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In the current study, the effects of flat sweeping frequency and pulsed ultrasound (FSFPU) application with different frequency modes on the inactivation of polyphenol oxidase (PPO) in strawberry juice were investigated in the temperature range of 40–60 °C. The sweeping frequency modes employed includes single-frequency modes of 22 ± 1, 40 ± 1 kHz, and dual-frequency of 22 ± 1 and 40 ± 1 kHz in simultaneous modes. Results suggested that the inactivation patterns of PPO in strawberry juice all followed the first-order kinetic model (R2 = 0.965–0.997). The D values of PPO during thermal inactivation at 40–60 °C were in the range of 126.5–22.8 min, respectively. Remarkable decreases of the D values of PPO can be observed under the different ultrasound frequency modes. They were 100.1–20.3 min (22 ± 1 kHz), 73.3–18.6 min (40 ± 1 kHz), and 56.9–14.5 min (22/40 ± 1 kHz). The activation energy (Ea) during thermal inactivation was 77.25 kJ/mol, which decreased to 73.65 kJ/mol (22 ± 1 kHz), 62.86 kJ/mol (40 ± 1 kHz), and 60.17 kJ/mol (22/40 ± 1 kHz) during thermosonic inactivation, respectively. The results showed that both thermal and thermosonic treatment could effectively reduce the PPO activity in strawberry juice. Moreover, the effect of PPO inactivation was remarkably enhanced by the FSFPU treatment, and dual-frequency mode ultrasound had the highest effect of PPO inactivation. It can be concluded that flat sweeping frequency and pulsed ultrasound can be used as an efficient and low-cost method to facilitate the inactivation of PPO in strawberry juice. [ABSTRACT FROM AUTHOR]

Interfaces formed by Al-Al thermocompression bonding were studied by the transmission electron microscopy. Si wafer pairs having patterned bonding frames were bonded using Al films deposited on Si or SiO2 as intermediate bonding media. A bond force of 36 or 60 kN at bonding temperatures ranging from 400-550°C was applied for a duration of 60 min. Differences in the bonded interfaces of 200 μm wide sealing frames were investigated. It was observed that the interface had voids for bonding with 36 kN at 400°C for Al deposited both on Si and on SiO2. However, the dicing yield was 33% for Al on Si and 98% for Al on SiO2, attesting for the higher quality of the latter bonds. Both a bond force of 60 kN applied at 400°C and a bond force of 36 kN applied at 550°C resulted in completely bonded frames with dicing yields of, respectively, 100% and 96%. A high density of long dislocations in the Al grains was observed for the 60 kN case, while the higher temperature resulted in grain boundary rotation away from the original Al-Al interface towards more stable configurations. Possible bonding mechanisms and reasons for the large difference in bonding quality of the Al films deposited on Si or SiO2 are discussed. [ABSTRACT FROM AUTHOR]

The study of the physical mechanisms driving Cu-Cu wafer bonding allowed for reducing the bonding temperatures below 200 °C. Metal thermo-compression Cu-Cu wafer bonding results obtained at such low temperatures are very encouraging and suggest that the process is possible even at room temperature if some boundary conditions are fulfilled. Sputtered (PVD) and electroplated Cu thin layers were investigated, and the analysis of both metallization techniques demonstrated the importance of decreasing Cu surface roughness. For an equal surface roughness, the bonding temperature of PVD Cu wafers could be even further reduced due to the favorable microstructure. Their smaller grain size enhances the length of the grain boundaries (observed on the surface prior bonding), acting as efficient mass transfer channels across the interface, and hence the grains are able to grow over the initial bonding interface. Due to the higher concentration of random high-angle grain boundaries, this effect is intensified. The model presented is explaining the microstructural changes based on atomic migration, taking into account that the reduction of the grain boundary area is the major driving force to reduce the Gibbs free energy, and predicts the subsequent microstructure evolution (grain growth) during thermal annealing. [ABSTRACT FROM AUTHOR]

Copper (Cu) is used as an interconnect material in many applications owing to its high thermal, electrical conductivity and excellent electromigration resistance. Though this material has many advantages, the main drawback is that it gets oxidized on exposure to air. Thermo-compression bonding is a wafer bonding technique that uses metal layers for heaping wafers, which aids in attaining outstanding electrical conductivity without weakening the mechanical properties. The adsorbed oxide layer hurdles the proper bonding to happen between the wafers. In order to enhance the diffusion between the metal layers, the copper oxide layer should be removed which necessitates the requirement of high temperature, pressure, long bonding time and the inert gas atmosphere throughout the Cu-Cu thermo compression wafer bonding process. Simultaneous application of high temperature and pressure for a long time leads to the deterioration of the underlying sensitive components. This paper aims to present several techniques such as surface treatment, chemical pretreatment, surface passivation, crystal orientation modification, stress gradient in the thin film and formic acid vapour treatment which are used in order to avoid the deterioration of underlying sensitive devices and to obtain a proper bonding between the wafers at low temperature and pressure. [ABSTRACT FROM AUTHOR]

Highlights • Sunflower bark can replace flax shives in particleboards made with a binder. • Self-adhesion is better with flax shives thanks to their biochemical composition. • Binderless boards made of flax shives present interesting bending strength. • Fire resistance of binderless particleboards is better than that of boards containing UF resin. Abstract In order to replace wood in particleboard manufacturing, two agricultural by-products were studied: the flax shives and the sunflower bark, which are abundant, renewable and little valorized raw materials. Sunflower bark in particular is very few studied. This study will demonstrate the possibility of using sunflower bark in particleboards and how to modulate the manufacturing process to take the benefits of both studied agroresources. These plant based particles present interesting porous structures for using as materials for building insulation or as furniture. To obtain totally biosourced materials, the plant based particles were self-bound by a thermocompression process with water. The properties of these materials were compared with particleboards made of the same plant based particles with a classical urea-formaldehyde binder. Particleboards of two target densities are compared: 350 and 500 kg m−3. Both agroresource materials do not present the same behavior to self-binding or classical binding. Flax shives are more adapted to self-binding process thanks to their biochemical composition and their morphological structure. These different boards were characterized according to mechanical and thermal properties, resistance to water and to fire. The type of agroresource or of binder does not influence the thermal conductivity. The denser binderless boards show better resistance to fire. The main defect of binderless boards is their too low resistance to water compared to boards made with a synthetic binder. [ABSTRACT FROM AUTHOR]

Abstract In this paper, new type Cu nanoaggregates (Cu NAs) were designed, and the Cu-Cu bonding by Cu NAs was investigated. The Cu NAs were obtained by agglomeration of the synthesized 5 nm Cu nanoparticles (Cu NPs). Compared to ultra-small Cu NPs, the collection difficulties were effectively solved and the antioxidation properties were also enhanced by the formation of Cu NAs. After sintering at 250 °C for 60 min, the Cu NAs film achieved a low electrical resistivity of 4.1 μΩ cm, which is only 2.5 times larger than that of bulk Cu. A high strength Cu-Cu bonding joint of 25.36 MPa can also be achieved via sintering of Cu NAs at 250 °C under a low bonding pressure of 1.08 MPa. After characterizations of Cu-Cu bonding interfaces and fracture structures of bonded joints, the Cu-Cu interconnection was demonstrated to be tightly contacted, sufficiently diffused and with high purity. In addition, a sintering and bonding mechanism by Cu NAs were proposed, explaining the key role played by ultra-small Cu NPs on the shell layer of Cu NAs. According to the advantages, Cu NAs are expected to be ideal substitutes to traditional solders, which have a huge application prospect in electronics packaging. Highlights • New type of Cu nanoaggregates composed of 5 nm Cu nanoparticles were designed. • Collection difficulty was solved and antioxidation performance was enhanced. • High sintering and bonding properties of Cu nanoaggregates were achieved. • Sintering and bonding mechanism of Cu nanoaggregates were proposed. [ABSTRACT FROM AUTHOR]

Au–Au‐bonding‐based wafer‐level vacuum packaging technology using in‐plane feedthrough of thick Au signal lines was developed for high‐frequency micro electromechanical system (RF MEMS). Compared with conventional technology based on glass frit bonding, the developed technology is advantageous in terms of smaller width of sealing frames, lower process temperature, and smaller amount of degas. To guarantee the hermetic sealing, the adhesion between the thick Au lines and a SiOx dielectric frame is improved by an Al2O3 interlayer by atomic layer deposition. The steps of the dielectric frame above the thick Au lines are absorbed by an electroplated Au seal ring planarized by fly cutting. The thermocompression bonding of the Au seal rings of 20‐100 μm width was done at 300 ºC. A cavity pressure of about 500 Pa or lower was measured by "zero balance method" using Si diaphragms. Vacuum sealing was maintained for more than 19 months, and the leak rate is less than 8×10‐16 Pa m3/s. The isolation of open signal lines was measured up to 10 GHz for different designs of the sealing ring and SiOx dielectric frame. The influence of the in‐plane feed through to the isolation is as low as 2‐3 dB, if the width of the sealing ring is 20 μm and the thickness of SiOx dielectric frame is larger than 10 μm. The developed wafer‐level packaging technology is ready for applications to an radio frequency (RF) MEMS switch. [ABSTRACT FROM AUTHOR]

The demand for high-performance, high-functionality packages for integrated circuits continues to grow. Three-dimensional (3D) integration is strongly being pursued to meet this demand and has started to reach maturity and industrial adoption. As advanced 3D system designs progress, requiring higher 3D interconnect density with pitches of 10 mm and lower, traditional chip attachment through solder bump technology will likely face complex manufacturing and reliability challenges. Cu-Cu thermocompression bonding has been proposed as a key 3D-enabling technology and alternative to solder. One of the main issues challenging its commercialization in high-volume manufacturing is the sensitivity of Cu-Cu bond quality to prebond surface conditions. This is especially true for die bonding applications which have limited rework options once chips have been singulated. This article outlines further development and demonstration of a tack and collective bonding scheme for Cu-Cu thermocompression bonding. This approach mitigates many of the thermal and throughput issues of a chip-level Cu-Cu attachment process by performing the quick chip alignment at a low temperature and then subsequently completing all Cu bonding simultaneously. The specific use of an intermediate handle wafer between the tack and collective bonding steps allows chips to be reconstructed into a wafer form that facilitates the cleaning and surface preparation of the chips before bonding using standard wafer processing equipment. A chip-to-wafer test structure designed for Cu pillar-to-pad bonding was used as part of this demonstration and illustrates the feasibility of the application. Full transfer of chips to a receiving device wafer using the tack and collective bonding process is shown with electrical test results and selected bond-integrity metrology confirming substantial bond yield and strength. [ABSTRACT FROM AUTHOR]

Abstract This study was designed to compare the effect of thermosonication and thermal treatment on color and anthocyanins stability of natural and copigmented barberry juice during processing and storage. Addition of copigments significantly induced the hyperchromic effect and increased the total phenolic and antioxidant activity of barberry juice. Copigmentation especially at 1:2 M ratio, markedly enhanced the color and anthocyanin stability of barberry juice during processing. Thermal treatment negatively affected the phytochemical compounds, whereas thermosonication especially at low amplitude showed no significant changes. A similar trend in the degradation of anthocyanins and color instability of samples was observed during storage. Copigmentation, especially with licorice extract, considerably increased the half-life of anthocyanins and well preserved pelargonidin 3-glucoside and the color parameters of the juice during storage. The results indicate that licorice extract can be a good alternative to synthetic copigments and the application of thermosonication maintains the effectiveness of copigmentation reaction. Industrial relevance Barberry (Berberis vulgaris) is one of the most important medicinal plants which is mainly cultivated in Iran. Barberry fruits are used in preparing sauces, jellies, candies, marmalades and especially juice drinks. Like other berry fruits, barberry contains high amounts of anthocyanins. Due to the highly instability of these pigments, the preservation of these nutrients during industrial processing and storage of barberry juice is very important. Intermolecular copigmentation of anthocyanins with phenolic compounds, especially with phenolic extract from various plant species, is an efficient method to stabilize these compounds. Moreover, because of the adverse effect of thermal treatment on the copigmentation reaction and the degradation of nutritive compounds of fruit juice, there is a need for non-thermal processing techniques like sonication or high pressure to preserve the nutritional and sensory properties of juices. Therefore, in this study, for the first time, the simultaneous use of thermosonication and copigmentation with ferulic acid and licorice extract on the stability of color and anthocyanins of barberry juice was evaluated. The results of our study revealed that licorice extract due to having various flavonoid compounds such as liquiritin and isoliquiritin can be a good alternative to synthetic copigments. Furthermore, the application of thermosonication in comparison with thermal treatment maintains the effectiveness of copigmentation reaction. Highlights • Thermosonication insignificantly affected anthocyanin and color stability. • The addition of copigments enhanced the anthocyanins and color stability. • Licorice extract showed the highest protection effect on anthocyanins. • Copigmentation and thermosonication synergistically protected anthocyanins. [ABSTRACT FROM AUTHOR]

The incorporation of a micro copper pillar is considered as the major interconnection method in three-dimensional (3D) integrated circuit (IC) intergradation under high-density I/O conditions. To achieve low-temperature bonding, this study investigated the thermosonic flip chip bonding of a copper pillar with a tin cap. The effect of bonding force on bonding strength was studied, and an average bonding strength 2500-g (approximately 84.8 MPa) was obtained in 2-s, at an optimized bonding force of 0.11 N per 40 μm pillar bump, and substrate temperature of 200-°C. Additionally, the effect of the bonding force on bonding interface microstructure and intermetallic compounds (IMCs) was also investigated. Tin whiskers were also observed at the bonding interface at low bonding forces. [ABSTRACT FROM AUTHOR]

Abstract To evaluate the evolution and significance of organic pores in marine shales, samples with high organic matter and low thermal maturity were collected from the Mesoproterozoic Xiamaling Formation in the Xiahuayuan region, Hebei province, northern China. Samples underwent a thermocompression simulation experiment. Scanning electron microscope (SEM) observations, N 2 /CO 2 gas adsorption analyses, and statistical calculations assured the qualitative and quantitative characterization of organic pores during kerogen maturation. Results demonstrated that pores largely evolve from macro- and meso-sizes to meso- and micro-sizes along with increasing pore volumes. As the total proportion of organic pores reached over 50% from the maturation (345 °C and 375 °C) to high maturation stages (440 °C), they provided the main space for gas storage. Organic pore types changed from hydrocarbon shrinkage cracks to hydrocarbon bubble pores and hydrocarbon dissolution pores. Additionally, organic porosity sharply increased initially followed by as low decrease as the samples were heated to the post maturation (500 °C) stage. Highlights • Thermocompression experiment was done to simulate the evolution of organic pores. • Qualitative and quantitative methods were used for organic pore characterization. • Organic porosity in each stage during the kerogen maturation process was evaluated. • The influence of organic pores in gas accumulation and storage was emphasized. [ABSTRACT FROM AUTHOR]

The development of composites based on vegetal fibers requires a good control of manufacturing process. The aim of this work is to determine the key parameters to produce high grade flax/epoxy unidirectional laminated composite by thermocompression. So, many processing parameters have been tested and ranked according to their influence on mechanical properties. Since variability can be high for this kind of materials, statistical analyses have been used to determine if properties variations were significant or not. Among all studied parameters, the three which have been identified as first rank influence on mechanical properties are: fibers conditioning, curing pressure and exit plate temperature. [ABSTRACT FROM AUTHOR]

Hermetic packaging plays an important role for optimizing the functionality and reliability of a wide variety of micro-electro-mechanical systems (MEMS). In this paper, we propose a low-temperature wafer-level hermetic packaging method based on the thermo-compression bonding process using an electroplated Cu sealing frame planarized by a single-point diamond mechanical fly-cutting. This technology has an inherent possibility of hermetic sealing and electrical contact as well as a capability of integration of micro-structured wafers. Hermetic sealing can be realized with the sealing frame as narrow as 30 μm at a temperature as low as 250 °C. At such a low bonding temperature, a less amount of gases is desorbed, resulting in a sealed cavity pressure lower than 100 Pa. The leak rate into the packages is estimated by a long-term sealed cavity pressure measurement for 7 months to be less than 1.67 × 10 −15  Pa m 3  s −1 . In addition, the bonding shear strength is also evaluated to be higher than 100 MPa. [ABSTRACT FROM AUTHOR]

Copper pillar micro bump is one of the platform technologies, which is essentially required for 2.5D/3D chip stacking and high-density electronic components. In this study, Cu-Cu direct thermo-compression bonding (TCB) and anisotropic conductive paste (ACP) bonding methods are proposed for Ø 100 µm Cu-pillar bumped flip-chips. The process parameters including bonding temperature, bonding pressure and time are verified by die shear test and SEM/EDX cross-sectional analysis. The optimal bonding condition for TCB with regards to bonding pressure was defined to be 0.5N/bump at 300 °C or 0.3N/bump at 360 °C. In the case of ACP bonding, the minimum bonding pressure was about 0.3N/bump for gaining a seamless bonding interface. [ABSTRACT FROM AUTHOR]

Flexible and wearable sensors with high sensitivity are being expected for highprecision detection of subtle motions in human joints. In this study, we develop a graphene-based elastomer with tunable dielectric properties, which was further employed to construct a flexible capacitive sensor with highly anisotropic responses to the out-of-plane bending and in-plane stretching. To fabricate such a sensor, functional graphene derivatives are uniformly dispersed in a thermoplastic polyurethane (TPU) matrix and then aligned by a thermo-compression process. The uniform dispersion enables to elevate dielectric performance in composites leading to a high relative permittivity value of 97.3. In addition, adjacent graphene flakes are parallel to the hot plates due to the thermo-compression- induced alignment, thus behaving as microcapacitors to contribute to the sensitivity enhancement in the resulting sensors. Particularly, such sensors exhibit a sensitive response to the out-of-plane bending (30-180°), but are insensitive to the in-plane stretching (0-40 N). We further demonstrate that this sensor has a potential application in the field of virtual typing output. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the microstructure evolution and the resulting change in mechanical properties in a Ag@Sn TLP bondline during reflow and thermal aging. A Ag@Sn high-remelting-point bondline was rapidly achieved with thermocompression bonding of Ag@Sn powder in only 5 min at 250 °C. After reducing the thickness of the Sn coating on the Ag particles, the main phases in the resulting bondlines changed from Ag/Ag3Sn to Ag/ζ-Ag, increasing the remelting temperatures to 480 °C and above. The voids were effectively controlled by reducing the thickness of the Sn coating, thereby increasing the shear strength by 38%. The large surface area of the Ag/Sn interface, provided by a high density of core–shell Ag@Sn particles, enabled the rapid formation of an interconnection that is entirely composed of Ag and ζ-Ag. After thermal aging, the main phases transformed from Ag/ζ-Ag to Ag/Ag (Sn) solid solution/ζ-Ag, which causes an increase in the remelting temperature of aged interconnections up to 724 °C. The thermal aged samples showed slight decreases in shear strength, but the morphology of the fracture surfaces indicated better ductility. [ABSTRACT FROM AUTHOR]

Reducing energy consumption for future buildings using bio-based insulation materials is currently one of the most attractive research pursuits. The specific purpose of this research was to optimize thermo-pressing conditions for new low-environmental-impact bio-insulation fiberboards from bamboo fibers and protein-based bone glues. The microstructure, thermal insulation, water sensitivity, and mechanical properties of these fiberboards were investigated in this study. As illustrated by the results, protein-based bone glue acts as a good internal binder for bamboo fiberboards when 30% (w/w) of glue was added and elaborated under specific thermo-pressing conditions (150 kgf/cm 2 , 160 °C) during 15 min. Indeed, this board presents the best mechanical properties and water resistance due to the effective adhesion of the proteins. The thermal conductivity of all the fiberboards is in a low range, between 0.0582 and 0.0812 (W.m −1 K −1 ) at 57% RH and 25 °C, and it changes according to relative humidity levels and moisture content variation. The bamboo fibers have great potential for buildings thermal insulation with a thermal conductivity below 0.082 Wm −1 K −1 . [ABSTRACT FROM AUTHOR]

The influence of wafer bonding and post-bond annealing conditions on the (cavity) void size and distribution was investigated theoretically and verified experimentally. Based on Cu-Cu thermo-compression bonding at 175 °C for 30 min and subsequent annealing at 200 °C for 1, 6 and 24 h, respectively, in both cases the total void surface reduces with the duration of the heat treatment, showing good correlation between theory and experiment. However, the experimental results revealed that the average void size increases while voids number decreases, which is a deviation from the prediction of the physical model. [ABSTRACT FROM AUTHOR]

Acrylic resin with a fast curable property has been used in low temperature ACFs applications. However, its poor thermo-mechanical property was a concern for solder ACFs applications. In this study, a novel thermomechanical analysis (TMA) method was introduced to measure its polymer rebound amounts due to pressures removal after a thermo-compression (TC) bonding process. Polymer resin was laminated between two silicon chips (7 ∗ 7 mm 2 ), and then a compressive mode TMA measurement was done on the prepared samples. Constant compressive pressures were applied until the temperature was gradually increased to target temperature, and the forces were removed at the target temperatures. The polymer rebound was measured by monitoring the z-axis dimension change after the compressive forces was removed. In addition, the effects of bonding temperatures (from 150 to 250 °C) and the bonding pressures (1, 2 and 3 MPa) on the SnBi58 (139 °C melting point) solder joints morphologies and joint resistances were evaluated to investigate acrylic resin property and find out the optimized bonding conditions for low Tg acrylic-based solder ACFs applications. [ABSTRACT FROM AUTHOR]

Cinnamaldehyde (CIN) loaded amorphous PLA films were obtained by casting, using ethyl acetate as solvent. Likewise, bilayer films were obtained by thermocompression of the PLA active layer and compression moulded cassava starch (S) films or semi crystalline PLA films. Starch-PLA laminated materials were considered to improve the barrier capacity (high oxygen barrier through the starch layer and high water vapour capacity through the polyester layer), while CIN incorporation confers antimicrobial activity on the films. The PLA bilayers were obtained for comparison purposes. The antimicrobial activity of the CIN loaded PLA films and S bilayer films was proved against Escherichia coli and Listeria Innocua through in vitro tests, which indicates that the active amount released into the growth medium exceeded the minimum inhibitory concentration (MIC) of both bacteria. The release kinetics of the active compound in different food simulants demonstrated that a part of CIN was tightly bonded to the PLA matrix, whereas the free compound diffused more easily through the starch layer, making S bilayers more active against the bacteria when the starch layer was in direct contact with the culture medium. CIN entrapped in PLA bilayers did not exhibited any antibacterial effect due to its release inhibition, associated to its bonding within the PLA matrix and the lower degree of relaxation in the semi crystalline PLA layer in contact with the food simulants. [ABSTRACT FROM AUTHOR]

Extensible quantum computing architectures require a large array of quantum bits operating with low error rates. A quantum processor based on superconducting devices can be scaled up by stacking microchips that perform wiring, shielding, and computational functionalities. In this article, we demonstrate a vacuum thermocompression bonding technology that utilizes thin indium films as a welding agent to attach pairs of lithographically patterned chips. At 10 mK, we find a specific dc bond resistance of 49.2 μΩcm2. We show good transmission up to 6.8 GHz in a tunnel-capped, bonded device as compared to a similar uncapped device. Finally, we fabricate and measure a set of tunnel-capped superconducting resonators, demonstrating that our bonding technology can be used in quantum computing applications. [ABSTRACT FROM AUTHOR]

The main goal of the study was to design the laminating head for an industrial robot that would be competitive from the aspect of the price and versatility and therefore suitable for the SMEs. A set of experiments were carried out to analyse key parameters during the laminating process of PA12-CF60 material. [ABSTRACT FROM AUTHOR]

We transferred AlGaN/GaN high-electron-mobility transistors (HEMTs) from a sapphire substrate to a copper plate using a hexagonal boron nitride (h-BN) epitaxial lift-off technique. The bonding adhesion between the HEMTs and the copper plate is improved by optimizing Au-Au thermocompression processes and removing the h-BN residual layer after the lift-off. Thermal resistance estimated by Raman thermography is as low as 6 mm∘C/W, which is comparable to that of a HEMT grown on SiC substrate.As a result, the reduction in Id versus Vds due to self-heating effect is suppressed to a negligible level. These results indicate that the substrate transfer technique is effective for achieving high-power performance of GaN-based electron devices. [ABSTRACT FROM AUTHOR]

SUMMARY This paper describes hermetic seal wafer bonding using Al covered with thin Sn as an antioxidation layer. The bonding temperature is below 400 °C, which is the maximum temperature of CMOS-LSI backend process. Gas tightness over 3000 h at room temperature and sealing stability through heat treatment under a typical reflow condition of 260 °C for 10 min were confirmed for samples bonded at 370 °C and 380 °C. A key for successful hermetic seal bonding is relatively high bonding pressure and stress concentration on sealing frames as narrow as several micrometers. The results of SEM and EDX analysis suggested that the bonding was due to direct Al-Al bonding, while Sn was diffused sparsely among Al grain boundaries. The developed bonding technology is usable for wafer-level integration of LSI and MEMS in conjunction with hermetic sealing. [ABSTRACT FROM AUTHOR]

Massively parallel chip assembly based on multi-interposer block concept is demonstrated for large-area heterogeneous system integration. The chips are aligned in parallel by liquid surface tension and assembled on the Si interposers through oxide-oxide bonding at room temperature without thermocompression. 3-D Cu sidewall interconnects (the width is approximately 20~\mu \textm ) climbing over 100- \mu \textm -thick self-assembled chips are formed with a spin-on thick photoresist by electroplating. In addition, 3-D Cu interconnects with a width of nearly 10~\mu \textm are successfully formed across polyimide slopes formed on the sidewall of self-assembled chips. The electrical properties of the 3-D sidewall interconnects are characterized by the daisy chains, resistance distribution, and characteristic fluctuation of CMOS fabricated on the self-assembled chips. [ABSTRACT FROM AUTHOR]

This paper reports novel wafer-level vacuum sealing technology for the heterogeneous device integration for advanced micro-electronics, such as LSI integrated intelligent and autonomic sensors. Vacuum sealing was successfully achieved by thermocompression bonding using electroplated Ag bonding frames after single point diamond fly-cut planarization. At a bonding temperature of 350 °C, the average bonding shear strength of around 200 MPa was obtained, and the leak rate of the sealed cavities was lower than 3.6 × 10–14 Pa m 3 /s. Shear deformation by high speed mechanical cutting during planarization is demonstrated to induce fine Ag grains on the surface of the bonding frame, which promotes atomic diffusion through grain boundaries, relating to the obtained high shear strength at a relatively low temperature. Simultaneously TiN barrier layer sufficiently inhibits Ag atomic diffusion into a Si substrate during a heating process, which is confirmed by the secondary ion mass spectrometry (SIMS). The developed process is useful for the advanced wafer-bonding-based vacuum packaging for stepped micro structures and temperature-sensitive devices in terms of high reliability, simple pre-treatment and low cost. [ABSTRACT FROM AUTHOR]

Flip chip thermo-compression bonding (TCB) involves the use of heat and pressure to simultaneously form interconnections for microelectronic packaging. In-situ measurements of thermo-mechanical stresses that arise during this bonding process could provide unique insight to help better understand the TCB process. A 4 mm × 3 mm × 500 μm complementary metal-oxide-semiconductor (CMOS) sensor chip with an 8 × 8 array of Au-bumped sensor pads was developed for this purpose. It was designed to record XYZ force and temperature signals from bump locations, during a simulated flip chip process similar to TCB. In-situ measurements during simulated TCB events proved useful for tilt detection, thermal gradient characterization, and thermal expansion measurements. Further interpretation of the signals proved tilt and other thermo-mechanical effects were induced by thermal expansion mismatches. The most thermo-mechanically stressful stage of bonding was found to occur during thermal transients, specifically during bond head ramping. Further analysis concluded the actual time necessary to heat the bumps was less than 0.5 s. Finally, the lateral thermal gradient across the sensor chip was calculated to be smallest in the central bump locations, and largest in the bump array corners due to warpage, tilt, and heat sink effects of the digital logic region. [ABSTRACT FROM AUTHOR]

Properties of aluminum thin films for thermocompression bonding have been studied in terms of surface roughness, grain size, and grain orientation by AFM, SEM, XRD and EBSD for thermocompression bonding. Al films were sputter deposited directly on Si and thermally oxidized Si wafers, respectively. The resulting Si/Al and Si/SiO 2 /Al sample types were compared after annealing (300–550 °C) in vacuum. The Si/SiO 2 /Al film samples showed higher surface roughness than the Si/Al samples. The as-deposited films had (111) preferred orientation, while (100) and (110) oriented Al grains were also present in Si/SiO 2 /Al samples. The Si/SiO 2 /Al samples and Si/Al sample annealed at 550 °C had a conical <111> texture. The observed evolution of the grain structure with annealing temperature is discussed in terms of native oxide, surface roughness, diffusivity and grain orientation dependent mechanical properties in order to shine light on previously observed differences in Al Al thermocompression wafer-level bonding with Si/SiO 2 /Al and Si/Al wafers. [ABSTRACT FROM AUTHOR]

Damascene process compatible Copper (Cu) surface passivation, ultra-smooth surface and enhanced Cu diffusion at the bonding interface are the key requirements for high quality, low temperature and low pressure Cu-Cu bonding for 3D integration applications. Manganin alloy deployed in this work as a passivation layer, performs dual role of protecting Cu surface from oxidation even at higher temperature (<300 °C) and provides surface smoothness of about 0.8 nm. Furthermore there is an inherent Cu 〈1 1 1〉 oriented plane formation with Manganin alloy passivated Cu surface. All the aforementioned factors are key enablers in enhancing diffusion of Cu across the bonding interface. This led to high quality Cu-Cu thermocompression bonding at sub 150 °C temperature and at a nominal contact force of 5 kN. Very low specific contact resistance of 1.45 × 10 −7 Ω-cm 2 and excellent bond strength of 186 MPa is clear evidence of the efficacy of optimized ultra-thin Manganin alloy as a passivation layer. [ABSTRACT FROM AUTHOR]

During operation, miniaturized thermosonic Cu ball bond interconnects on Al pads occurring in microelectronic devices experience thermomechanical cyclic stresses, which lead to a degradation and subsequent fatigue fracture at the bond interface. Standard static tests, however, ignore the performance of such bonds under cyclic loads. Therefore, a new mechanical fatigue testing method tailored for such interconnects has been introduced, allowing to study their high cycle fatigue behavior in reasonable time. By means of a vibrating system and a special specimen setup cyclic stresses are mechanically induced at the bond interface causing fatigue lift off, where the bond is separated at its weakest site. For this purpose, two distinct specimen preparation methods basing on industrially applicable soldering techniques are suggested and can be used equally, depending on the focus of the investigation and the availability of the required testing structures. The first method - “single bond testing” - allows to test each bond individually regardless of the chip layout. In contrast, the second test method - “multiple bond testing” - allows to test several bonds simultaneously. To interpret and analyze the stresses occurring at the bond interface during these tests, finite element analyses were conducted. In the present study both methods are applied to Cu Al ball bonds of the same quality and chip layout. It is shown that the aluminum is responsible for the fatigue crack initiation and propagation processes as confirmed by fractographic analyses of the fatigued bond interfaces. It can be concluded that the proposed fatigue test method is a powerful alternative screening method for such miniaturized bond interfaces, which allows to reveal their mechanical fatigue behavior in reasonable time and to identify the weakest link of the tested bond interface. [ABSTRACT FROM AUTHOR]

The requirement for closely coupled, highly integrated circuits in the semiconductor industry has spawned alternative packaging innovations such as 2.5-D/3-D integration. The incredible potential of this alternative comes with great challenges, not the least of which is the unprecedented reduction in package interconnection pitch. Market acceptance of new finepitch microelectronic products is strongly dependent on the development of flawless assembly processes that align with the traditional Moore-like expectation of higher performance without cost penalty. One such process is the application of flux to the interconnect surfaces to achieve effective joining. Insufficient flux quantity or flux activity can impede the formation of solid, reliable joints, whereas excessive quantities or activity can cause solder bridging or difficulties with downstream operations such as residue cleaning or underfill reinforcement. This delicate balance, already complex for traditional chip joining, is further challenged by the geometrical and spatial reductions imposed by pitch miniaturization, especially where large die, with over 100,000 interconnects, are concerned. This article presents an overall development protocol to evolving a flux dipping operation to production-level thermocompression assembly of large die (8 x 11 x 0.780 mm) with 11,343 ultrafine pitch (62 µm) copper pillar interconnections. After reviewing the state of the art for fluxing technology and detailing the specific technical issues, we present and defend the chosen flux application approach with its corresponding parameters of interest. Physical and chemical characterization results for selected flux material candidates are reported in conjunction with an analysis of how their properties correlate to the flux dip application parameters. As part of this fundamental understanding, we investigate and report on flux dip coating behavior and how it compares to other industrial dip coating applications. Finally, the results of process assembly experiments in a production-type environment are reviewed and discussed with respect to the previous characterizations. These experiments span downstream assembly process compatibility (i.e., cleaning and underfill) as well as product reliability. [ABSTRACT FROM AUTHOR]

Surface passivation plays a dual role of protecting copper (Cu) from getting oxidized and reducing the surface roughness of Cu thin film and thus enables low-temperature Cu–Cu bonding. In this paper, we utilized an oxidation resistive, CMOS compatible copper–nickel-based alloy, constantan as a passivation layer, as it does not get oxidized at room temperature and is also CMOS damascene process compatible. Systematically optimized ultrathin, constantan (2 nm) on Cu surface not only protected Cu from oxidation but also reduced the surface roughness to about 0.7 nm, which led to Cu–Cu bonding at a temperature as low as 150 °C at \mathsf 4 bar pressure. Cross-sectional TEM of bonded Cu layer reveals very significant interdiffusion and grain growth between the Cu films resulting in a zigzag bonding interface and the presence of Cu grains that extend across the entire bonding layer. Furthermore, reliability investigation of passivated Cu bonded structure was demonstrated using current stressing, temperature cycling test, and relative humidity test, which suggest excellent stable bonding without electrical performance degradation. This method of alloy-based passivation is confirmed to be effective and enable low temperature, low-pressure Cu–Cu wafer on wafer bonding for 3-D integration applications. [ABSTRACT FROM AUTHOR]

In this paper, wafer-level preapplied nonconductive films (NCFs) were used to interconnect the Cu pillar/Sn-Ag microbumps for 3-D through silicon via vertical interconnection. Thermocompression bonding is a common method to interconnect chips to substrates using NCFs, and thermocompression bonding time should be reduced to increase the bonding productivity. Therefore, isothermal bonding method without heating and cooling process in bonding profile was introduced to reduce the bonding time. Solder joints bonded by an isothermal bonding method were compared to those joints bonded by a conventional ramp-up bonding method that was consist of heating, bonding, and cooling process. Final joint gap was decreased using an isothermal bonding method due to higher heating rate, and solder joint morphology was also changed according to the final solder joint gap. Furthermore, solder joint should have enough contact area to substrate metal pads without solder wetting on the Cu pillar sidewall to avoid reliability problems by Sn consumption at the solder joint. Effects of isothermal bonding parameters were investigated in terms of the bonding pressure, temperature, and time to optimize the isothermal bonding parameters for good solder joint. As bonding pressure and bonding temperature increased, solder joint gap decreased because final joint gap was determined by bonding pressures and dynamic viscosity of NCFs. Isothermal bonding times can be reduced to 10 s, because the degree-of-cure of NCFs could be over 90% after 2.2 s. As a summary, solder joint bonded with NCFs using optimized isothermal bonding parameters showed excellent bump joint resistances and solder wetting on substrate metal pads. [ABSTRACT FROM PUBLISHER]

When more than one dies are stacked vertically in 3-D integrated circuits (3DICs), the overall system yield degrades significantly. While each die can be tested before stacking, failures in 3DIC interconnects could jeopardize the entire system. In this paper, a dual-mode transceiver is proposed as a built-in-self-test/repair solution to improve the yield of direct face-to-face copper thermocompression bonding (Cu–Cu bonding). The proposed transceiver could improve the Cu–Cu bonding-based interconnect reliability with the introduction of two operation modes: the ohmic mode when Cu–Cu bonding presents low resistance and the capacitive coupling mode when Cu–Cu bonding is showing any sign of failure with high resistance at the bonding interface. Such mode sensing is self-contained in the transceiver itself with the help of the proposed resistance sensor. In this paper, we discuss the modeling of Cu–Cu bonding and the proposed transceiver design with power, latency, jitter, and crosstalk simulations followed by the design guideline for the practical implementation with yield analysis. [ABSTRACT FROM PUBLISHER]

Integration technologies involving flexible substrates are receiving significant attention owing the appearance of new products regarding wearable and Internet of Things technologies. There has been a continuous demand from the industry for a reliable bonding method applicable to a low-temperature process and flexible substrates. Up to now, however, an anisotropic conductive film (ACF) has been predominantly used in applications involving flexible substrates; we therefore suggest low-temperature lead-free soldering and bonding processes as a possible alternative for flex-on-flex applications. Test vehicles were designed on polyimide flexible substrates (FPCBs) to measure the contact resistances. Solder bumping was carried out using a solder-on-pad process with Solder Bump Maker based on Sn58Bi for low-temperature applications. In addition, thermocompression bonding of FPCBs was successfully demonstrated within the temperature of 150 °C using a newly developed fluxing underfill material with fluxing and curing capabilities at low temperature. The same FPCBs were bonded using commercially available ACFs in order to compare the joint properties with those of a joint formed using solder and an underfill. Both of the interconnections formed with Sn58Bi and ACF were examined through a contact resistance measurement, an 85 °C and 85% reliability test, and an SEM cross-sectional analysis. [ABSTRACT FROM AUTHOR]

The Postgrowth processing of GaAs/AlGaAs multilayer heterostructures for terahertz quantumcascade lasers (QCLs) are studied. This procedure includes the thermocompression bonding of In-Au multilayer heterostructures with a doped n -GaAs substrate, mechanical grinding, and selective wet etching of the substrate, and dry etching of QCL ridge mesastripes through a Ti/Au metallization mask 50 and 100 μm wide. Reactive-ion-etching modes with an inductively coupled plasma source in a BCl/Ar gas mixture are selected to obtain vertical walls of the QCL ridge mesastripes with minimum Ti/Au mask sputtering. [ABSTRACT FROM AUTHOR]

Plasma- and water-assisted oxide-oxide thermocompression direct bonding for a self-assembly based multichip-to-wafer (MCtW) 3D integration approach was demonstrated. The bonding yields and bonding strengths of the self-assembled chips obtained by the MCtW direct bonding technology were evaluated. In this study, chemical mechanical polish (CMP)-treated oxide formed by plasma-enhanced chemical vapor deposition (PE-CVD) as a MCtW bonding interface was mainly employed, and in addition, wafer-to-wafer thermocompression direct bonding was also used for comparison. N2 or Ar plasmas were utilized for the surface activation. After plasma activation and the subsequent supplying of water as a self-assembly mediate, the chips with the PE-CVD oxide layer were driven by the liquid surface tension and precisely aligned on the host wafers, and subsequently, they were tightly bonded to the wafers through the MCtW oxide-oxide direct bonding technology. Finally, a mechanism of oxide-oxide direct bonding to support the previous models was discussed using an atmospheric pressure ionization mass spectrometer (APIMS). [ABSTRACT FROM AUTHOR]

Transcorneal electrical stimulation (TcES) is one of the potential therapies to prevent retinal degeneration. This study reports on an implantable medical device for TcES. The regular TcES components, such as stimulator chips, metal wires, electrodes, and printed circuit boards (PCBs), are all packaged into the device. The device has a thin-film shape and is soft enough to bend, and thus it is placed beneath the cornea without exposure to the outside. The stimulator chip, with the function of generating precise stimulation current to prevent retinal degeneration, is flip bonded onto a flexible PCB using gold studs and thermosonic bonding process. The surfaces of the gold stud bumps are in general nonuniform. Coining is an essential pretreatment of compressing the gold stud bumps against a flat solid surface to obtain much smoother and larger surfaces. This pretreatment helps to form high-strength joints between the gold stud bumps and the PCB pads. In the packaging process, an underfill is applied in the gaps between the chips and the flexible PCB to enhance the reliability of the gold joints. A compression molding step is then conducted to cover all internal components with a silicone material. The two electrodes, which are made of gold studs, can be exposed by grinding. A coining step is followed to ensure the flatness of the two electrodes. Finally, dummy samples were made to test the biocompatibility of the device. The test results show that the packaging process can produce a biocompatible and well-sealed device. [ABSTRACT FROM PUBLISHER]

In this paper, the growth kinetics of Cu–Al intermetallic compounds formed during isothermal annealing of Pd–Cu wire bonds with different palladium distribution at 175 °C are investigated by electron microscopy and compared to bare Cu wire bonds. Transmission electron microscopy (TEM) was used to provide high resolution imaging of the Cu–Al IMCs in the as-bonded state and TEM-EDX used to analyze the concentrations of Pd at the bond interface in the as-bonded state. Cu–Al IMCs were found to grow thicker with increasing annealing duration. The growth kinetics of the Cu–Al IMCs were correlated with the diffusion process during thermal annealing. The IMC thickness for Pd–Cu wire bonds with Pd at the bond interface was found to be thinner as compared to that for Pd–Cu wire bonds with no Pd at the bond interface. Thus, the presence of palladium at the bond interface has slowed down the IMC growth. Nano-voids were found in the Pd–Cu wire bonds with Pd at the bond interface, but not in the Pd–Cu wire bonds with no Pd at the bond interface. The IMC growth rate for the Pd–Cu bonds with no Pd was found to be close to that for bare Cu for the initial annealing durations. Corresponding bond pull testing showed that Pd–Cu wire bonds containing Pd have best preserved the bond strength after 168 h aging at 175 °C due to the beneficial presence of Pd. [ABSTRACT FROM AUTHOR]

Transparent polymers have great potential when applied toward flexible devices as encapsulation or substrate materials in the fields of electronics, optics, biology, and so on because of their low costs and lightweight. The use of polymeric materials in bonding technology is indispensable due to the practicality of these materials. In general, polymer bonding can be achieved through the use of interlayer-like adhesives or through direct bonds such as ultrasonic or thermocompression bonding. Polydimethylsiloxane (PDMS) joints were achieved by surface modification via oxygen-argon plasma. Plasma treatment at various plasma power levels (150, 200, 250, and 300 W) was conducted on the PDMS surface with the modified surfaces being analyzed via contact angle measurement and X-ray photoelectron spectroscopy. Plasma-activated PDMS films were bonded without adhesives at 160 °C, which did not lead to deformation. The bond strength of the plasma-activated PDMS was measured using a T-peel test prior to and after bending cycles, and the optical transmittance of the specimens was also measured. The fractured surface was investigated via optical microscopy and scanning electron microscopy following adhesion testing. The experimental results revealed that the bond strength of PDMS was proportional to the employed plasma power level. The bond strength of PDMS decreased by approximately 10.8% after 100 000 bending cycles, indicating that plasma polymerization-assisted direct bonding could function as a versatile bonding method for polymeric materials. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Under bump metallization (UBM)–Al delamination is a high-value chip-package interaction reliability problem in flip-chip Cu pillar packaging. We devised a test vehicle for quick reliability assessment. We demonstrate that preclean is a critical step to ensure reliable UBM-Al adhesion and achieve bump shear strength >12 g/mil2 for 15- \mu \textm polymer opening. Key parameters affecting bump shear strength, such as UBM critical dimension (CD), polyimide (PI) CD, SiN CD, and PI thickness, were reviewed from both simulation and experimental standpoints and good agreement was achieved between the two. Based on the observed failure mode, a 1-D model was also proposed to correctly predict the experimental trend. Optimum design rules for Cu pillar were outlined. Chip-substrate assembly was demonstrated on 80- \mu \textm bump pitch with staggered bump configuration using mass reflow. Progressive thermal cycling was performed to evaluate package performance. Failure mode was found to be solder crack, verifying the improvement in UBM-Al adhesion. [ABSTRACT FROM PUBLISHER]

This paper presents the design of high-frequency ultrasonic transducers for micro/nano device thermosonic bonding. The transducers are actuated by piezoelectric ceramics and decoupled with their connecting parts through novel flexure decoupling flanges. First, the initial geometric dimensions of the transducers were calculated using electromechanical equivalent method, then dynamic optimization design was carried out based on three-dimensional (3-D) finite element method (FEM), and the geometric dimensions of the transducer were finally determined. Flexure decoupling flanges were presented, and the decoupling principle of the flanges was explained through compliance modeling using compliance matrix method and FEM. After that the dynamic characteristics of the transducers were analyzed through finite element analysis (FEA). The vibration frequencies and modes of the piezoelectric converter, concentrators, and transducers were obtained through modal analysis, and the displacement nodes were determined. The longitudinal ultrasonic energy transmission was presented, and the decoupling effects of the flexure flanges were compared. Finally, the transducers were manufactured and experimental tests were conducted to examine the transducer characteristics using an impedance analyzer. The experimental results match well with the FEA. The results show that the longitudinal vibration frequencies of the transducers with ring, prismatic beam, and circular notched hinge-based flanges are 126.6, 125.8, and 125.52 kHz, respectively. The decoupling flange with circular notched hinges shows the best decoupling effect among the three types of flanges. [ABSTRACT FROM AUTHOR]