High Vacuum Level Research Articles

Plasma-Generated Etchback to Improve the Via-Reliability in High-Tg Substrates Used in Multilayer PWBs for Space Electronic Packaging

High-Tg (glass transition temperature, 210 °C) woven fiber-glass reinforced multifunctional-epoxy FR-4 laminates are now becoming main trend in the fabrication of multilayer printed wiring boards (PWBs) for space application due to their inherent properties of better dimensional stability, low coefficient of thermal expansion, and the capability to withstand multiple soldering operations. In PWBs, positive etchback is a key factor to improve the plated through hole (PTH) reliability due to enhanced bond pull strength. However, high-Tg multifunctional-epoxy FR-4 laminates have higher chemical resistance, and hence, it is very difficult to get required levels of positive etchback (10– $13~\mu \text{m}$ ). The absence of positive etchback results in inadequate bond pull strength, which can lead to critical defects, such as inner layer separation, and fails to meet the basic requirements of interconnection reliability tests, such as rework simulation test and thermal stress test. Ability to withstand required number of rework simulations (five times of soldering and desoldering) and multiple thermal stress tests (generally—three times solder dips and enhanced performance—six times solder dips) is essential for all PWBs used in space electronic packaging. The popular method to get the positive etchback in drilled holes of low-Tg Printed Circuit Board (PCB) substrates prior to metallization is by chemical desmearing/etchback process. Based on the success rate of chemical desmear methods on low-Tg PCB laminates, experiments were carried out on high-Tg (210 °C) FR-4 laminates. With the experimental results, it is evident that the chemical desmearing method cannot generate the required levels of positive etchback on high-Tg multifunctional-epoxy FR-4 laminate, and sometimes, it leads to negative etchback, which degrades the reliability of PTH in PWBs. In this paper, the effect of plasma treatment—a dry process to get required level of positive etchback in high-Tg multifunctional-epoxy FR-4 laminates is studied at different vacuum levels. It is observed from the experiment that effective plasma treatment to get 10–13- $\mu \text{m}$ positive etchback is possible only at 30 mtorr and higher vacuum levels at optimized plasma etch parameters. Plasma-treated PTH of high-Tg multifunctional-epoxy FR-4 laminates exhibit higher bond pull strength and readily withstand over six dip thermal stress tests and rework simulation tests without any defect in the PTH barrel. Enhanced bond pull strength of deposited copper in the PTH barrel is attributed to the mechanical interlocking of plated copper inside the microroughened dielectric surface, which results in highly reliable 3-D contacts between the plated copper and the projected inner layer copper.

진공에서 소성 가능한 프릿을 이용한 평판디스플레이 진공실장기술

One of the important issues for fabricating the microelectronic display devices such as FED, PDP, and VFD is to obtain a high vacuum level inside the panel. In addition, sustaining the initial high vacuum level permanently is also very important. In the conventional packing technology using a tabulation method, it is not possible to obtain a satisfiable vacuum level for a proper operation. In case of FED, the poor vacuum level results in the increase of operating voltage for electron emission from field emitter tips and an arcing problem, resultantly shortening a life time. Furthermore, the reduction of a sealing process time in the PDP production is very important in respect of commercial product. The most probable method for obtaining the initial high vacuum level inside the space with such a miniature and complex geometry is a vacuum in-line sealing which seals two glass plates within a high vacuum chamber. The critical solution for the vacuum sealing is to develop a frit glass to avoid the bubbling or crack problems during the sealing process at high temperature of about <TEX>$400^{\circ}C$</TEX> under the vacuum environment. In this study, the suitable frit power was developed using a mixture of vitreous and crystalline type frit powders, and a vacuum sealed CNT FED with 2 inch diagonal size was fabricated and successfully operated.

Influence factors on the formation of magnesium nanowires prepared by physical vapor deposition

Magnesium nanowires were successfully prepared by a physical vapor deposition method, and influence factors on the formation of magnesium nanowires were discussed based on the evaporation/deposition temperature, vacuum level, magnesium vapor concentration and deposition time. The results show that the formation of magnesium nanowires occurs within a specific evaporation/deposition temperature range. Magnesium nanowires become thicker and longer and finally convert into magnesium micronparticles with the increase of evaporation temperature or decrease of deposition temperature. The vacuum level also plays a decisive role in the formation of magnesium nanowires that magnesium nanowires can only be prepared in a high vacuum level. The magnesium vapor concentration and deposition time also have significant influences on the formation of magnesium nanowires. A distribution map of magnesium nanowire is set up based on our experimental results and a criterion of supersaturation of magnesium vapors is proposed in the explanation of the formation of magnesium nanowires.

Oriented growth of magnesium nanowires by physical vapor deposition in high vacuum

[11−20]-oriented magnesium nanowires were prepared at 703K for 30min in a high vacuum level of 10−4Pa by physical vapor deposition method. The evaporation temperature and vacuum level are the two key factors in the preparation of the magnesium nanowires. A growth mechanism that the magnesium nanowires prefer to grow in the closest packed direction, which has the largest binding strength, is proposed to explain the oriented growth of the magnesium nanowires.

Effects of vacuum level and pulsation rate on milk ejection and milk flow traits in Tunisian dairy camels (Camelus dromedarius).

This work aims to compare the effects of milking at two vacuum levels (38 and 48 kPa) and three pulsation rates (60, 90, and 120 cpm) on milk production and milk flow characteristics. Six multiparous Maghrebi camels in late lactation and once daily milked were used. The best combination of setting for camel's milking was high vacuum and low pulsation rate (48 kPa/60 cpm). Milk yield and average and peak milk flow rate were the highest, while milking time was the shortest using this combination of setting (3.05 ± 0.30 kg, 1.52 ± 0.21 kg/min, 2.52 ± 0.21 kg/min, and 3.32 ± 0.31 min, respectively). Lower vacuum level lengthened milking time by more than 100 % and was not sufficient to extract milk correctly (1.69 to 2.48 times less milk yield harvested), suggesting a negative interaction with the stimulatory effect of pulsation. Higher pulsation rates did not better stimulate the camels and induced more bimodality and lower milk flow rates. Animal characteristics and liner/claw design affect machine milking and further investigations must be carried out to verify their effects and to study long-term effect of high vacuum level on udder health and teat condition.

Maintenance of high vacuum level in a compact and lightweight sealed hard-tube magnetically insulated line oscillator system

Magnetically insulated line oscillator (MILO) is compact and lightweight high power microwave tube. To maintain the MILO below 10−2 Pa, we used built-in non evaporable-getter (NEG). In comparison with other pumping technology, the NEG pump operates without power is lightweight and compact. To estimate the vacuum life in static state, we carried out experimental analysis to investigate the outgassing characteristics of the main materials of the MILO in static state. Considering the expected pumping characteristics of NEG pumps in combination with the experimental data, the conclusion is that at room temperature two NEG pumps will maintain high vacuum level in the MILO more than 250 days. Moreover, the pulse desorption characteristics of MILO under high voltage pulse operation (peak voltage 440 kV, pulse width 80 ns) were also measured. At room temperature, the evaluation shows that one NEG pump can maintain the MILO tube in high vacuum level for nearly 8 pulses.

Materials Issues in Hermetic Wafer Level Packaging Using Au Thermocompression and Au-Sn Transient Liquid Phase Bonding

The three-dimensional integration of circuits is becoming increasingly important in current and future electronics, optoelectronics, and photonics often requires a high vacuum level to properly function. To achieve this level of vacuum without using pumping systems, the chips need to be packaged hermetically. This can represent more than 70% of the fabrication cost when devices are packaged individually. In this context, wafer-level packaging (WLP) has emerged a powerful paradigm to make the process of integration cost-effective. Herein, we present recent advances in gold assisted bonding techniques to achieve a hermetic and strong bonding for large scale applications. More specifically, we will discuss design and materials issues required to enable optimized gold thermocompression (Au TC) and gold-tin transient liquid phase (AuSn TLP) bonding of 6 and 8-inch wafers. Moreover, we will also present in situ and ex situ investigations of the basic mechanisms governing these bonding processes. A deep understanding of these fundamental aspects is vital to achieve a better control of WLP technologies.Au TC bonding is obtained through two different approaches: (1) Standard flat surfaces; and (2) patterned micro-scale seal rings with grooves etched in silicon. The bonding conditions are chosen to minimize the processing steps and cost, while obtaining a strong hermetically sealed cavity. The first tests are made on deep reaction-ion etched pillars bonded to blanket wafers. Both wafers are completely coated with Ti/TiN/Au (10/100/500 nm) deposited by sputtering, acting as an adhesion layer, a diffusion barrier, and the bonding interlayer, as shown in Figure 1(a). Although the bonding withstands post manipulations, under certain conditions, cracks may develop throughout the wafers, as presented in the scanning acoustic microscopy (SAM) image of Figure 1(b). Bonding using flat seal rings is also achieved and studied using SAM, scanning electron microscopy (SEM), and shear tests to evaluate the quality of the interface.AuSn TLP bonding is achieved using a near eutectic electrodeposited AuSn layer pressed between two pure sputtered gold layers. Different thicknesses are chosen to obtain a uniform Au5Sn final phase. These layers have to be thick enough for the interdiffusion step to be long enough to obtain a uniform interface, while being as thin as possible to reduce the material cost in the integration process.The optimization of these two bonding processes requires the fundamental understanding of the thermal stability of the stacks considered. Indeed, our observations show that the formation of cracks at the interface of Au TC bonded wafers is strongly related to the thermal stability of the diffusion barrier. In order to further elucidate this phenomenon, we have undertaken prior to the wafer bonding detailed and extensive in situ and ex situ studies of the behavior of the wafers and layer stacks during thermal annealing using photo-emission electron microscopy (PEEM, Figure 1(c)-(d)), low energy electron microscopy (LEEM), SEM, atomic force microscopy (AFM) and transmission electron microscopy (TEM). The effect of pinholes in the TiN diffusion barrier on the composition and morphology of the Au layer is also studied The alloy phase formation and the intermixing rate of Au and AuSn are studied through thermal annealing combined with ex situ SEM and TEM, along with in situ PEEM. The knowledge developed during these studies allowed an optimization of the layer thicknesses and the bonding recipe.

Wafer Bonding for MEMS Vacuum Packaging

Wafer bonding emerged into a powerful technology providing robust solutions for specific manufacturing challenges in Micro- Electro- Mechanical Systems (MEMS) fabrication. Various wafer bonding processes based on different physical and chemical principles can be used in MEMS manufacturing based on the desired level of performance.Among the MEMS devices which are built using one or more wafer bonding steps the devices operating under vacuum raised new challenges for bonding-based fabrication: the need for achieving vacuum levels down to 10-4 mbar, long term stable, had to be accommodated.From the broad range of wafer bonding processes only few are compatible with vacuum applications: fusion bonding, anodic bonding, glass frit bonding and metal-based bonding. The outgassing at the bonded interface or of the bonding layer material is extremely important for vacuum applications as a high level of outgassing has a significant impact on final vacuum level in manufactured device. Additionally it has to be considered that the inner surfaces of a device cavity are expected to outgas so this is another factor imposing the low outgassing amount requirement for bonding process and bonding surfaces.The vacuum levels required would further restrict the process type for specific applications. Applications requiring high vacuum levels are very sensitive to any outgassing during bonding so in some cases a small amount of getter material may be used inside the device cavity in order to compensate for the inner surfaces’ outgassing.This work reviews the principles of vacuum encapsulation using wafer bonding. Examples showing the suitability of each process for specific applications types will be presented.A significant challenge in vacuum MEMS fabrication is the lack of analytical methods needed for process characterization or reliability testing. A short overview of the most used methods and their limitations will be presented. Specific needs to be addressed will be introduced with examples.

Thermophysical properties of the dragline silk of Nephila clavipes spider

The thermal conductivity and diffusivity of the dragline silk of the Nephila (N.) clavipes spider has been characterized by one research group to be 151–416 W m−1 K−1 and 6.4–12.3 × 10−5 m2 s−1, respectively, for samples with low to high strains (zero to 19.7%). Thermal diffusivity of the dragline silk of a different spider species, Araneus diadematus, has been determined by another research group as 2 × 10−7 m2s-1for un-stretched silk. To improve measurement reliability and repeatability and resolve the orders of magnitude discrepancy between the two different measurements, this paper measured 13 un-stretched dragline silk samples of the N. clavipes spider with different lengths using the same electrothermal technique as the first group but with a much higher vacuum level and an improved heat transfer model. The measured thermal conductivity is 1.2 W m−1 K−1 and thermal diffusivity is 6 × 10−7 m2 s−1. The measured thermal diffusivity of the N. clavipes spider silk is in the same order of magnitude as that of the diadematus spider but is 1/100–1/200 of the value by the first group. The measured thermal conductivity is 1/150–1/400 of that measured in literature. The discrepancy between this research and the first group may reside in the vacuum level and the improved heat transfer analysis. The difference in thermal diffusivity measurement between the current research and the results of the second group may be because of different species.

Accuracy Analysis of Quality Factor Measurement Based on Time Domain Method for MEMS Resonators

To reduce the measurement cost and time, a time domain measurement method of quality factor for MEMS resonator is presented in this paper. The relation curve between quality factor and vacuum level is obtained. The results indicate that measurement error is larger under high vacuum level when the sampling frequency is lower. The reason causing the error is analyzed and measurement precision is improved by increasing the sampling frequency. The measurement results indicate time domain measurement is advisable and improvable for MEMS resonator measurement.

Influence of low vacuum levels on milking characteristics of sheep, goat and buffalo

Different settings of the operating parameters (pulsator rate, pulsator ratio and vacuum) are used for milking dairy species in different parts of the world. The level of the operating vacuum in machine milking is one of the principal factors which influence the integrity of the tissues and the milk quality. High vacuum levels (&amp;gt;42 kPa) are often used to facilitate the opening of the teat canal by overcoming the biological closing forces whithin the teat sphincter, but can result in severe machine-induced teat tissue damage. In this study characteristics and performances of mechanical milking at low vacuum levels have been investigated in different dairy species. Milking times and milk productions have been obtained from milk emission curves, recorded by electronic milk-meters (LactoCorder®) during the milking at different vacuum levels of sheep, goats and buffaloes. The results of the comparative experiments clearly indicate that a low vacuum level modifies the kinetics of milk emission, the machine-on time and, thus, the throughput of milking system, in all the dairy species considered. Milk yield was satisfactory at any level tested, showing that low vacuums can be adequate to completely empty the udder. Slight differences were found across species concerning the increase in the milking time per head associated with low levels of milking vacuum Our study represents a contribution to encourage the decrease of the working vacuum during mechanical milking, also for those dairy species generally considered hard to be milked, as buffaloes. Milking should be performed applying the lowest vacuum level, compatible with not excessively prolonging milking time, in line with the animal welfare on dairy husbandry.

Influence of low vacuum levels on milking characteristics of sheep, goat and buffalo

Different settings of the operating parameters (pulsator rate, pulsator ratio and vacuum) are used for milking dairy species in different parts of the world. The level of the operating vacuum in machine milking is one of the principal factors which influence the integrity of the tissues and the milk quality. High vacuum levels (&gt;42 kPa) are often used to facilitate the opening of the teat canal by overcoming the biological closing forces whithin the teat sphincter, but can result in severe machine-induced teat tissue damage. In this study characteristics and performances of mechanical milking at low vacuum levels have been investigated in different dairy species. Milking times and milk productions have been obtained from milk emission curves, recorded by electronic milk-meters (LactoCorder®) during the milking at different vacuum levels of sheep, goats and buffaloes. The results of the comparative experiments clearly indicate that a low vacuum level modifies the kinetics of milk emission, the machine-on time and, thus, the throughput of milking system, in all the dairy species considered. Milk yield was satisfactory at any level tested, showing that low vacuums can be adequate to completely empty the udder. Slight differences were found across species concerning the increase in the milking time per head associated with low levels of milking vacuum Our study represents a contribution to encourage the decrease of the working vacuum during mechanical milking, also for those dairy species generally considered hard to be milked, as buffaloes. Milking should be performed applying the lowest vacuum level, compatible with not excessively prolonging milking time, in line with the animal welfare on dairy husbandry.

A novel mass spectrometry system for helium-4 measurement

Here we report a novel mass spectrometry measurement system (MSHE4) developed at State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences for quantifying helium-4 contents of geological mineral samples. The MSHE4 system consists of seven units, a high vacuum level generating unit, a gas purified unit, a laser heating unit, a pneumatic valve unit, an automatic control unit, a gas standard unit and a quadropole mass spectrometer unit. The unique software package, developed using LabVIEW for embedded system, allows users to control the full measurement sequences. Results from a test of the Durango apatite sample are used to illustrate the performance of the new MSHE4. We show that the constructed MSHE4 system is able to accurately measure helium-4 contents of apatite mineral, which in turn can be used to quantify the low temperature thermochronology of geological minerals in combination with measurements of uranium and thorium by LA-ICP-MS. The configuration of the MSHE4 system has following advantages: smaller volume of pipeline for gas purification, easier operation of graphic user interface for measurements, and more compact design of sample holder for single grain measurements. The separate step-heating unit can be mounted to the system smoothly. The MSHE4 system can be used for measurement of noble gases from minerals, and in turn thermochronology applications for geochemists.

Towards the use of mushroom-capped dry adhesives in outer space: Effects of low pressure and temperature on adhesion strength

Instrumented indentation apparatus and techniques were applied to the testing of synthetic gecko adhesives in an attempt to characterise their ability to function in a space environment. The indentation apparatus was capable of operating at reduced pressures, allowing a higher vacuum level (1×10−5 mbar) than dry adhesives have previously been tested under. Using a 1.5 mm spherical quartz indenter on polydimethylsiloxane (PDMS), mushroom-capped, structured dry adhesives, the effective Youngʼs Modulus of the material was found to change negligibly as a result of pressure, while no changes in adhesion were observed. The effect of time spent in vacuum was also examined. Significant changes in effective Youngʼs Modulus were observed, but no changes were noted in adhesion. Tests also showed that no significant changes to adhesion could be detected from −50 to 75 °C. These results are important for space applications because it shows that the adhesion of a mushroom-capped, synthetic, PDMS, dry adhesive is constant in various thermal and pressure environments.

Controlling the sharpness of ZnO tetrapods by restricted zinc oxidation in the open air: a low turn-on field emitter stabilized by graphene

A simple, novel and economical approach was developed for the synthesis of ZnO tetrapods through the controlled open air oxidation of a commercial zinc foil. Unrestricted by stringent criteria such as the maintenance of a high vacuum level or the usage of catalysts, this protocol yields scalable amounts of high quality tetrapods, thus highlighting its convenience over other reported methods. A thin coating of gold on top of the zinc foil is found to restrict the free open air oxidation and thus plays a pivotal role in this alternative kind of tetrapod formation. Investigations using cathodoluminescence spectroscopy confirmed the high optical quality of the tetrapods. Additionally, these tetrapods are found to exhibit an excellent electron emission performance. Finally, with the expectation of gaining better field enhancement, thermally reduced graphene oxide is attached to the tetrapods. This hybrid system is observed to possess outstanding electron emission activity with very low turn-on and threshold field values, as well as much improved stability, which were not achieved for the separate components. This indicates the potential usability of these materials in field emission nanodevices.

Combination of Moderate Vacuum Frying with High Vacuum Drainage—Relationship Between Process Conditions and Oil Uptake

This paper explores the possibility of combining moderate vacuum frying followed by post-frying high vacuum application during the oil drainage stage, with the aim to reduce oil content in potato chips. Potato slices were initially vacuum fried under two operating conditions (140 °C, 20 kPa and 162 °C, 50.67 kPa) until the moisture content reached 10 and 15 % (wet basis), prior to holding the samples in the head space under high vacuum level (1.33 kPa). This two-stage process was found to lower significantly the amount of oil taken up by potato chips by an amount as high as 48 %, compared to drainage at the same pressure as the frying pressure. Reducing the pressure value to 1.33 kPa reduced the water saturation temperature (11 °C), causing the product to continuously lose moisture during the course of drainage. Continuous release of water vapour prevented the occluded surface oil from penetrating into the product structure and released it from the surface of the product. When frying and drainage occurred at the same pressure, the temperature of the product fell below the water saturation temperature soon after it was lifted out of the oil, which resulted in the oil getting sucked into the product. Thus, lowering the pressure after frying to a value well below the frying pressure is a promising method to lower oil uptake by the product.

Texture improvement of fresh and frozen mangoes with pectin methylesterase and calcium infusion

A major problem of mango products is texture loss. The effect of commercial pectin methylesterase (PME) and calcium infusion on improvement of the texture of both fresh and frozen-thawed mango cubes was investigated in the present study. The weight gain and moisture content of mango samples were greater at relatively high vacuum level (10 kPa). The PME activity of samples infused with PME and calcium at 10 kPa increased fourfold in comparison with that of control and water-infused samples. The combined effect of PME and calcium was found to improve the texture and microstructure of both fresh and frozen-thawed mangoes. Fresh mangoes infused with PME and calcium at 10 kPa showed significantly higher firmness than control fresh samples. Frozen-thawed mangoes infused with PME and calcium at 50 kPa and atmospheric pressure had superior texture and microstructure in comparison with control frozen-thawed samples. The results of the present analysis allow for a better appreciation of the role of PME, calcium and appropriate infusion conditions in improving the texture of both fresh and frozen-thawed mangoes.

Vacuum insulation properties of phenolic foam

Characteristic properties of phenolic foam as the interstitial material of a vacuum insulation panel are investigated experimentally. For the measurement of effective thermal conductivity, a vacuum guarded hot plate (VGHP) apparatus is used and the conductivity is measured at various vacuum levels. Radiative properties are found using a Fourier transform infrared spectroscopy (FT-IR) device. Solid conductivity is estimated using the porosity of the foam. Effective thermal conductivity at high level of vacuum is measured to be 5mW/mK which is sum of solid conductivity (2.56mW/mK) and radiative conductivity (2.44mW/mK) with 5% of measurement uncertainty. The pore size of the foam is estimated to be 260μm using rarefied gas conduction theory. This ensures insulation performance of phenolic foam up to about 10−3atm. Other practical characteristics of phenolic foam as the VIP core material are also discussed.

진공급탕식 다이캐스팅법을 이용한 자동차 콤프레서용 하우징 부품 개발

Abstract A vacuum ladling die casting system is suggested as a means to obtain a high vacuum level. A high vacuum of 17.8 mmHg is obtained by sealing the inner space of the mould. The sample product is a rear-head housing for an auto-compressor, and the die-casting with 6-cavities was conducted. The flow analysis shows that the filling speed during vacuum ladling is faster than for a non-vacuum system. The air holes in the sample product were too small to be seen with the naked eye in X-ray films. Density tests show that the high vacuum ladling system reduces the internal porosity as much as 57.8% when compared to the non-vacuum system. A defective rate of only 0.17% was found from leak testing. The results of this research prove that the high vacuum die-casting process is useful for manufacturing of aluminium components under high internal pressure. Key Words : Vacuum Ladling, Compressor Housing, High Vacuum, Die Casting, Aluminium 1. 서 론 는 본 연구에서의 개발 대상부품은 자동차용 에어컨 컴프레서의 알루미늄재 하우징으로, 이 부품은 콤프레서(compressor)의 압축작용을 유지하기 위해 높은 기밀성과 내압성을 필요로 한다. 실제 부품에 작용하는 압력은 35kgf/cm

Operation of a Sealed-Tube-Vircator High-Power-Microwave Source

The high-power-microwave (HPM) sources currently under development typically require constant pumping to maintain the high vacuum levels required for operation. This pumping is often done with either a cryo- or turbopumping system, either of which would be difficult to deploy in a compact portable system. A compact sealed-tube virtual cathode oscillator (vircator) source has been developed at Texas Tech University (TTU) that does not require a bulky external vacuum pump for operation. This device has a base vacuum pressure in the low range compared to the majority of laboratory HPM sources having vacuum levels in the - range. The reduced amount of trapped gasses in the sealed-tube ultrahigh-vacuum environment has the potential to greatly impact device performance. The TTU sealed-tube vircator is useful as a testbed for studying HPM source optimization under UHV conditions. Measured operational characteristics of the tube utilizing a carbon fiber cathode and a nickel anode are presented, along with radiated microwave measurements.