the ability to form through, buried and blind VIAs in the multilayer stack of S-CCLs, high functional density can be achieved by further creating vertical interconnects in stacked S-CCLs. The application of temporary bonding substrate effectively minimizes the misalignments caused by residual strain and thermal strain. 3D-LSC enables the batch production of stretchable skin patches based on five-layer stretchablecircuits, which can serve as a miniaturized system for physiological signals monitoring with wireless power delivery. The fabrications of conformal antenna and stretchable light-emitting diode display further illustrate the potential of 3D-LSC in realizing large-scale stretchable devices.

Voiding in Parylene-C Encapsulation of Surface Mount LEDs for an Optogenetic Epilepsy Neuroprosthesis

It is often assumed that Parylene-C encapsulation films are void-free & conformal by nature of their vapour deposition. We present a case study in an optrode device where voiding occurs; we argue the voids originate from the geometry of the substrate and from the use of surface mount components. The segment under study consists of a commercial LED bonded with Au/Au thermosonic bonding onto a custom silicon substrate. We demonstrate via micro-sectioning that there is polymer voiding behaviour (1) in sub-LED surfaces; and (2) within through-hole vias in the silicon substrate (channels designed to allow polymer vapour ingress during deposition). By making a comparison to the solutions found in the IC industry around tungsten vapour filling of blind vias, we present geometric solutions for failure mitigation.

Investigation on tuning capabilities of self-diplexing antenna using different liquid dielectrics

This article investigates the possibilities of frequency tuning of a Self-diplexing antenna (SDA) using different liquid dielectrics. Tuning analysis is carried out using the fluidic pockets introduced into the substrate by drilling blind vias starting at the bottom layer. To examine the frequency tuning, the pockets can be filled with either air, olive oil, transformer oil, acetone, or distilled water and sealed with copper tape. The experimental results demonstrate that the proposed antenna can be configured to operate in the 3.25 to 3.52 GHz and 4.5 to 5.04 GHz bands. The proposed SDA is designed and fabricated on a substrate of 1.575 mm thick Rogers 5880 ( = 2.2 and tan δ = 0.0009). It is observed that frequency shift is more when using higher permittivity fluids. The proposed antenna model has competitive features such as simple design, compact size (), better isolation (>30 dB), and fine-tuning, which makes it suitable for modern multiband and multifunctional gadgets. The simulated and measured circuit responses are in good agreement.

Design of Miniaturised Circular Polarisation-Reconfigurable and Frequency Agile Slow-Wave SIW Based Microstrip Antenna for Wireless Applications

ABSTRACT Maintaining acceptable radiation performance over the entire operation bandwidth is a significant challenge in development of a miniaturized reconfigurable antenna To address this issue, a new Substrate Integrated Waveguide (SIW) based reconfigurable antenna using slow wave structure is presented in this study. The proposed SIW antenna is based on a layered construction with metallic blind vias connecting to ground plane of SIW. The multi-layer structure of SIW with blind vias helps to separate magnetic and electric fields in the SIW cavity. Thus, a slow wave effect is also utilized and it leads to 36% reduction in the antenna size as compared to conventional SIW cavity. To attain the polarization and frequency reconfiguration, a cross slot is introduced in the top metallic layer of the SIW cavity and four PIN diodes are connected into the cross-slot arms. Experimental results exhibit frequency reconfigurability in different operating regions with resonant frequencies 4.35, 5, 5.8, 6.4, and 9.6 GHz. The polarization reconfigurability of the proposed antenna is achieved at 5 GHz with LP/RHCP/LHCP. The proposed antenna exhibits 3-dB axial ratio bandwidth of 4.8 to 5.2 GHz with peak gain of 4.2 dBi.

Induction-Diffusion-Adsorption Process of Malachite Green for Cobalt Superconformal Electrodeposition

Cyclic voltammetry (CV), chronopotentiometry and quartz crystal microbalance were used to study the effect of Malachite Green (MG) on bottom-up growth of cobalt. The addition of MG not only inhibited the reduction of Co2+ but also accelerated the hydrogen evolution process. The metal reduction process was enhanced as well as the current efficiency was higher with the increase of pH. The bottom-up growth of cobalt can be achieved with the potential of −1.20 V. Induction-diffusion-adsorption superconformal electrodeposition mechanism was proposed to illustrate the synergistic effect of MG and pH on the growth of cobalt. On one hand, the MG concentration gradient and pH gradient could be formed to achieve a growth rate difference within blind vias so as to obtain bottom-up growth (diffusion-adsorption effect). On the other hand, the growth rate difference was intensified due to the accelerating effect of MG on HER so as to boost the cobalt superfilling (induction effect).

Miniaturized Quad-Band Filter Design Using Substrate Integrated Coaxial Cavity

We propose a miniaturized quad-band filter (QBF), designed using substrate-integrated coaxial cavities (SICCs). The employed SICC structure consists of two vertically stacked substrates with a large circular patch embedded in between. The embedded patch is segmented unevenly into four pieces, which are shorted to the cavity's bottom wall through one or two blind vias. This SICC structure exhibits four independently controlled resonances with frequencies much lower than the frequency of its conventional SIW cavity counterpart, thus achieving size reduction. A sample quad-band filter is designed and fabricated for experimental measurement. Reasonably good agreement between measured and simulated data is observed.

A Compact-Size and High-Efficiency Cage Antenna for 2.4-GHz WLAN Access Points

In this communication, a compact-size and high-efficiency air cavity antenna with a cage-like structure is proposed for 2.4 GHz wireless local area networks (WLAN). The air cavity antenna is constructed with four sides of hybrid metallized vias, including sparsely arranged blind vias and tightly arranged shorting vias. First, the antenna size is significantly reduced by utilizing the shorting vias, which makes the antenna operate at the high-order TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {1/2,1/2}}$ </tex-math></inline-formula> mode. Then, by loading the capacitive blind vias at the radiating apertures, the antenna size is further miniaturized. Notably, high radiation efficiency is obtained attributed to the lower dielectric loss of the air-medium structure. Finally, a prototype of the proposed cage antenna has been fabricated and tested with good agreement between simulated and measured results. In such a compact size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.128\lambda _{0} \times 0.128 \lambda _{0} \times 0.10 \lambda _{0}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> is the free-space wavelength at the center frequency), the measured total efficiency over 90% is achieved in the WLAN band by the cage structure. Compared with the existing 2.4 GHz antennas, the proposed one is with the ascendency of compact size and high radiating efficiency for WLAN applications.

Design of SIW based Frequency Reconfigurable Antenna for K/Ku band applications

A frequency reconfigurable antenna based on substrate integrated waveguide (SIW) technology is proposed in this paper for K/Ku band applications. In most of the previous reconfigurable structures terminal SIW was used but here in this proposed structure, terminal as well as the blind vias is being implanted to achieve maximum reconfigurability and better efficiency of the miniature antenna. The antenna parameters are analysed thoroughly without diode as well as with diode. According to the measurements, the suggested antenna has an impedance bandwidth of 12 to 12.8 GHz in off condition and in addition to this from 22 to 22.8 GHz in ON condition with a peak gain of 7.5 dB. The radiation efficiency of proposed work is 90%.

Influence of suppressing additive malachite green on superconformal cobalt electrodeposition

• Adsorption-coordination mechanism was calculated by quantum chemistry to demonstrate the inhibition effect of MG. • Adsorption-transport mechanism was illustrated to explain the bottom-up growth of cobalt under the influence of MG. • The nucleation and growth of cobalt is 3D diffusion-controlled progressive nucleation process. A novel suppressor, malachite green, was used to achieve bottom-up growth of cobalt in this work. Electrostatic potential, HOMO/LUMO of malachite green was calculated to provide an insight into the interaction between malachite green and metal substrate, while charge distribution, AIM (atoms in molecules theory) analysis and IRI (interaction region indicator) analysis were coupled to analyze the interaction between malachite green and cobalt ions. Adsorption-coordination inhibition mechanism was illustrated to explain the inhibition effect of malachite green. Electrochemical analysis was applied to evaluate malachite green. Cyclic voltammetry was used to confirm the inhibition effect of malachite green, while EQCM analysis demonstrates that the current efficiency was lowered by MG. The nucleation and growth of cobalt is 3D diffusion-controlled progressive nucleation growth under the influence of hydrogen evolution reaction and the compact cobalt coatings could be obtained by surface analysis. The effective MG concentration gradient could be formed within blind vias according to current transient analysis so as to develop electroplating rate difference. The bottom-up growth of cobalt within blind vias was achieved by carrying out electroplating test and the adsorption-transport mechanism was proposed to explain the superconformal electrodeposition of cobalt under the influence of MG.

The effects of pressure, temperature, and depth/diameter ratio on the microvia filling performance of Ag-coated Cu micro-nanoparticles for advanced electronic packaging

ABSTRACT Conductive fillers made from metal nanoparticles offer many advantages for the fabrication of a variety of electronic devices, but when they have a porous structure, their poor conductivity limits their adoption in many applications. In this study, an Ag-coated Cu micro-nanoparticle paste is used to achieve compact filling of blind vias on flexible copper clad polyimide laminates through a multistep filling and sintering technique. The filled blind vias achieve a resistivity as low as 6.2 μΩ·cm, which is comparable that of electroplated blind vias. Higher sintering pressure and temperature promote the filling performance, while the conductivity deteriorates at a via depth/diameter ratio greater than 1:1. Finite element simulations reveal a stress inhomogeneity in vias with large depth/diameter ratios, which is the key to understanding the evolution of the conductive properties of a paste-filled via. This study provides an effective method for high-performance microvia filling as well as insights into the mechanism that influences its performance.

Ablation behavior of a network interlacing ZrC-VC ceramic coating prepared by a pioneering spillover permeation

A novel network interlacing ZrC-VC ceramic coating was prepared by a pioneering spillover permeation. With the increase of Zr content in the blind vias, the content of ZrC in the coating and the density of the coating all decrease. The density of the coating on C/C–ZrC–SiC substrate is obviously higher than that on C/C substrate. The linear ablation rate of the novel ceramic coated C/C–ZrC–SiC composites was −0.06 μm/s with about 20 and 1.56 times reduction than C/C composites and C/C–ZrC–SiC composites respectively. The improved ablation resistance was attributed to a dense honeycomb ZrO2 layer filled with liquid vanadium oxide in the ablation center and the improved thermal radiation.

An active microfluidic sensor based on slow-wave substrate integrated waveguide for measuring complex permittivity of liquids

In this paper, a microfluidic sensor based on slow-wave substrate integrated waveguide (SW-SIW) is proposed to measure the complex permittivity of liquids and it achieves an ultrahigh quality factor of 51156, which is much higher than previous reported designs. The proposed sensor consists of three-layer dielectric substrates and an active circuit. The traditional SIW has the fundamental mode of TE101, whose electric field is concentrated inside the SIW structure. The SW-SIW, which is evolved from traditional SIW structure, has the characteristic of relatively small electrical size due to large equivalent capacitance and the capability to confine the electrical field density further. The internal rows of blind via holes are connecting the top layer of second substrate to the bottom layer of third substrate. In order to further reduce the electrical size, an air cavity is formed in second substrate around blind via holes as it can increase the equivalent capacitance of SW-SIW resonator. The air cavity has an important impact on the resonant frequency of the sensor, and the electrical size could be reduced by enlarging the air cavity. In this paper, an appropriate air cavity is adopted with comprehensive consideration of detection sensitivity and electrical size. The polydimethylsiloxane (PDMS) microfluidic substrate is embedded in first substrate. When the resonator is excited, the electric field is confined above the surface of blind vias. The electric field varies with the volume fraction of aqueous solution injected into the microfluidic channel, and the resonant frequency and quality factor alter correspondingly. The variations in the resonant frequency and quality factor are applied to retrieve the complex permittivity of liquid samples. The proposed sensor is fabricated and tested, it has a dimension of 0.678λ0 × 0.432λ0 (λ0 is the wavelength in free space at 3.7 GHz), and the peak sensitivity and unloaded quality factor are about 2.5 % and 51156, which are improved by 67 % and 5015 % than traditional SIW sensor, respectively. In particular, the sensitivity of measuring loss tangent of liquid sample is improved by several times to hundreds of times with the loss tangent range from 0.1 to 0.9 than other reported sensors. The measured data has a good agreement with the reference complex permittivity.

A miniaturized mm‐wave leaky wave antenna based on CRLH slow‐wave SIW for symmetric wide angle beam scanning

In this article, a novel miniaturized wide beam scanning range multi-layered mm-wave leaky-wave antenna (LWA) based on slow-wave (SW) substrate-integrated waveguide (SIW) is presented. The SW effect is introduced by loading conventional SIW with internal metalized blind vias connected to the bottom ground plane. The SW effect in the SIW structure causes the separation of the electric and magnetic field components in the structure which leads to the reduction in lateral dimensions of the proposed topology by 35% as compared to the conventional SIW. The proposed LWA exhibits a miniaturized volume of 6.6 × 0.41 × .07 λ3. The radiation in the proposed design is realized by introducing U-shaped slots in the unit cell of the SW-SIW structure. Experimental results show that the proposed SW-SIW LWA achieves almost symmetric and continuous beam scanning from −48° to 52° including the broadside direction within the impedance bandwidth of 23.7–28.1 GHz. The proposed antenna achieves a peak gain of 14.52 dBi and the half-power beamwidth of LWA is as low as 10°. The proposed antenna also exhibits radiation efficiency of above 90% within the bandwidth. The proposed design can be a potential candidate for mm-wave frequency beam scanning applications.

Integral Plugged Blind via in Printed Wiring Boards

Adoption of fine pitch and high lead count area array components in high-reliability applications such as military and space electronics demands high-density interconnect (HDI) features in multilayer printed wiring boards (PWBs). Usage of cap-plated fine vias that are plugged with dielectric material is one of the approaches to meet the circuit density requirements. In this article, a novel method called &#x201C;integral plugged blind via&#x201D; without secondary processing steps, such as curing and planarization, is described to realize HDI multilayer PWBs. In this method, through vias are epoxy plugged during the lamination of inner layer circuits in vacuum-assisted hydraulic press cycle. Plugged blind vias are formed as an integral part of the fabrication process. It is observed that there is no excess ooze out of resin material from the blind vias in the laminated substrate and blind vias are found to have a negligible dimple and no voids. This is attributed to the gasket effect due to the elastomeric property of specialty release films, which conform (follow) to the contour of plated through vias during the vacuum lamination cycle. Plugged blind vias are subjected to critical thermomechanical stress to evaluate interconnection integrity. It is found that there is negligible change in the resistance of vias and resin plugged vias are free from defects such as barrel crack or knee crack of plated through hole (PTH) or delamination in the cured plugged material. Robustness of these resin-filled blind vias is attributed to anchored plated barrel with the additional support provided by plugged material, which restricts the thermomechanical deformation of plated copper.

Ultra-Low-Profile Continuous Transverse Stub Array for SatCom Applications

Modern K-/Ka-band satellite communications have become increasingly demanding in recent years with regard to the performance of the terminal antenna used in the link. These terminals should be high gain and broadband, as well as guarantee polarization diversity over a large field of view. A low profile is also highly desired to integrate the antenna system into a variety of moving platforms, such as aircraft and trains. An ultra-low-profile continuous transverse stub array is proposed here to tackle these challenges. The antenna array is realized in printed circuit board technology by adopting a contactless transition between the stacked-up layers without resorting to blind or buried vias. The proposed antenna is wideband (impedance matched within the 19–31 GHz band, i.e., ~50%) and provides multibeam radiation for polar angles as far as ±22.5°. The peak value of the gain is 19.7 dBi, and the maximum radiation efficiency equals 50%. Furthermore, the antenna array is combined with a dual-band polarization converter. The latter provides orthogonal circular polarization (CP) in two non-adjacent bands. The overall antenna system performs right- and left-hand CPs within the SatCom downlink and uplink in the K-/Ka-band, respectively. For each polarization, the axial ratio is below 3 dB over 9.47% and 4.42% fractional bandwidths, respectively.

Photo curable resin for 3D printed conductive structures

In this study, a new resin formulation method was developed to fabricate 3D printed conductive structures via digital light processing (DLP) 3D printing technology. Metal fillers, such as silver-coated copper flakes (AgCu) and silver nanoparticles (AgNP), were tested for conductive resin formulation. With low UV shielding and printing derivation, AgCu was selected as the conductive filler, and mixed with a photo curable acrylic resin. To resolve the sedimentation problem of metal fillers, carbon nanotubes (CNT) were added as a thickening agent to provide a supportive network to stop the metal fillers from settling. With the CNT addition, AgCu up to 70 wt% can be well dispersed in the acrylic resin with both fluidity and suspension stability. The resin can be printed into 3D metal circuitry structures with a conductivity up to 1000 S/cm without sintering. Multi-material stereolithography was also performed to produce conductive circuitry within insulation materials. The sectional view showed great connections between multiple layers of printed conductive tracks. Through-hole vias and blind vias were also built with great quality to demonstrate the capability of this conductive resin formulation.

Miniaturized Band Pass Filter Design Using Half Mode Substrate Integrated Coaxial Resonators.

The contribution of this work is to propose a half-mode substrate integrated coaxial resonator (HMSICR) and its application in bandpass filter (BPF) design. The proposed HMSICR is formed by evenly bisecting a square substrate integrated coaxial resonator (SICR), which is a cavity composed of two dielectric substrates and three metal layers. The SICR’s sidewalls are mimicked by periodically spaced thru-via arrays, and a circular patch is embedded in the middle metal layer of the SICR with the patch shorted to the cavity’s bottom wall by a circular array of blind vias. This HMSICR can drastically lower the cavity’s resonance frequency. The achieved frequency reduction rate of the proposed HMSICR, as compared with that of its conventional substrate integrated waveguide (SIW) cavity counterpart, reaches 70%. A sample four-HMSICR BPF is built for the circuit verification measurement. To further reduce the sample filter’s area, the composing HMSICRs are vertically stacked in a back-to-back configuration. We believe that its obtained size-reduction rate reaches the highest record.

A Low-Loss Broadband Planar Transition From Ground Coplanar Waveguide to Substrate-Integrated Coaxial Line

In this letter, a three-dimensional ground coplanar waveguide (3D-GCPW) structure is proposed as a broadband planar transition between the conventional GCPW and substrate integrated coaxial line (SICL). The proposed 3D-GCPW contains a 3-D central conductor constructed by two copper layers which are connected together by metallized blind vias and two side ground planes. Its characteristic impedance is mainly determined by the width of the 3-D central conductor and the gap to the side ground plane; thus, the requirement for machining accuracy of metallized blind vias in 3D-GCPW can be reduced during the machining process. A back-to-back structure of the 3D-GCPW transition is fabricated by a multilayer printed circuit board (PCB) process and measured to validate the good performance. The experimental results show that the proposed 3D-GCPW transition exhibits a reflection coefficient less than −10 dB and an acceptable insertion loss within dc to 42 GHz, making it promising for high-performance multiple-channel transceiver or massive integrated applications.

A Wideband Millimeter-Wave Rotman Lens Multibeam Array Using Substrate Integrated Coaxial Line (SICL) Technology

This article presents a wideband Rotman lens multibeam array implemented with substrate integrated coaxial lines (SICLs) for millimeter-wave (mmW) applications. Unlike other dispersive transmission lines commonly used with printed circuit boards, SICL is a nondispersive planar coaxial line that supports the propagation of transverse electromagnetic waves, thus enabling broadband designs of mmW Rotman lenses. Two types of wideband, compact transition structures consisting of small strips and blind vias were designed to transfer energy between the input–output SICLs and parallel-plate lens cavity. Wideband tapered slot antennas excited by SICLs, with a compact lateral size and wide beamwidths, were introduced as the radiating elements to realize a wide scanning range over a large bandwidth. For a proof-of-concept demonstration, a multibeam array prototype that includes seven beam ports and ten array ports connected to ten antenna elements was designed and fabricated. Experimental results agree well with simulation results and show that the proposed multibeam array has an overall bandwidth of 57% (25–45 GHz) with nearly frequency-invariant beam steering performance within ±45°. The desirable wideband operation in conjunction with the ease of integration with planar circuits and low-cost fabrication make the proposed multibeam array design a promising solution for various mmW applications.