Search

Mechanical property changes in friction stir welding can directly affect the rebalance of the stress field in friction stir welding. This means that it reveals a high relevance with the residual states of friction stir welding. Here, we propose a subregion model in which the mechanical property changes are considered to predict the residual states in friction stir welding of dissimilar metals. Results indicate that the accuracy of the predicted distortion can be greatly increased when the different mechanical properties are considered in friction stir welding of 2024-T3 and 6061-T6. The final mechanical property is determined by the mixture of the materials at retreating and advancing sides. The final mechanical property in the stirring zone can be increased to 171 MPa for yield strength and 194 MPa for tensile strength when the strength of the advancing side material is higher. The shrinkage of material in the stirring zone during the cooling stage is the key reason for the formation of the tensile residual stress and the V-shape distortion on the cross-section in the as-weld state. [ABSTRACT FROM AUTHOR]

Glass has been shown to be a capable core substrate material for high-frequency applications. In this article, we examine the capabilities of ultra-thin glass as a material that can be used for high-frequency flexible applications. The two stack-ups discussed in the work presented are 60 $\mu \text{m}$ in total thickness with a core glass substrate (Schott AF32) of 30 $\mu \text{m}$ thickness. One stack-up uses 15 $\mu \text{m}$ JSR GT-N01 as a buildup dielectric on each side of the glass and the other uses 15 $\mu \text{m}$ Taiyo Ink photo imageable dielectric (PID). Both stack-ups have been characterized to 110 GHz and have shown to have comparable performance to materials used in this frequency range. This work then focuses on the mechanical characterization of these stack-ups using free arc bending. The free arc bending tests show that both ultra-thin glass stack-ups are suitable for bending applications as the tested samples can bend to a panel separation below 33% of the sample’s total length. This article concludes that the ultra-thin glass stack-ups are suitable for high-frequency flexible applications because the electrical performance is comparable to other high-frequency rigid materials while exhibiting their flexible capabilities. [ABSTRACT FROM AUTHOR]

A recently developed material technology at Corning Inc., namely, Alumina Ribbon Ceramic (ARC), is investigated as a potential substrate candidate for fifth generation (5G) and millimeter-wave (mm-wave) applications. In this article, we characterize an 80- $\mu \text{m}$ -thick ARC substrate material in the frequency range of 3–50 GHz using microstrip ring resonator (MRR) method and extract the loss of various planar transmission lines, such as microstrip and coplanar waveguide (CPW) lines on ARC substrate up to 50 GHz as well. Moreover, different test structures designed on an 80- $\mu \text{m}$ -thick ARC substrate are utilized to extract the electrical parasitics associated with a single-grounded through-alumina via (TAV) and transmission properties of ground–signal–ground (GSG) TAV of 40 $\mu \text{m}$ diameter over the frequency range of 0.1–50 GHz. The semiadditive patterning (SAP) process is employed to metallize the top and bottom layers of ARC substrate to form the copper traces for the designed structures. Combined with the previous characterization results of a 40- $\mu \text{m}$ -thick ARC substrate in 30–170 GHz, the dielectric constant of ARC was extracted to be ~10.12 over 3–170 GHz, while its loss tangent varies in the range of $6.6\times 10^{-5}-1.3\times 10^{-3}$ over the same frequency band. The average measured insertion loss of CPW lines varied from 0.026 to 0.24 dB/mm over 3–170 GHz. For the microstrip lines, the average measured insertion loss over the same frequency range was extracted to be between 0.019 and 0.293 dB/mm. Furthermore, the parasitic inductance and resistance of a single-grounded TAV are extracted to be 24.41 pH and $0.987~\Omega $ , respectively, at 50 GHz, and the insertion loss per a GSG-TAV extracted from CPW-TAV daisy chain measurements is found to be 0.056 dB at 50 GHz as well. In addition to an excellent performance of ARC-based interconnects, the TAV in ARC is shown to have lower transmission loss up to 50 GHz, while exhibiting low parasitics. [ABSTRACT FROM AUTHOR]

This study, to the best of authors’ knowledge, is the first to investigate the feasibility of using picosecond UV laser ablation to fabricate ultrasmall microvias scaled down to 3 $\mu \text{m}$ and less with a pitch of 8 $\mu \text{m}$ in a 5- $\mu \text{m}$ Ajinomoto buildup film (ABF). The state-of-the-art microvias are 20 $\mu \text{m}$ in diameter by a nanosecond UV laser and 5 $\mu \text{m}$ in diameter by a picosecond UV laser reported in our previous study, but microvias of less than 2 $\mu \text{m}$ in diameter are needed to meet IO density requirements for today and future’s high-bandwidth packaging and heterogeneous system integration. In this study, we have investigated the impact of laser power, beam sizes, and materials on the via size and explored the feasibility of picosecond UV laser ablation for ultrasmall microvias with an additional layer of 80-nm-thick copper on top of the dielectric as a barrier layer. The power used to fabricate the 5- $\mu \text{m}$ microvias in a 5- $\mu \text{m}$ -thick ABF could open 2- $\mu \text{m}$ holes in the copper barrier layer due to the higher ablation threshold of copper. The drilled copper layer then serves as a mask to produce smaller microvias in the dielectric layer beneath the copper. In this article, fully opened microvias of 3 $\mu \text{m}$ diameter in ABF will be demonstrated. Submicrometer openings in copper are also achieved, which suggests the feasibility to scale down via diameter to submicrometer level. [ABSTRACT FROM AUTHOR]

This article presents the modeling, development, and demonstration of glass interposer technology with single-mode waveguides (SMWGs) for high-bandwidth communications and embedded trenches for ultrafine copper traces for high-speed electronics. Glass as the substrate for the integration of photonics and electronics exhibits a unique combination of superior properties over silicon, laminates, and polymers. In conjunction with the advantages of glass, shape control of photoimageable dielectric lines during development and cure was developed and optimized. Single-mode polymer waveguides on glass were fabricated and characterized. Sample preparation methods and their impact on the sample edge quality and coupling loss will also be discussed in this article. Overall, this article presents the successful process development and demonstration of 3- $\mu \text{m}$ embedded trenches in the dielectric film for ultrafine copper traces and 2- $\mu \text{m}$ microvias for interlayer interconnects. [ABSTRACT FROM AUTHOR]

This article presents for the first time microvias scaled down to sub- $5~\mu \text{m}$ in diameter fabricated using picosecond UV laser ablation in a nonphotoimageable dielectric film. The motivation of this article is to address post-Moore and More-than-Moore packaging interconnect needs. Microvias play a critical role in package interconnections in IO density and the IC bump pitch for 2.5-D interposers and fan-out packages. UV laser ablation has been the key technology for fabricating small microvias in high density interconnect (HDI) packaging for more than two decades. The state-of-the-art microvia fabricated by UV laser ablation is still at $20~\mu \text{m}$ in diameter and 50 $\mu \text{m}$ in pitch. This article explores the feasibility of fabricating microvias of $5~\mu \text{m}$ or less in diameter with a commercially available picosecond UV laser system. The experimental results show that microvias of $5~\mu \text{m}$ or less in diameter in a 5- $\mu \text{m}$ -thick Ajinomoto buildup dielectric film (ABF) are achieved. This article also addresses the fundamentals of picosecond pulsed laser ablation on polymer dielectric materials and processes optimization to generate sub-5- $\mu \text{m}$ microvias. The via pitch of 8– $12~\mu \text{m}$ is demonstrated. UV laser ablation also addresses the issue of limited availability of photosensitive dielectric materials for photolithography-based microvia fabrication. [ABSTRACT FROM AUTHOR]

This paper presents the latest advances in photolithography technologies to enable scaling of package redistribution layer (RDL) toward critical dimensions (CD) of $1 ~\mu \text{m}$ and below. High-bandwidth memory channels require not only fine pitch but also low-trace-delay RDL. High-aspect-ratio (AR) traces enable lower delays, and the photolithographic advances to achieve such traces are demonstrated on panel-based glass substrates for packages with low cost, high input/output (I/O) density, high bandwidth, and large body size. CD of 0.9- $\mu \text{m}$ line and space with an AR of 5.5 was successfully demonstrated using a low-numerical aperture (NA = 0.16) $1 \times$ i-line projection stepper tool with a novel chemically amplified plating photoresist. The 1- $\mu \text{m}$ lithography technology is a must for high-density RDL to enable 2.5-D interposer and embedded fan-out package substrates. These architectures can achieve I/O densities of 500 IOs/mm/layer. The resistance of the trace with an AR of 5 is five times lower than a trace with an AR of 1. This technological advance will greatly reduce the signal propagation loss and increase the data rate of the RDL traces. The combination of high density and high data rate will greatly increase the system interconnect bandwidth. Furthermore, low-NA stepper with a large exposure area will enable the fabrication of large-body-size interposers at low cost. This paper analyzes the relationship between trace width resolution ($w$), depth of focus, and materials to conclude that it is feasible to fill the gap between semiconductor back-end-of-line and package substrate RDL technologies. The final section discusses the issues in process development of lithography for multilayer fine-line RDLs. [ABSTRACT FROM AUTHOR]

This paper presents a novel organic embedded trace damascene redistribution layer (RDL) process for panel-scale 2.5-D interposers and high-density fan-out package (HDFO) substrates. A minimum feature size of 1.5- \mu \textm line and space using ultrathin polymer dielectrics on glass, silicon, and as well as on organic laminate was demonstrated. This is the first demonstration of a complete set of materials and processes that can be applied to large glass or organic panels, to bridge the interconnect gap between current semiadditive process (SAP) RDL and wafer back-end-of-line (BEOL) RDL. The ultra-fine pitch multilayer RDL structures demonstrated in this paper achieve an optimum balance of high IO density, high electrical performance, and low process costs. IO density in terms of IOs per mm per layer, as defined by Intel, refers to the number of traces routed per millimeter of die edge on one RDL layer of an interposer or package substrate. The current SAP technology can achieve an IO density of about 40 IOs/mm/layer on 510 mm $\times \,\, 510$ mm organic laminate panels. The challenges of fabricating copper metal traces below 5 20~\mu \text{m} or less; 3) high AR of routing traces in the range of 2–4; 4) precise RDL linewidth control; 5) double-sided process with glass core; and 6) reduced number of process steps and panel-scalability leading to lower fabrication costs. [ABSTRACT FROM PUBLISHER]

Package-integrated and ultra-thin low-pass filter (LPF) and bandpass filter (BPF) with footprint smaller than $0.5\lambda _{0}\times 0.5\lambda _{0}\times 0.025\lambda _{0}$ at the operating frequencies of 28- and 39-GHz bands are presented for 5G and mm-wave small-cell application. Such package integration of 5G filters with ultrashort 3-D interconnects allows for low interconnect losses that are similar to that of on-chip filters, but low component insertion loss of off-chip discrete filters. These thin-film filters exhibit a cross-sectional height of $188.5~\mu \text{m}$ and can be utilized either as embedded components or integrated passive devices in module packages. Three topologies of LPF and BPF in total are modeled, designed, and fabricated on precision thin-film buildup layers on glass substrate as a core. Large-area panel-compatible semiadditive patterning (SAP) process is utilized to form high-precision topologies to aid the low-cost fabrication of ultraminiaturized filters. SAP also enables the realization of ultra-thin traces to precisely model high-impedance inductive lines compared to conventional subtractive etching and printing techniques. This results in filters with low insertion loss, low VSWR, and high selectivity. The simulated and measured results of filters show an excellent correlation. [ABSTRACT FROM AUTHOR]

This paper presents the latest advances in extending semiadditive process (SAP) methods to 2–5 \mu \textm lines and spaces, achieved using dry film photoresists on thin glass substrates, toward meeting the routing requirements for 20- \mu \textm bump pitch interposers. High-density chip-to-chip interconnections on 2.5-D interposers are a key enabler to meet the high logic to memory bandwidth needs of next-generation electronic systems. Such 2.5-D interposers require ultrafine redistribution layer (RDL) traces with line widths and spacing below 5~\mu \textm . This paper reports on the extension of panel scale and lower cost SAPs to achieve less than 5~\mu \textm lines and spaces, based on the ultrasmooth surface and improved dimensional stability of thin glass panels. A modified low-cost SAP method with newly developed differential seed layer etching was employed to fabricate the fine line and space patterns and coplanar waveguide (CPW) transmission on thin glass panels. Fine lines down to 2- \mu \textm lines and spaces and CPW lines with signal lengths up to 5 mm and ground-to-signal gaps down to 5.5~\mu \textm at 15- \mu \textm signal widths were successfully fabricated on ultra-thin glass panels. For comparison, the same processes were also applied to a silicon wafer. The signal insertion losses of CPW lines on the glass were 0.024 dB/mm better at 15 GHz than those on the silicon, as confirmed by simulations as well as VNA measurements. The measured insertion loss of 5-mm long CPW lines on glass interposer was 0.7 dB at 10 GHz and matched well to the simulated values. [ABSTRACT FROM PUBLISHER]

This paper presents the design, analysis, and demonstration of an ultra-thin wireless local area network (WLAN) RF receiver module with chip-last embedded actives and embedded passives in a low-loss organic substrate using system-on-package approach. The overall thickness of the module, including the embedded dies, is \(160~\mu \) m- more than \(3\times \) thickness reduction compared to current wire-bond and flip-chip packages. The receiver module consists of gallium arsenide low-noise amplifier (LNA) dies, chip-last embedded in an ultrathin, low-loss organic substrate, and connected to a substrate-embedded three-metal-layer band-pass filter (BPF) in close proximity. Full-wave electromagnetic simulation was performed on a 3-D model of the designed receiver module to obtain its two-port scattering parameters (S-parameters) and to study noise coupling between the power-supply network and the signal path. The receiver module was then fabricated, tested for yield of the BPF, assembled and characterized, and the measured results were correlated with simulation. The BPF dimensions in the package were \(1.5~{\rm mm} \times 2.9~{\rm mm} \times 0.15~{\rm mm}\) , and its measured pass-band insertion loss was 2.3 dB with more than 15 dB return loss. The receiver module (LNA + BPF) dimensions were \(5.5~{\rm mm} \times 2~{\rm mm} \times 0.16~{\rm mm}\) , and it had a measured peak gain of 11 dB with more than 30 dB attenuation in the adjacent-band, indicating excellent performance in a miniaturized form-factor. [ABSTRACT FROM AUTHOR]

The trend toward miniaturization of electronic systems demands reliable small fine-pitch through vias in organic packages and high-density interconnect system boards. Fine-pitch through vias in glass fiber-reinforced organic packages suffer from electrical insulation failures due to the formation of conductive anodic filaments (CAFs) in the presence of temperature, humidity, and voltage. In addition to the requirement for fine-pitch through vias, restriction in use of halogens as well as the move toward green electronic systems has driven the development of halogen-free thermally stable novel resin formulations for next-generation glass fiber-reinforced substrates. The introduction of new resin chemistries can also affect the reliability, as CAF failures are known to depend on the substrate material properties. In this paper, CAF reliability of small and fine-pitch through vias in a halogen-free glass fiber-reinforced organic substrate is investigated. Test structures with through via diameter of 100 \mum with two different pitches, i.e., 250 and 500 \mum, were fabricated and tested using 100 V direct current (dc) bias at 85^\circC and 85% relative humidity for 1000 h. Insulation failures were observed in test structures with a pitch of 250 \mum, while the test structures with a pitch of 500 \mum exhibited stable insulation resistance during the test. Failures were identified using optical microscopy and characterized using scanning electron microscopy. The results indicate that CAF failures are a concern with fine-pitch through vias in packages, and, therefore, careful selection of materials and processes is required for achieving reliable fine-pitch through vias in high-density packages. [ABSTRACT FROM AUTHOR]

Rapid changes in the semiconductor industry will continue toward higher functionality that leads to higher input/outputs (I/O) counts, pushing packaging towards higher density architectures. In the next two to three years, the I/O pitch will fall within 100 \mum for area array die and 30 \mum for periphery die. That raises an important question to the packaging industry: How will the rapid shrinkage of the I/O pitch affect the package substrate for chip attaching? The answer is sub-10 micron copper line technology. Theoretical and experimental studies on the limitations of using mercury i-line ultraviolet photolithography have been carried at the Packaging Research Center at Georgia Tech. Furthermore, ultra fine copper line routing substrates are demonstrated for flip chip attaching by using semi-additive metallization process. [ABSTRACT FROM AUTHOR]

As microsystems continue to move toward higher speed and microminiaturization, the demand for interconnection density both on the IC and the package levels increases tremendously. The 2002 ITRS roadmap update identifies the need for sub-100-pm area array. pitch and data rates of 10 Gb/s in the package or board by the year 2010, requiring much finer lines and vias than the current microvias of 50 pm diameter and lines and spaces of 25 μm. After a brief description of the future need for high-density substrates, the historical evolution of microvia technologies worldwide is summarized. With the move toward highly integrated and higher performance system-on-a-package (SOP) technology, the demand for microvia wiring density in the package is increasing dramatically requiring new innovations in fine line, Wtralowloss, and ultrathin-flim dielectrics. The low-cost needs of this technology are driving research in high throughput and large area processes in dielectric and conductor deposition. The third section of this paper describes in detail some of the key emerging global microvia research and development in the fabrication of microminiaturized, multifunction SOP packages including rapid curing of low-loss dielectric thin films on organic substrates, environmentally friendly high-speed electroless copper plating, ultrafine lines, and spaces down to S pm and low-cost stacked via structures without chemical-mechanical polishing. This paper concludes with a perspective on future directions in dielectrics and conductor materials and processes leading to ultrahigh-density and low-cost microvia technologies for build-up SOP implementation. [ABSTRACT FROM AUTHOR]

A series of novel polymers (coded as BCT‐1 to BCT‐6 (BTC is block triphenylamine)) based on N1‐(4‐aminophenyl)‐N1‐phenyl benzene‐1,4‐diamine, pyridine‐2,6‐dicarboxylic acid, 4,4′‐(phenyl azanediyl)dibenzoic acid (PDA), and different diamine compounds were synthesized successfully through a polymer condensation reaction. For comparison, model polymers, BCT–2,6‐pyridine dicarboxylic acid (PA) and BCT–PDA, were synthesized as well. The electrochromic properties of the BCTs were determined via an electrochemical workstation and a UV–visible spectrophotometer. Through electrooxidation, the polymer films showed reversible redox processes and steady color changes. In a comparision of the electrochromic characteristics of the BCTs, almost all the novel polymer films showed a better electrochromism stability, a higher electrochromic coloration efficiency (CE), and a more rapid switching time than BCT–PA and BCT–PDA. Among these polymers, BCT‐1 exhibited the highest CE of 266.7 cm2/C, and BCT‐4 showed the most rapid switching time (color switching time = 3.08 s and bleaching time = 2.01 s). © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47264. [ABSTRACT FROM AUTHOR]

High-frequency, high-power picosecond lasers have important and wide-ranging applications in laser ranging, optoelectronic countermeasures, and ultrafine industrial processing. Pulse compression based on stimulated Brillouin scattering (SBS) can achieve a highly efficient picosecond laser output, while improving the peak power and beam quality of the laser. In this paper, a generator-amplifier two-cell structure with frequency-detuning was proposed to achieve a pulse output that combines high compression ratio and high energy reflectivity. The experiment proved that under a pump pulse width of 15 ns and repetition frequency of 10 Hz, when the generator cell and amplifier cell media were selected as HT-230, the highest energy reflectivity of 46% and narrowest compression pulse width of 1.1 ns were achieved, and the pulse compression ratio was 13.6. When the amplifier cell was selected as FC-770 and the generator cell was selected as HT-230, an energy reflectivity of 52% and a compression pulse width of 840 ps could be achieved simultaneously, and the pulse compression ratio was 18.

We introduce here a simple method of integrating 45 degrees total internal reflection micro-mirrors with polymer optical waveguides by an improved tilted beam photolithography on printed circuit boards to provide surface normal light coupling between waveguides and optoelectronic devices for optical interconnects. De-ionized water is used to couple ultraviolet beam through the waveguide core polymer layer at 45 degrees angle during the photo exposure process. This technique is compatible with PCB manufacturing facility and suitable to large panel board-level manufacturing. The mirror slope is controlled accurately (within +/- 1 degrees) with high repeatability. The insertion loss of an uncoated micro-mirror is measured to be 1.6 dB.