Low Temperature Co-fired Ceramic Module Research Articles

In-Line Vector Modulator Integration in Dielectric-Filled Waveguide

This paper proposes a scalable substrate-integrated waveguide (SIW) module accommodating an in-line vector modulator monolithic millimeter integrated circuit (MMIC). The SIW module is realized with low-temperature co-fired ceramic (LTCC) technology, and it can be inserted in a dielectric-filled waveguide (DFWG). The module combines λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>g</i></sub> /4-transformer-based E-plane tapering and SIWs on LTCC with the wire-bonded vector modulator. The proposed active LTCC module and two passive test structures (i.e., a constant-height-SIW module and a SIW module with E-plane taperings) are manufactured and tested as in-line modules in a DFWG. The passive test structures with the waveguide-to-DFWG and DFWG-to-SIW transitions measure 3.1 dB and 4.6 dB of insertion loss on average, respectively, at the 71–81 GHz frequency range. The active LTCC module measurements demonstrate a dielectric-filled waveguide with phase and amplitude tuning capability and gain up to 17.6 dB within the same frequency range. A four-channel mock-up module with λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /2 channel spacing is designed and manufactured to demonstrate the scalability of the design.

Metallization, Material Selection, and Bonding of Interconnections for Novel LTCC and HTCC Power Modules.

Ceramic baseplates are important elements in the power modules of electric drives. This paper presents low-temperature cofired ceramic (LTCC) and high-temperature cofired ceramic (HTCC) materials for the fabrication of three-dimensional power modules. The silver-based metallization and power module assembly are presented, together with aluminum-based power wire bonding and an industrial procedure to achieve high solderability and bondability. The results of the bond tests using different metallization materials, especially cost-effective ones, are presented, together with the assembly of the power modules. The best results were achieved with Ag metallization and 380 µm Al wire and with Ag–Pd metallization and 25 µm Al wire, both on an LTCC base. The paper concludes with a dual-pulse electrical test of the power modules, which proves the quality of metallization, the type of material selected, and the correctness of the wire bonding and assembly.

Cooling of electronic components on the LTCC module with an embedded flat heat pipe

The results of the experimental investigations of a ceramic circuit board sample with an embedded flat heat pipe are presented. The sample was made based on the technology of low temperature co-fired ceramic (LTCC). The flat heat pipe is formed at the bottom side of a ceramic substrate using a capillary structure made of sintered copper powder. The developed prototype of the LTCC module was used for the investigation of removing and spreading of high heat fluxes from high power electronic components mounted on the module. The embedded flat heat pipe filled with acetone provides 40 W/cm2 of heat flux removal from the heat source with the heat dissipation area of 1 cm2. The measured value of the thermal resistance between the heat source and cooler surface under the module is 0.8 °C/W.

A Wide-Angle Scanning Switched-Beam Antenna System in LTCC Technology With High Beam Crossing Levels for V-Band Communications

Wide-angle coverage, fine angular resolution, and low-power consumption are the key characteristics of millimeter-wave short-range wireless systems, such as access points in fifth-generation cellular networks and automotive radars. In this paper, we present a 60 GHz switched-beam antenna system addressing all these requirements. It consists of two identical parallel-fed arrays of eight slots, each fed by a passive pillbox beamformer. A switch network comprising four single-pole-multiple-throw switches excites one of the two arrays at a time and selects the radiated beam. The whole system is fully integrated into a multilayer low-temperature cofired ceramic module. The antenna covers a scan range of about ±39° in one plane using 11 beams between 57 and 66 GHz. The proposed architecture enables the simultaneous achievement of continuous coverage (beam crossover levels of about −3 dB) and of low sidelobe levels. Dedicated numerical tools are used for a preliminary design of the antenna. The design procedure, the technological development, and the experimental results are discussed in detail.

The Relevance of Low Temperature Co-fired Ceramic Module Packaging in the 5G Market

Abstract 5th Generation Telecommunications Technology, 5G, is emerging to provide the market with even higher data rates and bandwidth and lower response times than the 4th generation telecommunications technology, 4G/LTE, that is currently deployed. With commercial 5G networks coming on-line in 2020 the network providers and infrastructure companies are quickly developing devices and systems to meet the demand of the 5G market. Since high data rates and high bandwidths demand high frequency microwave, MW, devices, Low-Temperature Co-fired Ceramic, LTCC, is one of the materials of choice for those modules in a 5G system that require the high 3D integration, high signal integrity, high reliability and high power performance of LTCC. LTCC has proven for more than two decades now to exhibit these qualities in high-frequency telecommunication applications. This paper explores the relevance of LTCC technology in the module packaging market in the 5G market.

An Integrated Low Temperature Co-Fired Ceramic-Based Clark-Type Oxygen Sensor

Low temperature co-fired ceramic (LTCC) electronic packaging materials are applied for the advantages of their mechanical durability, low cost, flexibility of the layered manufacturing, and capability to integrate both electronic and microfluidic functions in a single LTCC module. Clark-type oxygen sensors are electrochemical devices that are widely used for sensing dissolved oxygen in biological applications. In this paper, a Clark-type oxygen sensor has been developed using the LTCC thick-film technique instead of the traditional silicone/glass micromachining, and it consisted of an LTCC substrate with three electrodes (working electrode, counter electrode, and Ag/AgCl reference electrode), a polydimethylsiloxane (PDMS) oxygen permeable membrane and a PDMS reservoir. The fabricated Ag/AgCl reference electrode demonstrated high density with longtime stability. Cyclic voltammetry and chronoamperometry were measured to evaluate the electrochemical properties of the LTCC-based Clark-type oxygen sensor. The reduction current had a linear relationship with oxygen concentration. Meanwhile, the LTCC-based Clark-type oxygen sensor exhibited comparative performances, including low residual current, <5%, and fast response time, 7.5 s, compared with the literatures.

CuO/V2O5-Codoped Bi3/2ZnNb3/2O7 (BZN) Ceramic for Embedded Capacitor Layer in Integrated LTCC Modules

Sintering additives for Bi3/2ZnNb3/2O7 (BZN) ceramic have been studied to facilitate use of BZN as a material for embedded decoupling capacitors in high-density multilayered low-temperature cofired ceramic (LTCC) modules for mobile communication systems and three-dimensional printing modules. Among the additives studied, a CuO/V2O5 mixture was the most promising for cofiring BZN ceramic with a commercial low-permittivity (e r) LTCC sheet (MLS-22; NEG Co., Japan) and Ag electrode. BZN codoped with 0.5 wt.% CuO/V2O5 was successfully densified at 860°C by reactive liquid-phase sintering, and the resulting dielectric properties were acceptable for use of the CuO/V2O5-codoped BZN for embedded capacitors in LTCC modules. The room-temperature permittivity (e r) of the CuO/V2O5-codoped BZN was 148 at 1 MHz, and the capacitance thermal stability was ±1.3% within the temperature range of −55°C to 125°C. The physical and chemical compatibilities of the CuO/V2O5-codoped BZN with heterogeneous layers (low-e r LTCC layer and Ag electrode layer) in LTCC modules were also examined. A cofiring test of the doped BZN ceramic with MLS-22 LTCC sheet revealed that thickness control of the two heterogeneous layers was a key factor to avoid crack formation during cofiring. The optimum thickness ratio of doped BZN to MLS-22 layers was less than 0.25:1. A chemical compatibility test revealed no severe reaction between the doped BZN/MLS-22 and doped BZN/Ag layers.

BPF integrated amplifier module using LTCC technology for millimeter‐wave applications

ABSTRACTA compact amplifier module integrating a low‐loss stripline (SL) band‐pass filter (BPF) using low‐temperature cofired ceramic (LTCC) technology is presented for millimeter‐wave (mm‐wave) applications. A parasitic resonance‐free SL BPF is proposed by modifying a distribution of ground vias in the SL LTCC BPF. The SL BPF fabricated in the 6 LTCC layers showed a 3‐dB bandwidth of 8.4% at the center frequency of 41.8 GHz. Its measured insertion and return loss were as small as 1.7 dB and 10.2 dB, respectively. The SL BPF integrated amplifier LTCC module was implemented in the single LTCC substrate in a size of 11.3 × 12.2 × 0.6 mm3. Its gain of 10 dB and output power of 18 dBm is achieved in the pass band from 39.5 to 42 GHz. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1821–1825, 2015

Lifetime prediction and design aspects of reliable lead-free non-collapsible BGA joints in LTCC packages for RF/microwave telecommunication applications

Purpose – The purpose of this paper is to describe the behavior of different lead-free solders (95.5Sn3.8Ag0.7Cu, i.e. SAC387 and Sn7In4.1Ag0.5Cu, i.e. SAC-In) in thermomechanically loaded non-collapsible ball grid array (BGA) joints of a low-temperature co-fired ceramic (LTCC) module. The validity of a modified Engelmaier’s model was tested to verify its capability to predict the characteristic lifetime of an LTCC module assembly implementable in field applications. Design/methodology/approach – Five printed wiring board (PWB) assemblies, each carrying eight LTCC modules, were fabricated and exposed to a temperature cycling test over a −40 to 125°C temperature range to determine the characteristic lifetimes of interconnections in the LTCC module/PWB assemblies. The failure mechanisms of the test assemblies were verified using scanning acoustic microscopy, scanning electron microscopy (SEM) and field emission SEM investigation. A stress-dependent Engelmaier’s model, adjusted for plastic-core solder ball (PCSB) BGA structures, was used to predict the characteristic lifetimes of the assemblies. Findings – Depending on the joint configuration, characteristic lifetimes of up to 1,920 cycles were achieved in the thermal cycling testing. The results showed that intergranular (creep) failures occurred primarily only in the joints containing Sn7In4.1Ag0.5Cu solder. Other primary failure mechanisms (mixed transgranular/intergranular, separation of the intermetallic compound/solder interface and cracking in the interface between the ceramic and metallization) were observed in the other joint configurations. The modified Engelmaier’s model was found to predict the lifetime of interconnections with good accuracy. The results confirmed the superiority of SAC-In solder over SAC in terms of reliability, and also proved that an air cavity structure of the module, which enhances its radio frequency (RF) performance, did not degrade the reliability of the second-level interconnections of the test assemblies. Originality/value – This paper shows the superiority of SAC-In solder over SAC387 solder in terms of reliability and verifies the applicability of the modified Engelmaier’s model as an accurate lifetime prediction method for PCSB BGA structures for the presented LTCC packages for RF/microwave telecommunication applications.

Electrooptic Inspection of Vector Leakage in Radiofrequency Multichip Modules

This paper demonstrates a new approach for the measurement of vector electromagnetic leakage within tightly integrated electronic subsystems. Specifically, the effect of shielding and encapsulation techniques commonly used in radiofrequency (RF) multichip modules is investigated using an electrooptic (EO) near-field measurement system. The test vehicle used for this study is a single-chip 50-W microwave power amplifier integrated into a multilayer low-temperature cofired ceramic module. The measured near-field data show power intensity at 2.5 GHz with up to 0.2-mm resolution for each of the three x-, y-, and z-directed electric field vectors. The resulting images illustrate 1) the polarization-dependent shortcomings of the ubiquitous “via-fence” shielding technique and 2) the formation of surface waves in microstrip substrates due to impedance mismatch. These results are evidence of the applicability of the EO technique to the diagnosis of electromagnetic compatibility issues within compact RF multichip modules.

OPTIMIZATION OF SHRINKAGE AND SURFACE-ROUGHNESS OF LTCC TAPE

The Low Temperature Co-fired Ceramics (LTCC) proces s is very popular in the electronics packaging indu stry and is broadly accepted for its low cost and rapid throughput. A m ultilayer LTCC 3-D structure generally shrinks duri ng low temperature co-firing process. Shrinkage occurs in all three dimensions X , Y and Z. Shrinkage has added a challenge to get h igh performance with low temperature co-fired ceramics designs and limited t he yields of LTCC modules, components, subsystems aRoughness is the measure of texture of surface of LTCC tape and a qu antitative analysis of vertical deviation of real surface from its ideal form. This paper describes variations in X, Y and Z direc tions of LTCC tape during firing at different tempe ratures and also describes about the surface roughness of LTCC tape. Data has been con the experimental results and observa tions.

Design and fabrication of a valveless micropump based on low temperature co-fired ceramic tape technology

Low temperature co-fired ceramic (LTCC) tape technology has been widely studied in microsystems and microfluidic devices. The current study presented the manufacturing process of a simple and inexpensive micropump which is made of LTCC. The components of micropump including fluidic channels, diaphragm, chamber, and planar diffuser valves were integrated in one LTCC module. Geometries of these components were designed based on numerical analysis. The finite element analysis was used to characterize the displacement of a piezoelectric actuator and the computational fluid dynamics was applied to design the diffuser. The performance of the micropump was optimized and performance of the designed micropump was carefully examined in the experiments. The data revealed that the performance of a micropump can be significantly increased by adding a pair of pockets. Overall, the study demonstrated that LTCC tape technology is a simple and reliable method to fabricate a valveless micropump.

Reliability of SMD interconnections on flexible low-temperature substrates with inkjet-printed conductors

This work dealt with potential reliability issues in inkjet-printed electronics. The aim was to increase our understanding of how failures occur in hybrid electronic structures that utilize inkjet printing. A future goal in this field will be to enable expansion of this product area from low-life-expectancy and -performance products to high-life-expectancy and -performance products.In this work the reliability of isotropically conductive adhesive interconnections between 0402- and 0805-sized ceramic resistors and three types of flexible substrates was investigated. The use of low-temperature ink material (curing temperature 150°C) allows new, inexpensive substrates to be introduced into the process. In addition, the interconnection reliability of a more complex low-temperature cofired ceramic module attached to a flexible substrate with ball grid array interconnections was investigated.Reliability testing was carried out in a thermal cycling test chamber in a 0–100°C temperature range. Daisy-chain resistances of the samples were monitored with a datalogger during the cycling. Besides optical inspections, the interconnections were analyzed with X-ray microscopy. Also scanning acoustic microscopy was used to observe crack propagation. Finally, scanning electron microscopy was used to detect failure mechanisms.The two main failure mechanisms of the chip resistor components were loss of adhesion at the ICA/component terminal cladding interface and cracking of matte tin cladding of the component. For the tested LTCCs it was noted that breakdowns of interconnections occurred because of fractures on the module side of the interconnection—in most cases in the solder/intermetallic compound interface—and not because of ICA fractures or ink delamination on the substrate side.

Localized Temperature Stability in Low‐Temperature Cofired Ceramics

Low‐temperature cofired ceramic (LTCC) is a multilayer 3D packaging, interconnection, and integration technology. For LTCC modules targeting radio and microwave frequency (RF and MW) applications, a low or near 0 ppm/°C temperature coefficient of resonant frequency (τf) ensures temperature stability of embedded resonator and filter functions. The base dielectrics of most commercial LTCC systems have a τf in the range −50 to −80 ppm/°C. This study explored a method to achieve a zero τf on stripline (SL) resonators by locally cofiring, in a multilayer LTCC structure, compensating dielectrics (CD) with an opposite τf to that of the host dielectric. The formulation, synthesis, dielectric properties, and microstructure of SrTiO3 (STO)‐based low‐fire τf CD are presented. Chemical interactions and physical compatibility between the compensating and the host LTCC dielectrics are investigated for cofireability. The dependence of τf compensation on the wt% of STO, the printed thickness, and the location of the CD in multilayer LTCC are discussed. The most effective τf compensation is achieved by integrating CD next to the resonator lines, and can be explained by the concentration of electromagnetic energy via total internal reflection of electromagnetic waves inside the CD layer.

A miniature frequency-stabilized VCSEL system emitting at 795 nm based on LTCC modules

We present a compact frequency-stabilized laser system locked to the Rubidium absorption line of a micro-fabricated reference cell. A printed circuit board (PCB) is used to carry all the components and part of the electronics, and low-temperature co-fired ceramic (LTCC) modules are used to temperature-stabilize the laser diode and the miniature Rubidium cell (cell inner dimensions: 5mm diameter and 2mm height). The measured frequency stability of the laser, in terms of Allan deviation, is ≤8×10−10 for integration times of 103–105s. The current overall dimensions of the system are 70×40×50mm3, with good potential for realization of a frequency-stabilized laser module with few cm3 volume.

60-GHz Four-Element Phased-Array Transmit/Receive System-in-Package Using Phase Compensation Techniques in 65-nm Flip-Chip CMOS Process

AThe 60-GHz four-element phased-array transmit/receive (TX/RX) system-in-package antenna modules with phase-compensated techniques in 65-nm CMOS technology are presented. The design is based on the all-RF architecture with 4-bit RF switched LC phase shifters, phase compensated variable gain amplifier (VGA), 4:1 Wilkinson power combining/dividing network, variable-gain low-noise amplifier, power amplifier, 6-bit unary digital-to-analog converter, bias circuit, electrostatic discharge protection, and digital control interface (DCI). The 2 × 2 TX/RX phased arrays have been packaged with four antennas in low-temperature co-fired ceramic modules through flip-chip bonding and underfill process, and phased-array beam steering have been demonstrated. The entire beam-steering functions are digitally controllable, and individual registers are integrated at each front-end to enable beam steering through the DCI. The four-element TX array results in an output of 5 dBm per channel. The four-element RX array results in an average gain of 25 dB per channel. The four-element array consumes 400 mW in TX and 180 mW in RX and occupies an area of 3.74 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in the TX integrated circuit (IC) and 4.18 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> in the RX IC. The beam-steering measurement results show acceptable agreement of the synthesized and measured array pattern.

Localized Temperature Stability in Multilayer LTCC

Low temperature cofired ceramic (LTCC) is a multilayer 3D packaging, interconnection, and integration technology. One of the advantages of LTCC is the ability it affords to integrate passive components via the cofiring processes. For LTCC modules with embedded resonator functions targeting high frequency applications, the temperature coefficient of resonant frequency (τf) is a critical parameter. The base dielectrics of commercial LTCC systems have a τf in the range of −50 ppm/°C to −80 ppm/°C. This study explores a method to achieve zero or near zero τf embedded resonators by incorporating τf compensating materials locally into a multilayer LTCC structure. Chemical interactions and physical compatibility between the τf modifiers and the host LTCC dielectrics are investigated. A stripline (SL) ring resonator with near zero τf is demonstrated in a nonzero τf commercial LTCC.

Dispensing and hermetic sealing Rb in a miniature reference cell for integrated atomic clocks

An innovative method for fabricating the reference cell for a Rubidium (Rb) integrated atomic clock is presented. This method uses low-temperature solder sealing technique for producing mini-cells of the size of 14mm×10mm×3mm, suitable for Rb miniature atomic clocks. Top and bottom of the cell consists of two glass slides. An LTCC (low-temperature cofired ceramic) module of 2mm thickness, equipped with a small reservoir for confining the Rb is placed in between the two walls, acting as a spacer, increasing the total volume of the cell. A solder ring joins together the LTCC and the top of the cell. This paper also presents a new technique for handling the Rb, which allows its safe handling and long storage. The alkali metal is stored inside a pool of dodecane, which protects it from oxidation. Pure liquid Rb is then dispensed inside the adjacent reservoir using a glass micropipette; finally, the cell is heated in vacuum, in order to carry out the sealing. The achieved sealing hermeticity was tested, without Rb, by sealing N2O gas and monitoring its pressure through absorbance measurements using FTIR spectroscopy. Hermeticity was also tested with Rb by integrating a pressure sensor in the LTCC module.

Enhanced thermal fatigue endurance and lifetime prediction of lead‐free LGA joints in LTCC modules

PurposeThe purpose of this paper is to describe the effect of indium alloying on the thermal fatigue endurance of Sn3.8Ag0.7Cu solder in low‐temperature co‐fired ceramic (LTCC) modules with land grid array (LGA) joints and the feasibility of using a recalibrated Engelmaier model to predict the lifetime of LGA joints as determined with a test assembly.Design/methodology/approachTest assemblies were fabricated and exposed to a temperature cycling test over a temperature range of −40‐125°C. Organic printed wiring board (PWB) material with a low coefficient of thermal expansion was used to reduce the global thermal mismatch of the assembly. The characteristic lifetime, θ, of the test assemblies was determined using direct current resistance measurements. The metallurgy and failure mechanisms of the interconnections were verified using scanning acoustic microscopy, an optical microscope with polarized light, and scanning electron microscopy/energy dispersive spectrometry (SEM/EDS) investigations. Lifetime predictions of the test assemblies were calculated using the recalibrated Engelmaier model.FindingsThis work showed that indium alloying increased the characteristic lifetime of LGA joints by 15 percent compared with Sn3.8Ag0.7Cu joints. SEM/EDS analysis showed that alloying changed the composition, size, and distribution of intermetallic compounds within the solder matrix. It was also observed that a solid‐state phase transformation (Cu,Ni)6Sn5(→ (Ni,Cu)3Sn4 occurred at the Ni/(Cu,Ni)6Sn5 interface. Moreover, the results pointed out that individual recalibration curves for ceramic package/PWB assemblies with high (≥ 10 ppm/°C) and low (≈ 3‐4 ppm/°C) global thermal mismatches and different package thicknesses should be determined before the lifetime of LGA‐type assemblies can be predicted accurately using the recalibrated Engelmaier model.Originality/valueThe results proved that indium alloying of LGA joints can be done using In‐containing solder on pre‐tinned pads of an LTCC module, despite the different liquidus temperatures of the In‐containing and Sn3.8Ag0.7Cu solders. The characteristic metallurgical features and enhanced thermal fatigue endurance of the In‐alloyed SnAgCu joints were also determined. Finally, this work demonstrated the problems that exist in predicting the lifetime of ceramic packages with LGA joints using analytical modeling, and proposals for developing the recalibrated Engelmaier model to achieve more accurate results with different ceramic packages/PWB assemblies are given.

60-GHz Millimeter-Wave Identification Reader on 90-nm CMOS and LTCC

A reader module at 60 GHz for high data-rate short-range backscattering-based communications is presented. The reader consists of a CMOS-based oscillator, amplifiers, and a mixer on a low-temperature co-fired ceramic (LTCC) substrate. The filter, power splitter, and antennas are directly patterned on the LTCC. All millimeter-wave components are contained within the module and the only interfaces to the module are the IF and bias lines. Transmit power of the module is +11.6-dBm effective isotropic radiated power with an IF bandwidth of 400 MHz. The LTCC module measures 13×24 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and has a dc power consumption of 130 mW. Reception of a 20-MHz square wave from a tag 5 cm apart from the reader is demonstrated; the suggested millimeter-wave identification concept enables a 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> - 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> -fold data-rate increase in comparison to the present near-field communication technique, with similar size, range, and power consumption of the reader.