Cavity Package Research Articles

Adhesive Solutions for Closed Cavity Packaging

The trend towards autonomous driving demands continuously increasing safety requirements and hence reliable components such as CMOS image sensors or communication devices. To provide such components, manufactures are facing ever greater challenges as the sensor packages need to be airtight sealed over their whole lifetime. Typical defects that can be observed when using conventional lid attach materials for closed cavity packages in tests at automotive level (e.g., according to AEC Q100) are pop-up effects and delamination. To avoid these defects and to meet the increasing reliability requirements of the semiconductor industry, DELO Industrial Adhesives has developed special adhesives that not only ensure reliable bonding while keeping narrow and high bondlines, but also improve process stability. Features such as light/heat B-stage or light fixation help to keep the attached lid in place during heat curing and other subsequent steps like temperature cycling, humidity storage and even reflow.

Adhesive Solutions for Closed Cavity Packaging

The trend towards autonomous driving demands continuously increasing safety requirements and hence reliable components such as CMOS image sensors or communication devices. To provide such components, manufactures are facing ever greater challenges as the sensor packages need to be airtight-sealed over its whole lifetime. Typical defects that can be observed when using conventional lid attach materials for closed cavity packages in tests at automotive level (e.g., according to AEC Q100) are pop-up effects and delamination. To avoid these defects and to meet the increasing reliability requirements of the semiconductor industry, DELO Industrial Adhesives has developed special adhesives that not only ensure reliable bonding while keeping narrow and high bondlines, but also improve process stability. The required adhesive properties were defined by an FE analysis model. To test suitability of the new developments, dummy image sensor packages were built up, which passed through the testing of the bearing, according to AEC Q 100 standard. Finally, the tightness of the bondline was checked via microscope and other methods. Features such as light/heat B-stage or light fixation help to keep the attached lid in place during heat curing and other subsequent steps like temperature cycling, humidity storage or reflow.

Solutions for Low Cost, Near Hermetic Air Cavity Packages

The introduction of 5G networks includes both Macro Cell and Multiple-input, Multiple-output (MIMO) systems. Unique plastic air cavity solutions are available for both system types that address the continuous need for cost reduction while meeting high-frequency requirements. For today’s Air Cavity applications, expensive hermetic packaging is no longer required. Near hermetic, low-cost plastic packaging is replacing expensive ceramic packages and thus providing customers with reduced costs and faster time to market. In the Macro Cell space GaN Power Amplifiers (PA) are ramping to high volume production in 5G networks. The use of a Plastic air cavity package along with a copper flange vs a CPC flange provides the lower costs than ceramic packages while delivering better performance compared to an overmolded solution. RJR provides the package sidewall that attaches to the flange. A lid composed of low-cost LCP (Liquid Crystal Polymer) attaches to the sidewall to complete the package assembly. Today’s Plastic air cavity, medium power package solutions can meet the requirements of Multiple-input, Multiple-output (MIMO) antenna arrays used in the 5G network, to be able to deliver high data rates to multiple users in dense urban areas. The package solution consists of a matrix lid panel that is attached to a populated PCB substrate. The packages described above are enabled with RJR proprietary B-stage epoxy. The use of the proper B-stage epoxy delivers a near-hermetic solution. The package assembly is completed by using a defined process technique that specifies time, temperature and pressure, that can utilize RJR’s Isothermal Seal Machines. This paper will provide insight on the plastic air cavity packages available for 5G applications along with reliability data and information on multi chip laminate solutions with a matrix air cavity lid that aids in lower assembly costs.

Next Generation High Powered RF and Optical Packages

RF signals are radio waves that are very crucial for telecommunications. Quality communications require reliable materials which are appropriately processed to house high-powered semiconductors such as GaN and GaAs. It is equally crucial to accommodate passive electronic components along with these semiconductors into the housings for the Next Generation RF package or GenPack™. Evolving semiconductor technologies demand fail-safe packages to protect the devices in all applications and environmental conditions. Future aircraft, EV cars, spacecraft, augmented and/ or virtual reality headsets, medical devices and many more technologies require operating at a higher power and frequency with a proper thermal and power management platform. The higher speeds of telecommunications hinge on the performance of semiconductors and their packages. Therefore, the GenPack™ and packaging process are becoming crucial pieces of the supply chain. Rugged GenPack™ RF packages differ in several ways compared to the traditional air cavity packages. For instance, FR-4 or Flame-Retardant glass-reinforced epoxy laminate material can be replaced with Aluminum Nitride or Alumina Oxide, Silicon Nitride or even Sapphire. The switch offers mechanical bonding directly onto the thermal spreader. Traditional circuits created on printed circuit boards have limited ability to dissipate heat due to the low thermal conductivity of FR4. Circuits created on ceramic can dissipate higher amounts of heat. As in the organic FR4 boards, multiple vias can be formed in the ceramic substrates to create metal pads top the ceramic that are grounded to the flange beneath the ceramic. A metal flange can be positioned beneath the ceramic to provide a heat spreader and electrical ground that can be bolted onto a heatsink. Flanges can be made from a diamond metal matrix composite instead of lower thermal conductivity materials to provide much more efficient thermal transfer. Furthermore, narrow leads offer optimized impedance at RF and microwave frequencies. A range of ceramic and flange materials can be selected to optimize GenPack™ RF Packages with cost, quality, and performance in considerations for the respective applications.

Single-Layer Evanescent Wave Absorbers in Rectangular Waveguides Based on Evanescent Mode Coupling and Attenuation

A microwave absorber for absorbing waves below the cutoff frequency of a rectangular waveguide (RWG) is proposed in this study. By loading an ideal lossy capacitive metasurface (LCMS) in the crosssection of an RWG close to the radiation source, the LCMS exhibits the ability to couple with and attenuate the waves below the cutoff frequency of the RWG, i.e., absorb the evanescent waves (EWs). The operating mechanism is analyzed with several parametric studies based on the momentum matching principle, and a systematic design procedure for a practical EW absorber is concluded. Three samples made of indium tin oxide thin films are designed, fabricated, and tested, and the experimental results agree well with the theoretical results. The maximum measured absorptance reaches up to 97%. Compared with conventional plane-wave absorbers with multilayer conductors, the proposed EW absorber only requires a single-layer conductor and has a distinct working mechanism, design principle, and application scenario. In the examples considered in this study, the samples can serve as the specific matching component for calibrating the RWG below the cutoff frequency. Notably, our EW absorption technique provides a feasible approach to suppress the electromagnetic interference dominated by the evanescent mode in the electrically small metallic cavity packages and near field of integrated circuits.

The influence of the water ingression and melt eruption model on the MELCOR code prediction of molten corium-concrete interaction in the APR-1400 reactor cavity

In the present study, the cavity module of the MELCOR code is used for the simulation of molten corium concrete interaction (MCCI) during the late phase of postulated large break loss of coolant (LB-LOCA) accident in the APR1400 reactor design. Using the molten corium composition data from previous MELCOR Simulation of APR1400 under LB-LOCA accident, the ex-vessel phases of the accident sequences with long-term MCCI are recalculated with stand-alone cavity package of the MELCOR code to investigate the impact of water ingression and melt eruption models which were hitherto absent in MELCOR code. Significant changes in the MCCI behaviors in terms of the heat transfer rates, amount of gases released, and maximum cavity ablation depths are observed and reported in this study. Most especially, the incorporation of these models in the new release of MELCOR code has led to the reduction of the maximum ablation depth in radial and axial directions by ∼38% and ∼32%, respectively. These impacts are substantial enough to change the conclusions earlier reached by researchers who had used the older versions of the MELCOR code for their studies. and it could also impact the estimated cost of the severe accident mitigation system in the APR1400 reactor.

High Frequency, Low Loss, Additively Manufactured Hermetic Package

Abstract This paper presents the development of a new type of hermetic cavity package for mmWave RF MMICs. The package features an all copper additively manufactured construction for optimal thermal performance as well as low loss air coax RF signal routing with a critical ceramic feedthrough to isolate the internals of the package from the external environment. With a simulated thermal resistance of 1 C/W, from die backside to package lid, and RF insertion loss of less than 0.5dB from 0–80Ghz, this package can support high power as well as high frequency MMICS. With no polymers in the construction of the package true hermetic performance is expected, making this package a high reliability option as well. For this paper two die were selected for demo packages. These die do not have surface mountable packages offered on the market. The die selected are the CMD247 30–40GHz Low Phase Noise Amplifier from Qorvo and the CHA2080-98F 71–86GHz Low Noise Amplifier from United Monolithic Semiconductors. RF insertion loss as well as environmental reliability will be demonstrated with these devices. The additive manufacturing process used is the proprietary PolyStrata® process developed by Nuvotronics. With the development of 14” panel substrate manufacturing line utilizing a mask-less process, fabrication process can support both high-volume, and high-customization without incurring prohibitive tooling costs.

Micro-fabricated alkali vapor cells sealed at low temperature using asymmetric Au–In transient liquid phase (TLP) bonding

Vapor cells as the key part of chip-scale atomic clocks determine their volume stability and power consumption. Micro-fabrication, especially the cavity packaging, is challenging. In this paper, micro-fabricated rubidium vapor cells are fabricated and the Au-In TLP bonding with asymmetric metal configuration is proposed and designed to package wafer-scale cell chips at a low processing temperature of 200 °C. Tests show that the designed intermetallic compounds AuIn2 and AuIn are uniformly formed in the asymmetric TLP bonding interlayer, indicating that the bonded interlayer can endure a post-processing temperature as high as 490 °C. The TLP bonded surface exhibits shear strength of 31.68 MPa, and the upper limit for the leak rate of the sealed vapor cell is 5 × 10−10 mbar · L s–1 which remains stable after undergoing a high temperature post-treatment. Meaning the proposed Au-In TLP bonding technique is applicable at low-temperature, hermetic and reliable wafer-scale packaging for micro-fabricated alkali vapor cells.

Characterization of a [formula omitted]=0.5 double spoke cavity with a fixed power coupler

ESS, the European Spallation Source, will adopt a single family of double spoke cavities for accelerating the beam from the normal conducting section to the first family of the elliptical superconducting cavities. It will be the first double spoke cavities in the world to be commissioned for a high power proton accelerator. The first double spoke cavity for the ESS project was tested with high power in the HNOSS cryostat at Uppsala University. A pulse-mode test stand based on a self-excited loop was used in this test. The qualification of the cavity package involves a double-spoke superconducting cavity, a fixed fundamental power coupler, tuner, a low-level radiofrequency (LLRF) system and a high-power radiofrequency (RF) station. The test represents an important verification milestone before the module assembly. This cavity had unfortunately a high dynamic loss of 12 W @ 9 MV/m, where potential causes for such a high value have been studied and corresponding suggestions are listed. This paper presents the test configuration, RF conditioning history, first high power performance and experience of this cavity package.

Flow Behavior Analysis of Emc in Molded Underfill (Muf) Encapsulation for Multi Flip-Chip Package

This paper present a numerical analysis of molded underfill (MUF) for multi flip chip package during encapsulation. Castro Macosko model is used in ANSYS fluent to describe the flow behavior of the EMC. The physical quantities such as viscosity, shear rate and velocity is plotted to analyzed the flow behavior of EMC during encapsulation. The EMC flow behavior at flip chip (FC) and free passage (FP) region in cavity are been compared. The viscosity profile of EMC is inversely proportional to the shear rate and velocity profile at FC and FP region The tendency of “frozen skin” layer occur in cavity package have been predicted with velocity profile during encapsulation.

Stencil Print solutions for Advance Packaging Applications

Abstract This paper address two significant applications of stencils in advance packaging field: 1. Ultra-Thin stencils for miniature component (0201m) assembly; 2. Deep Cavity stencils for embedded (open cavity) packaging. As the world of electronics continues to evolve with focus on smaller, lighter, faster, and feature-enhanced high-performing electronic products, so are the requirement for complex stencils to assemble such components. These stencil thicknesses start from less than 25um with apertures as small as 60um (or less). Step stencils are used when varying stencil thicknesses are required to print into cavities or on elevated surfaces or to provide relief for certain features on a board. In the early days of SMT assembly, step stencils were used to reduce the stencil thickness for 25 mil pitch leaded device apertures. Thick metal stencils that have both relief-etch pockets and reservoir step pockets are very useful for paste reservoir printing. Electroform Step-Up Stencils for ceramic BGA's and RF Shields are a good solution to achieve additional solder paste height on the pads of these components as well as providing exceptional paste transfer for smaller components like uBGAs and 0201s. As the components are getting smaller, for example 0201m, or as the available real estate for component placement on a board is getting smaller – finer is the aperture size and the pitch on the stencils. Aggressive distances from step wall to aperture are also required. Ultra-thin stencils with thicknesses in the order of 15um–40um with steps of 15um are used to obtain desired print volumes. Stencils with thickness to this order can be potential tools even to print for RDLs in the package. Cavity technology can be an effective solution in reducing the total assembled PCB thickness (Z-height), most importantly, on designs utilizing taller - stacked devices. Traditionally, dipping process or dispensing process was used to deposit solder paste, flux, or glue on uneven surfaces. However, this takes a longer time when compared to printing using a stencil printer. Reservoir printing using a stencil printer has greater potential in such application. Extensive work has been done in the past to print glue, solder paste and/or flux into cavities using reservoir printing. This paper focuses on printing solder paste into multiple cavities (stencil pockets) with depths ranging from 355 microns to 450 microns, and with varying cavity size, wall angles and various stencil thicknesses ranging from 100 microns to 150 microns. Apertures varying in area ratio were placed in these cavities and experiments were conducted to analyze the print performance of the stencils. As the size of the components and boards/substrates gets smaller - closer placement of components to the cavity (stencil pocket) walls needed to be assessed as well. These applications, the associated stencil design and print results were discussed in detail in this paper.

Modeling Vibration Induced Fatigue Failure of Free Standing Wire Bonds

Abstract Wire bonds are used to connect device terminals to package terminals or substrate terminal that forms circuits that are needed to create desired higher level functions. If a wire bond breaks or becomes detached during operation, the desired function will be lost. Depending on the design, a loss in function could be catastrophic. Aluminum, gold, and copper wires are used to create wire bonds in electronic products. These materials have been selected for their ability to be formed as fine wires and their ability to provide low electrical resistance. In many electronics packages, wire bonds are encapsulated in a polymer molding compound that is used to protect the electronic device. However, in some electronic devices such as hermetically sealed cavity packages, wire bonds may be free-standing. Under vibration loading, free-standing wire bonds may be subject to failure due to mechanical fatigue. In this work, an analytic model is presented for predicting natural frequency of a free-standing wire bond and for assessing a wire bond time to failure under a harmonic loading condition. The model for natural frequency is calibrated by finite element analysis and validated through experimental testing. The life prediction model, a test plan, and preliminary test results are presented.

Validation of the superconducting 3.9 GHz cavity package for the European X-ray Free Electron Laser

A full test of the cavity package concept under realistic operating condition was a necessary step before the assembly of the European XFEL (EXFEL) 3.9 GHz superconducting system and its installation in the accelerator. One cavity, equipped with magnetic shielding, power coupler and frequency tuner has been tested in a specially designed single cavity cryostat in one of the test benches of the DESY Accelerator Module Test Facility (AMTF). The cavity was operated at high pulsed power up to an accelerating field of $24\text{ }\text{ }\mathrm{MV}/\mathrm{m}$, above the quench accelerating field of $21\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ achieved during the continuous wave (CW) vertical qualification test and with a large margin with respect to the EXFEL maximum operating specification of $15\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ for the 3.9 GHz system. All subsystems under test---coupler, tuner, waveguide tuners, low level radio-frequency (LLRF) system---were qualified to their design performances.

Low-power motion gesture sensor with a partially open cavity package.

In an IR proximity-based motion gesture sensor (MGS) mainly composed of an IR LED and photodiodes (PDs), the IR LED is the most power-hungry component. For reducing its power, both the size and the field-of-view (FOV) of each PD can be increased instead. However, it cannot be adapted to conventional MGSs due to the geometrical limitation of their optical structures. In this paper, the optical structure of the proposed MGS with a partially open cavity package allows for power reduction by at least 70.9% compared with conventional MGSs. Optical simulation and test results validate the theoretical analysis presented.

A THz Detector Chip With Printed Circular Cavity as Package and Enhancement of Antenna Gain

A terahertz (THz) detector chip with a low-cost printed circular cavity package is proposed in this article. The chip consists of a differentially fed antenna and a Schottky diode at its terminal. The passive structure of the Schottky diode is modeled into the antenna. To improve its performance, the detectenna ( ${\text{detector}} + {\text{antenna}}$ ) chip is designed so that it can be mounted on the upper side of a Duroid substrate with a metal strip ring surrounding the chip. The ring is connected to the ground plane on the bottom of the substrate by vias to form a circular cavity. With the so-called circular cavity package, the radiation pattern of the antenna on the chip is not only converted from omnidirectional to unidirectional, but also with its surface wave well suppressed, the directivity of the antenna can increase, and hence improve its sensitivity. With this cavity, the isolation between adjacent elements can also be improved if it is used to build an array. The measured results show that a gain enhancement of $5.4{-}7.7\,{\text{dB}}$ can be achieved within the operating bandwidth. The maximum sensitivity is $563\,{\text {V}}/({\text {W}}/{\text{mm}}^{2})$ and the minimum noise equivalent power density (NEPD) is $1.2({\text{pW}}/{\text{mm}}^{2})/({\text{Hz}})^{1/2}$ at 216 GHz.

Unconventional Use of a Photoresist as a Nitrogen Gas Generator Forming Transparent Dome‐Shaped Microcavities

The phenomenon that a common positive photoresist (PR) releases nitrogen (N2) gas when exposed to UV light has never been used or received any particular attention. Fabrication process to intentionally trap the generated N2 gas during UV exposure, thereby, to form the microcavity structure is proposed. Various dome‐shaped structures are demonstrated with the proposed process. This process is best suited to make various cavity packages in microelectromechanical systems. Also, microlens arrays are fabricated using plastic replication of the dome‐shaped microcavities. All these results lead to a different view of the conventional positive photoresist and inspire various new applications.

Liquid Crystal Polymer for QFN packaging: Predicted thermo-mechanical fatigue and Design for Reliability

Thermoplastic resins, such as Liquid Crystal Polymers (LCPs), have many attractive properties for microelectronic cavity package manufacturing (in particular low gas permeation and low dielectric constant). In order to reduce anisotropic mechanical properties inducing a potential fragility of the material and then a lack of reliability of the package, various approaches are currently studied in particular the addition of mineral fillers. A dedicated Design of Experiments (DoE) is performed to assess the optimal thermo-mechanical properties of the LCP compound and then the optimal composition of the package leading to the maximum operating lifetime. In this way the long-term reliability of an electronic package (Quad Flat No-lead – QFN – package) based on various formulations of the LCP composite is assessed by thermo-mechanical simulation using Finite Element Method (FEM). A Design for Reliability (DfR) methodology is proposed according to the simulation results based on Taguchi methodology. This methodology allows the determination of the optimal composition (nature/proportion/size/chemical functionalization of fillers) of the LCP package by reducing the number of experimental studies that are very time consuming.

Technologies for Wafer Level MEMS Capping based on Permanent and Temporary Wafer Bonding

Further cost reduction and miniaturization of electronic systems requires new concepts for highly efficient packaging of MEMS components like RF resonators or switches, quartz crystals, bolometers, BAWs etc. This paper describes suitable base technologies for the miniaturized, low-cost wafer level chip-scale packaging of such MEMS. The approaches are based on temporary handling and permanent bonding of cap structures using adhesives or solder onto passive or active silicon wafers which are populated with MEMS components or the MEMS wafer themselves. Firstly, an overview of the possible packaging configurations based on different types of MEMS is discussed where TSV based and non-TSV based packaging solutions are distinguished in general. The cap structure for the TSV based solution can have the same size as the MEMS carrying substrate, since the electrical contacts for the MEMS can be routed either thought the cap or base substrate. Thus, full format cap wafers can be used in a regular wafer to wafer bonding process to create the wafer level cavity packages. However, if no TSVs are present in the cap or base substrate, the cap structure needs to be smaller than the base chip, so that electrical contacts outside the cap area can be accessed after the caps were bonded. Such a wafer level capping with caps smaller than the corresponding base chips can be obtained in two ways. The first approach is based on fabrication and singulation of the caps followed by their temporary face up assembly in the desired pattern on a help wafer. In a subsequent wafer to wafer bonding sequence all caps are transferred onto the base wafer. Finally the help wafer is removed from the back side of the bonded caps. This approach of reconfigured wafer bonding is especially used for uniform cap patterns or, if MEMS have an own bond frame structure. In that case no additional cap is required, since the MEMS can act as their own cap. The second approach is based on cap structure fabrication using a compound wafer stack consisting of two temporary bonded wafers. One wafer acts as carrier wafer whereas the other wafer is processed to form cap structures. Processes like thinning, silicon dry etching, deposition and structuring of polymer or metal bonding frames are performed to generate free-standing and face-up directed cap structures. The so created “cap donor wafer” is used in a wafer to wafer bonding process to bond all caps permanently to the corresponding MEMS base wafer. Finally, the temporary bonded carrier wafer is removed from the backside of the transferred caps. With that approach a fully custom specific and selective wafer level capping is possible featuring irregular cap patterns and locations on the MEMS base wafer. Examples like the selective capping process for RF MEMS switches are presented and discussed in detail. All processes were performed at 200mm wafer level.

“Has Microelectronic MCM Technology Matured and is it Capable of Servicing the Widespread Needs of Down Well 225°C Operating Applications in the Oil and Gas Industry?”

This paper reviews development and qualification work performed on 225°C operating temperature modules based on ceramic thick film multi-layer substrates supporting embedded thick film resistors, assembled passive and active components with ‘chip and wire’ connections and sealing in hermetic metal and ceramic cavity packages. It considers aspects of development and importantly investigates product qualification which includes shock and vibration at elevated temperatures as well as thermal shock and temperature cycling. In conclusion there is an attempt to answer the question “Has microelectronic MCM technology matured and is it capable of servicing the widespread needs of down well 225 °C operating applications in the Oil and Gas industry?”

Adhesive Wafer Bonding Applied for Fabrication of True-Chip-Size Packages for SAW Devices

Surface Acoustic Wave (SAW) filters are key components for mobile communication. In SAW devices mechanical waves propagate on the surface of a piezoelectric bulk material such as LiNbO3 or LiTaO3. SAW components require advanced cavity packaging solutions in order to enable the mechanical wave propagation on the substrate material. Size reduction of SAW filters allows further miniaturization of mobile phones and an extension of their functionality. The mobile communication industry, therefore, demands advanced cavity package technologies to be developed for SAW components. These packages have to offer high performance, high reliability, and low cost while maintaining a form factor as small as possible. To address these requirements EPCOS has developed a Die Sized SAW Package (DSSP), a true chip-size wafer level package for SAW filters. This paper discusses the manufacturing process of wafer-level-packages for SAW-devices with a special focus on the adhesive wafer bonding technology.