Hermetic Packaging Research Articles

High Power, Thermally Efficient, X-band 3D T/R Module With Calibration Capability for Space Radar

Earth observation from space radar is based on the active electronically steerable antenna (AESA) whose performances count on reliable and powerful transmit/receive modules (TRM). To this aim, as a follow-up of the successful demonstration of a low-footprint transmit/receive hybrid module concept based on 3-D packaging and interconnect technologies (3DTRM), the interest for carrying out additional development work took a further step aiming at achieving a three-fold module performance improvement as well as at consolidating the novel proposed 3-D technology for space applications. First, the possibility of performing an AESA highly accurate calibration was implemented by embedding a wide band, high directivity directional coupler in the module circuitry without any total module footprint increase. Second, the heat extraction capability of the metal-ceramic hermetic package was enhanced through a re-design of the monolithic microwave integrated circuit (MMIC)-to-sink interface. And finally, the gallium arsenide (GaAs) MMIC high power amplifier (HPA) of the first 3DTRM version was replaced by a gallium nitride (GaN) HPA MMIC, obtaining both a higher transmit output power at 5 dB of compressed gain and an improved power added efficiency (PAE) at module level.

Surface activated room-temperature bonding in Ar gas ambient for MEMS encapsulation

Surface activated room-temperature bonding of Si and sapphire wafers in high-purity inert gas ambient was examined. Although surface activated bonding has been mainly performed in high vacuum, Si and sapphire wafers were successfully bonded in Ar gas ambient up to 90 kPa, which is almost atmospheric pressure. The dicing test proved that the bonding prepared in Ar gas ambient was strong enough for MEMS packaging, although the bonding strength was slightly decreased compared with that prepared in vacuum. Transmission electron microscope observation revealed that the bonding interface prepared in Ar gas ambient is almost the same as that prepared in vacuum. It means that Ar atoms in the bonding ambient do not hamper the interatomic bond formation at the bonding interface. Room-temperature bonding in gas ambient enables hermetic packaging of MEMS devices, such as inertia sensors, MEMS switches, and Cs vapor cells for MEMS atomic clocks at various pressures.

Water wave energy harvesting and self-powered liquid-surface fluctuation sensing based on bionic-jellyfish triboelectric nanogenerator

Due to the natural working mechanism of triboelectric nanogenerators (TENGs), potential energy stored by elastic materials may not be effectively converted into electric power, post mechanical triggering. Here, we report a practical bionic-jellyfish triboelectric nanogenerator (bjTENG) with polymeric thin film as the triboelectric material, which is shape-adaptive, with a hermetic package and a unique elastic resilience structure, similar to the behavior of a jellyfish. The charge separation in the elastic resilience of this bionic-structure is based on the liquid pressure-induced contact-separation of the triboelectric layers. On the basis of the conjunction of the triboelectrification and the electrostatic induction, a sustainable and enhanced output performance of 143 V, 11.8 mA/m2 and 22.1 μC/m2 under a low frequency of 0.75 Hz and at a water depth of 60 cm is produced, which can be used to supply power for dozens of green LEDs or a temperature sensor directly. More significantly, bjTENG is believed to be a priority technology which is attributable to its highly sensitivity, portability, and suitability for continuous detection of water level and fluctuation. Furthermore, a wireless self-powered fluctuation sensor early-warning system, which provides exact and wireless monitoring of fluctuation of a liquid surface, is also successfully developed.

Exploring growth conditions and Eu2+ concentration effects for KSr2I5:Eu scintillator crystals II: Ø 25 mm crystals

Europium doped potassium strontium iodide is a very promising scintillator for national security applications due to its ease of growth and excellent scintillation properties. For this work the fast crystal growth and scintillation properties of 1-inch diameter single crystals of KSr2I5:Eu2+ (KSI:Eu) were investigated. We focused our efforts on optimizing the growth parameters required to produce one-inch diameter crystals without decreasing the previously reported fast pulling rate of 5 mm/h. Cracking was minimized by replacing the quartz ampoules with carbon coated quartz ampoules; thus, several crack free single crystals of KSI with varying Eu2+ concentrations were grown, including a Ø 1″ by 6″ long boule with 2.5% Eu.The maximum achievable performance of each crystal was measured using small 0.012 cm3 specimens. The volumetric dependencies of the light yield, energy resolution and decay time were evaluated using KSI:Eu 2% specimens with volumes ranging from 0.012 cm3 to 18 cm3. For large volumes (≥ 9 cm3), the performance was comparable to other high performing scintillators, with light yields up to 78,200 ph/MeV and energy resolutions as good as 3.2% at 662 keV. The initial version of a hermetic package has been developed, and the stability of the sealed crystal is promising.

Self‐assembled triangular waveguide slot array for system‐on‐chip applications

New microelectronic fabrication techniques enable the creation of high-performance on-chip antennas by using new or modified antenna designs. A system's performance is normally improved by a high antenna gain which requires an electrically large aperture typically supporting an array. Consequently, array design is of particular interest for high-performance on-chip systems. The feed for an array is a challenge because it must be low loss while extending over the large aperture. A solution is the waveguide slot array which integrates antenna elements with a low-loss feeding structure. This study presents a new slot array structure which is motivated by advanced microelectronic fabrication. It comprises a triangular waveguide as the array feed, and slots for the elements. This allows fabrication by a self-assembly technique which lithographically controls the shape of a three-dimensional structure. This process is complementary metal–oxide–semiconductor compatible, enabling radio and radar system-on-chip solutions. For production, the low mass of the structure makes it inherently robust, although hermetic packaging with a radio window akin to UV-erasable eproms would be required (not included here). The design concept is demonstrated with a physical prototype operating at a low frequency. The fabrication concept is demonstrated by a physical on-chip prototype, and its performance is assessed by simulation.

Dark Current Leakage in Optoelectronic Hermetic Packages

Abstract In this work, the root cause of the increase in dark current occurring over time at high temperature in hermetic packages, such as those used in optoelectronic devices, was investigated. It was observed that hermetic Receiver Optical Subassembly (ROSA) devices show continuously increasing dark current when stressed and monitored at 85°C over an extended period of time, reaching, in some cases, values greater than 500nA. However, this increase in leakage current was recoverable once the package seal is broken, and this behavior was found to be very repeatable. Photodetectors from two different suppliers were tested and found to have dark current which is dependent on the fabrication process, as the photodetector (PD) from supplier 1 (PD1) showed three times higher leakage than the photodetector from supplier 2 (PD2). The main difference between the two photodetectors is that the polyimide layer in PD1 in significantly greater than in PD2. It was also observed that 48 hour pre-seal baking at 120°C keeps the dark current constant at much lower levels, but does not stop it completely from rising over time.

Direct sapphire to ceramic bonding for CMOS image sensor packaging using room temperature bonding technology

Abstract The aim of the study was to evaluate the use of a novel bonding technology to create a sapphire-ceramic package for CMOS image sensor devices. The package must be robust enough to be used in space flight applications: it must protect the device from external environmental conditions during testing, storage and use. A series of tests were executed to ensure the package quality. The package needs to be radiation-tolerant to ensure reliability of data in high radiation environments, such as in space. Package hermeticity is an important reliability requirement not only in space but also in other applications such as medical implants, military, nuclear inspection and telecoms. It was proved that novel bonding technique enables direct sapphire to ceramic bonding: robust packages were manufactured. A significant improvement in moisture levels was observed compared to (typically)epoxy sealed packages: detected moisture levels were of only one tenth of what is commonly seen in the stressed image sensor packages. Environmental changes had no influence on the package & device functionality or quality.

Novel integration and packaging concepts of highly miniaturized inductively powered neural implants.

This work proposes solutions to the current bulky packaged neural implants. We describe the next generation of miniaturized wirelessly powered neural interface that are distributed and free floating in the nervous system. This paper focuses on the microassembly, hermetic packaging and its effect on the inductive power link.

Liquid Cooling in an LTCC-Module for a Switched Mode Amplifier

Abstract Low Temperature Co-fired Ceramic (LTCC) is a proven packaging technology for microwave and millimetre-wave applications. Advanced low-loss material systems and improved manufacturing technology facilitate economic and highly reliable packaging solutions for automotive, telecom, medical and security applications. The fact that the substrate is hermetic facilitates unique packaging concepts where the LTCC multilayer is part of a hermetic package. However, there is a trade-off for the increasing complexity of these modules: When active devices are involved, the density of power dissipation is also rising. Liquid cooling provides an alternative where (forced air) convection cooling is not possible for lack of space or because of other limitations. With the integration of micro-channels into the LTCC-multilayer-stack the microwave-substrate becomes part of the piping for liquid cooling and brings the coolant in close contact to the heat source. As an example for such a solution a switched mode amplifier shall be presented that uses liquid cooling for the power transistor. Two different approaches for the routing of the cooling channels inside the LTCC are compared with cooling on a metal block at constant temperature. For the exact determination of all parameters, dissipated power and temperature on the die (junction temperature) a thermal test die is used instead of the transistor for the test vehicles.

Investigation of Au/Si Eutectic Wafer Bonding for MEMS Accelerometers

Au/Si eutectic bonding is considered to BE a promising technology for creating 3D structures and hermetic packaging in micro-electro-mechanical system (MEMS) devices. However, it suffers from the problems of a non-uniform bonding interface and complex processes for the interconnection of metal wires. This paper presents a novel Au/Si eutectic wafer bonding structure and an implementation method for MEMS accelerometer packaging. The related processing parameters influencing the Au/Si eutectic bonding quality were widely investigated. It was found that a high temperature of 400 °C with a low heating/cooling rate of 5 °C/min is crucial for successful Au/Si eutectic bonding. High contact force is beneficial for bonding uniformity, but the bonding strength and bonding yield decrease when the contact force increases from 3000 to 5000 N due to the metal squeezing out of the interface. The application of TiW as an adhesion layer on a glass substrate, compared with a commonly used Cr or Ti layer, significantly improves the bonding quality. The bonding strength is higher than 50 MPa, and the bonding yield is above 90% for the presented Au/Si eutectic bonding. Furthermore, the wafer-level vacuum packaging of the MEMS accelerometer was achieved based on Au/Si eutectic bonding and anodic bonding with one process. Testing results show a nonlinearity of 0.91% and a sensitivity of 1.06 V/g for the MEMS accelerometer. This Au/Si eutectic bonding process can be applied to the development of reliable, low-temperature, low-cost fabrication and hermetic packaging for MEMS devices.

Wafer-Level Hermetic Package by Low-Temperature Cu/Sn TLP Bonding with Optimized Sn Thickness

In this paper, a wafer-level package with hermetic sealing by low-temperature Cu/Sn transient liquid phase (TLP) bonding for a micro-electromechanical system was introduced. A Cu bump with a Sn cap and sealing ring were fabricated simultaneously by electroplating. The model of Cu/Sn TLP bonding was established and the thicknesses of Cu and Sn were optimized after a series of bonding experiments. Cu/Sn wafer-level bonding was undertaken at 260°C for 30 min under a vacuum condition. An average shear strength of 50.36 MPa and a fine leak rate of 1.9 × 10−8 atm cc/s were achieved. Scanning electron microscope photos of the Cu/Sn/Cu interlayers were presented, and energy dispersive x-ray analysis was conducted simultaneously. The results showed that the Sn was completely consumed to form the stable intermetallic compound Cu3Sn. An aging test of 200 h at 200°C was conducted to test the performance of the hermetic sealing, while the results of shear strength, fine leak rate and bonding interface were also set out.

Constraints and optimization of the laser microwelding process of thin metal foils

Laser microwelding of thin metal foils of various materials is established in several fields of application. Within all these application fields, a sufficient and reliable welding process is required to join thin metal foils successfully. One crucial function of the weld is often a gas-tight sealing. For instance, titanium foils provide hermetic and sterile packaging of medical implants, and vacuum insulation panels and pressure sensors are assembled from stainless steel foils. Even if gas-tightness is not the aim, weld defects lower the functionality of the product. In the case of a roll imprint process in order to structure optical surfaces on films and panels, where nano-structured nickel foils serve as masters, weld imperfections lead to failures in the optical structure. Furthermore, insufficiently welded cathode foils, which are made of aluminum, cause an increasing electric resistivity. Weld defects during laser microwelding are provoked by thermally induced distortion due to small foil thickness. The distortion causes gaps between the joining partners and can lead to a partial process abortion. Hence, metal foils have to be joined in the deep welding mode, which causes less heat conduction losses than conduction welding. In addition to a defect-free weld seam, a broad process window is required for a reliable and robust process. The process window in laser microwelding is determined by the transitions from a full penetration weld to a fusion cut regime and to an incomplete penetration weld. Furthermore, the onset of humping at higher feed rates decreases the cross-sectional area of the join and, as a consequence, the tensile strength, and has to be avoided in order to achieve a high weld quality. For the purpose of considering all mentioned constraints (deep welding regime, process window broadness, and onset of humping) while designing the process with due regard to the applied material, focal diameter, laser power, and feed rate, a deeper understanding of the process is necessary. The present work gives a qualitative and quantitative overview of the occurrence of these constraints in laser microwelding and determines the ideal working range with respect to the combination of process parameters.

Gan Transistor in Space Equipments: From Selection to Applications

Two years ago, at ESPC-2014 results of ESA activity on GaN transistor survey has been presented. The main outcome was the existence of an unknown phenomena in silicon MOSFET: the dynamic Rdson.Today we are the time of studying introduction of this technology into products. At least two suppliers (EPC- co & GaN Systems) are proposing stabilized GaN transistors components which are worth spending some time to try to implement in next generation product prototypes.Space applications aren’t very different from terrestrial ones when we speak about benefits of using GaN technology into dc-dc converters: lower losses & more compact designs thanks to higher switching frequencies. Next to reliability analyses proposed by the component vendors to be able to address the automotive markets, there is of course quite a list “space” specific questions that need also to be answered to raise the confidence that GaN will one day be put is orbit: hermetic packaging & assembly on PCBs, radiation harness, reliability impact of radiations, cooling in the absence of air flow, thermal cycling, drivers, deratings to apply…In this article we presents some prototyping results & shares some feedback & concerns about the introduction of GaN into space qualified dc-dc products.

Advanced hermetic electronic packaging based on lightweight silicon/aluminum composite produced by powder metallurgy technique

Silicon/aluminum (Si/Al) composite is a kind of lightweight electronic packaging material that received a lot of attention in the past 20 years. In this paper, a series of Si/Al composites with lowered coefficient of thermal expansion (CTE) and high thermal conductivity were produced by powder metallurgy (PM). The Si/Al composites are fully dense and have fine Si particles uniquely distributed within pure Al matrix. Three 50%Si/Al composites were designed to have strength in the range of 185–290 MPa to meet different demands, while the other properties keep invariable. Fracture toughness of the composites is measured to be 9–10 MPa·m1/2. The composites were machined to 50%Si/Al housings and 27%Si/Al lids. Both the hermeticities of housings before and after laser-beam-welding sealing are determined. The measured leak rate of composites and sealed housings is in magnitude order of 1 × 10−10 and 1 × 10−9 Pa·m3·s−1, respectively, suggesting high hermeticity. The good hermeticity is attributed to the full dense materials, good weldability, and extremely low weld porosity. The present Si/Al composites are expected to be extensively used in highly hermetic electronic packages.

Capacitively coupled pickup in MCP-based photodetectors using a conductive metallic anode

We have designed and tested a robust 20×20cm2 thin metal film internal anode capacitively coupled to an external array of signal pads or micro-strips for use in fast microchannel plate photodetectors. The internal anode, in this case a 10nm-thick NiCr film deposited on a 96% pure Al2O3 3mm-thick ceramic plate and connected to HV ground, provides the return path for the electron cascade charge. The multi-channel pickup array consists of a printed-circuit card or glass plate with metal signal pickups on one side and the signal ground plane on the other. The pickup can be put in close proximity to the bottom outer surface of the sealed photodetector, with no electrical connections through the photodetector hermetic vacuum package other than a single ground connection to the internal anode. Two pickup patterns were tested using a small commercial MCP-PMT as the signal source: 1) parallel 50Ω 25-cm-long micro-strips with an analog bandwidth of 1.5GHz, and 2) a 20×20cm2 array of 2-dimensional square ‘pads’ with sides of 1.27cm or 2.54cm. The rise-time of the fast input pulse is maintained for both pickup patterns. For the pad pattern, we observe 80% of the directly coupled amplitude. For the strip pattern we measure 34% of the directly coupled amplitude on the central strip of a broadened signal. The physical decoupling of the photodetector from the pickup pattern allows easy customization for different applications while maintaining high analog bandwidth.

Wafer-level hermetic thermo-compression bonding using electroplated gold sealing frame planarized by fly-cutting

In this paper, a novel wafer-level hermetic packaging technology for heterogeneous device integration is presented. Hermetic sealing is achieved by low-temperature thermo-compression bonding using electroplated Au micro-sealing frame planarized by single-point diamond fly-cutting. The proposed technology has significant advantages compared to other established processes in terms of integration of micro-structured wafer, vacuum encapsulation and electrical interconnection, which can be achieved at the same time. Furthermore, the technology is also achievable for a bonding frame width as narrow as 30 μm, giving it an advantage from a geometry perspective, and bonding temperatures as low as 300 °C, making it advantageous for temperature-sensitive devices. Outgassing in vacuum sealed cavities is studied and a cavity pressure below 500 Pa is achieved by introducing annealing steps prior to bonding. The pressure of the sealed cavity is measured by zero-balance method utilizing diaphragm-structured bonding test devices. The leak rate into the packages is determined by long-term sealed cavity pressure measurement for 1500 h to be less than Pa m3s−1. In addition, the bonding shear strength is also evaluated to be higher than 100 MPa.

THE ROLE OF POSTHARVEST MACHINERIES AND PACKAGING IN MINIMIZING AFLATOXIN CONTAMINATION IN PEANUT

As a tropical country with relatively high humidity and temperature, Indonesia is struggling with aflatoxin which frequently contaminates peanut. Aflatoxin is a carcinogenic toxic substance that could cause liver cancer. Due to the increasing concern on food safety, the Indonesian Drugs and Foods Agency specifies the maximum aflatoxin allowed in peanut as much as 20 ppb. However, researches showed that aflatoxin contamination in peanut in Indonesia is much higher than the threshold. The study was carried out to observe the effect of using postharvest machineries and packaging treatments on aflatoxin contamination in peanut. Reduction of postharvest processes was conducted by using series of machineries, e.g. thresher, dryer, and sheller. Packaging treatments, e.g. vacuum plastic pack, hermetic glass chamber, and polyethylene (PE) plastic wrap were carried out during storage at ambient temperature (25-27°C). The results showed that using machineries in postharvest handling produced peanut free from aflatoxin contamination. However, without effective packaging, the aflatoxin level would increase during storage. Hermetic packaging could protect peanut from the mold as indicated by low level of aflatoxin contamination.

THE ROLE OF POSTHARVEST MACHINERIES AND PACKAGING IN MINIMIZING AFLATOXIN CONTAMINATION IN PEANUT

As a tropical country with relatively high humidity and temperature, Indonesia is struggling with aflatoxin which frequently contaminates peanut. Aflatoxin is a carcinogenic toxic substance that could cause liver cancer. Due to the increasing concern on food safety, the Indonesian Drugs and Foods Agency specifies the maximum aflatoxin allowed in peanut as much as 20 ppb. However, researches showed that aflatoxin contamination in peanut in Indonesia is much higher than the threshold. The study was carried out to observe the effect of using postharvest machineries and packaging treatments on aflatoxin contamination in peanut. Reduction of postharvest processes was conducted by using series of machineries, e.g. thresher, dryer, and sheller. Packaging treatments, e.g. vacuum plastic pack, hermetic glass chamber, and polyethylene (PE) plastic wrap were carried out during storage at ambient temperature (25-27°C). The results showed that using machineries in postharvest handling produced peanut free from aflatoxin contamination. However, without effective packaging, the aflatoxin level would increase during storage. Hermetic packaging could protect peanut from the mold as indicated by low level of aflatoxin contamination.

The True Cost of Hermeticity in Microelectronic Packaging

Abstract Reliability in microelectronic packaging has been, and will continue to be, a major concern that must be taken into account early in the design of a package. Decisions made relative to packaging materials and the methods for achieving environmental protection drive many other aspects of the design, such as component selection and next higher assembly interfaces. A better understanding of current methods for achieving reliability allows the design community to determine the most appropriate packaging solution for use in a given application. Environmental protection in microelectronic packaging may be achieved both with and without hermeticity. Hermetic solutions require a means of sealing the package via laser or seam weld type processes in order to provide environmental protection to the components within the package. These packages are typically in the form of either a metal box assembly or a ceramic substrate with a soldered lead frame. Non-hermetic packaging solutions can be accomplished on a wide variety of material sets but require environmentally protective coatings to prevent damage to the packaged components. Hermetic and non-hermetic packaging solutions, in addition to various types of each, have unique advantages and disadvantages depending upon the application. Characteristics such as electrical performance, producibility, structural integrity and cost must be considered when choosing a packaging solution for an application. This paper will review current microelectronic packaging technology trends and present a trade study on the materials and methods used to achieve environmental protection.

Package Architecture and Component Design for an Implantable Peripheral Nerve Stimulation and Recording System for Advanced Prosthetics

Abstract One of the limitation of current prosthetics is the ability to provide sensory feedback to the human user. Due to this constraint, approximately 60–80 percent of amputees experience a phenomenon known as phantom limb pain, an ongoing painful sensations that to the individual, seems to be coming from the part of the limb that is no longer there. The lack of sensory feedback also limits the intuitive control of the user's hand movement, i.e. sense of grip or position. To address these limitations, we created am implantable system that could provide peripheral nerve stimulation, recording and motor control. The architecture of our Sensory-Stimulation Lead (SSL) system consist of multiple satellites connected to Draper's custom designed nerve electrodes. In this phase of the design, the implanted system is connected to a controller via percutaneous connections. The active electronics of the satellite is enclosed in a hermetic package approximately 14mm in diameter and less than 5mm thick. A custom ceramic feedthrough substrate provides the electrical connections of the internal electronics board to both the nerve electrodes and percutaneous leads. In this paper, we will describe the various packaging components of the system and the design, fabrication, and assembly considerations that drove our technology choices.