Low-temperature Co-fired Ceramic Package Research Articles

Preparation of an environment-friendly LTCC material by using waste soda-lime glass and natural volcanic ash

Glass/ceramic composites applied in the field of low-temperature co-fired ceramics (LTCC) were successfully prepared at 670–710 °C by using waste soda-lime glass (WG) as a binder and natural volcanic ash as a ceramic raw material. Based on the theories of suppression and supplementary network effects, alkaline-earth metal ions (R2+, R = Mg, Ca, Sr, and Ba) and B2O3 were applied to improve the dielectric properties of WG and composites, respectively. The influence of R2+ on the crystal phase evolution, microstructure, mechanical, dielectric, and thermal properties of WG-volcanic ash-based composites were systematically investigated. By doping 2.5 wt% Ba2+ to the environment-friendly LTCC composites, physical properties i.e., εr of 4.86 at 1 MHz, tan δ of 6.32 × 10−3, coefficient of thermal expansion of 8.72 × 10−6/°C, and thermal conductivity of 1.04 W/(m·K) are obtained. It is worth mentioning that the environment-friendly LTCC composite uses WG with a low glass transition temperature to reduce the sintering temperature and a tiny amount of a modifier to adjust the dielectric performance instead of synthesizing specific crystals by adding lots of chemical reagents. These, in turn, do not only have the potential to be used in the LTCC packaging technology but also have significance for sustainable development. Additionally, because of good chemical compatibility between aluminum and the composites, the environment-friendly LTCC composites with ultra-low sintering temperature have the potential ability to lower the cost of LTCC packaging materials.

Millimeter-Wave Wideband Dual-Polarized LTCC Antenna Array Based on Metasurfaces for Beam-Scanning Applications

This communication presents a millimeter-wave wideband dual-polarized low-temperature cofired ceramics (LTCC) antenna array based on metasurfaces (MSs) for beam-scanning applications. Benefiting from the wideband and large-freedom property of MS-based structures, a novel ±45° dual-polarized wideband MS-based antenna (MSA) element with high isolation is designed. The antenna element is fed by two orthogonal striplines on different layers, through a crosslike dog-bone slot and a narrow slot, respectively, to realize the two polarizations. The feeding structure consists of slot–stripline–slot–stripline from top to bottom and is specially designed to improve the polarization isolation of the antenna element. The proposed MSA element is compactly arranged with a small distance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ &lt; 0.5\lambda$ </tex-math></inline-formula> ) to construct a 4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 4 array integrated in an LTCC package, where via walls with metal ring strips are loaded between adjacent elements to reduce the gain fluctuation. Consequently, the array can achieve a good beam-scanning capability over a wide band of 19.5% with a maximum scanning angle up to ±55° and a small gain variation of less than 3 dB. Meanwhile, the active <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> parameters almost always remain below −10 dB, enabling good impedance matching when scanning at all angles. With these features, the proposed design has potential for application in 5G base-station systems.

Elevated temperature impact on performance of Low Temperature Co‐fired Ceramic dielectrics

AbstractThe need for electronics to operate at temperatures of 200°C and above continues to grow. These applications include avionics, aerospace, automotive, downhole drilling, mining, and many others. To satisfy this demand, a significant amount of research and development has been conducted. Despite the efforts, the number of new electronic components designed specifically for high‐temperature operation is still relatively limited. In Low Temperature Co‐fired Ceramic (LTCC) packages, LTCC materials are generally used as the host media for a number of pre‐fabricated semiconductor components. As a result, reliability of the entire LTCC package largely depends on the performance of the least robust component. Ferro A6M‐E and Ferro L8 are the two well‐established and recognized LTCC dielectrics widely used for mid and high frequency LTCC applications, including several high reliability aerospace and defense applications that require demanding Mil‐Spec qualifications. This study is our first attempt to characterize and understand basic high‐temperature dielectric properties of these two commercial LTCC materials. The secondary objective is to initiate a dialogue in attempt to establish reliability requirements for LTCC packages dedicated for high‐temperature operation.

Packaging Solution Based on Low-Temperature Cofired Ceramic Technology for Frequencies Beyond 100 GHz

In this paper, a package concept based on low-temperature cofired ceramic (LTCC) technology is illustrated. The concept is specifically designed for frequencies beyond 100 GHz, taking into consideration the inherent LTCC manufacturing defects, e.g., shrinkage, layer misalignment, and warping. Simple techniques are used for package assembly which can be automated using standard industrial processes. The proposed concept is implemented by integrating a 122-GHz silicon-germanium (SiGe) radar transceiver chip in an LTCC-based package. The off-chip components of the package, operating at 122 GHz, include a transmit (Tx) and a receive (Rx) aperture-coupled patch antenna array, a stripline to grounded coplanar waveguide signal transition feeding each of the antenna arrays, and three parallel, self-matched ground-signal-ground wirebonds connecting the SiGe radar transceiver chip and the LTCC package on Tx and Rx side. The simulation and measurement results of the Tx and Rx antenna arrays along with the signal transitions in the frequency range of 110–140 GHz are shown. The radar front end (RFE) is encapsulated using an epoxy molding compound, Polytec TC 430-T with suitable dielectric characteristics in the desired frequency range. The encapsulated RFE is surface mounted on a baseband printed circuit board, thereby realizing a fully functional 122-GHz frequency modulated continuous wave (FMCW) radar. The FMCW radar is used to measure the distance of a target, and the measurement results are compared with those of a commercial 122-GHz RFE.

The Effect of Processing Parameters on the Physical and Microwave Electrical Properties of Low Temperature Co-fired Ceramics

Low Temperature Co-fired Ceramics (LTCC) represent a multilayer electronic packaging technology with the ability to incorporate many electrical components such as conductive, resistive, and dielectric materials, into a single monolithic package. Example devices would include capacitors, inductors, resistors, antennae, transformers, hybrid circuits, etc. In general, the LTCC package consists of a glass/ceramic dielectric and compatible conductive inks (Au, Ag, etc.). The dielectrics and conductors are patterned/laminated to form the desired 3D structure and then co-fired to complete densification. The resulting monolithic block is mechanically robust with a high density of (often buried) electrical components. Typically, LTCC systems have found implementation in circuitry utilizing the RF and microwave frequency ranges. In general, the material design and processing parameters, and knowledge of how these affect the final mechanical and electrical properties of the LTCC package are needed for successful circuit design. The electronic performance of an LTCC dielectric/conductor system (Ferro L8) was investigated as a function of processing parameters (peak fire temperature, temperature ramp rate, furnace air flow, etc.). Comparisons were also made between multiple manufacturing sites as the mentioned processing parameters vary slightly from site to site even with nominally identical set points due to differences in furnace design, fab layout, etc. Material properties of fired parts such as effective permittivity and electrical losses were measured both on bare dielectric using resonant cavity methods and on the dielectric/conductor system as a whole using microstrip transmission line methods to frequencies as high as 50 GHz. Correlations were made between electrical performance and models based on material properties. The effects of varied processing parameters and processing sites were also studied and used to help establish process understanding and improvement with respect to high frequency electrical performance. As an example, optimization of electrical performance could be achieved by adjusting the nominal furnace temperature set point at a specific site where losses were slightly high even with identical processing parameters to those at another manufacturing site.

Low temperature co-fired ceramic packaging of CMOS capacitive sensor chip towards cell viability monitoring

Cell viability monitoring is an important part of biosafety evaluation for the detection of toxic effects on cells caused by nanomaterials, preferably by label-free, noninvasive, fast, and cost effective methods. These requirements can be met by monitoring cell viability with a capacitance-sensing integrated circuit (IC) microchip. The capacitance provides a measurement of the surface attachment of adherent cells as an indication of their health status. However, the moist, warm, and corrosive biological environment requires reliable packaging of the sensor chip. In this work, a second generation of low temperature co-fired ceramic (LTCC) technology was combined with flip-chip bonding to provide a durable package compatible with cell culture. The LTCC-packaged sensor chip was integrated with a printed circuit board, data acquisition device, and measurement-controlling software. The packaged sensor chip functioned well in the presence of cell medium and cells, with output voltages depending on the medium above the capacitors. Moreover, the manufacturing of microfluidic channels in the LTCC package was demonstrated.

Investigation of low-temperature cofired ceramics packages for high-temperature SAW sensors

Abstract. Surface acoustic wave (SAW) temperature sensor devices have been developed for operating temperatures up to and above 1000 °C. A challenging task to make these devices available on the market is to develop an appropriate housing concept. A concept based on low-temperature cofired ceramics (LTCC) has been investigated and tested under elevated temperatures up to 600 °C. The devices showed promising results up to 450 °C. Thorough analysis of the possible failure mechanisms was done to increase the maximum temperature above this limit in further production cycles.

Design and Analysis of LTCC-Integrated Planar Microstrip-to-Waveguide Transition at 300 GHz

A 300-GHz planar microstrip-to-waveguide transition in low-temperature co-fired ceramic (LTCC) is numerically and experimentally analyzed. A via fence and air holes are used to form a three-dimensional transition structure and a vertical hollow waveguide inside the multilayer LTCC substrate. The transition consists of a coplanar-waveguide-fed slot radiator backed by a short-wall of the waveguide and an open-circuited microstrip resonator. On the basis of the dual operation mechanism, the design guideline for the complex 3D structure is described using full wave analysis. The overall design is experimentally verified by a back-to-back transition which exhibits insertion loss of 4 dB at 300 GHz and 36-GHz bandwidth with better than 10-dB return loss. To evaluate the loss of a single transition, we carried out a loss component analysis by evaluating different lengths of microstrip line and hollow waveguide. The estimated loss for a single transition is 1 dB at 300 GHz. The planar transition without a metal back-short significantly reduces the size of terahertz packages and eliminates the need for additional components for hermetic sealing. The compact transition is easy to integrate in a low-cost LTCC package with an MMIC chip.

An Integrable SIW Phase Shifter in a Partially Magnetized Ferrite LTCC Package

There is a growing need for small size integrable phased antenna arrays for emerging satellite communications on-the-move applications. Traditional ferrite-based phase shifters are generally bulky due to the need of electromagnets for biasing, yielding them unsuitable for this kind of application. In this paper, a novel compact light-weight substrate integrated waveguide (SIW) based phase shifter realized in a multi-layer ferrite low-temperature co-fired ceramic package with embedded bias windings is reported. By using embedded windings and operating the material in a partially magnetized state, the required bias magnetic field could be significantly reduced from typically about 1000 Oe to less than 50 Oe. Moreover, the presented phase shifter has two modes of operations corresponding to two different biasing scenarios of the SIW, namely, symmetric and anti-symmetric bias. Under anti-symmetric bias, the phase shifter can achieve high nonreciprocal phase shift, whereas under symmetric bias, the phase shift is reciprocal, but the available phase shift is less than the anti-symmetric case. The fabricated prototype operates in the 11.5–13.5-GHz range and has a peak figure of merit (phase shift per decibel of loss) of 102 $^{\circ}/{\hbox{dB}} $ and a maximum phase shift per unit length of 153 $^{\circ} /{\hbox{cm}}$ , which are more than five times the previously reported figures for this technology. Due to the use of embedded windings, the presented phase shifter offers a huge size reduction from the order of ${\hbox{cm}}^{3}$ to ${\hbox{mm}}^{3}$ , making it particularly useful for mobile phased-array applications.

The Effect of Self-Heating on the Performance of a Tunable Filter With Embedded Windings in a Ferrite LTCC Package

Traditionally, ferrite-based tunable filters are biased by large and bulky electromagnets, which require high currents to overcome the dissipated fields at the air interface between the electromagnet and the ferrite substrate. This problem has been solved by implementing the windings inside the package using ferrite low-temperature co-fired ceramic (LTCC). However, these embedded windings, which are densely packed, generate heat that affects the characteristics of the ferrite material. In this paper, we investigated the heat effects due to embedded windings in ferrite LTCC filters. We also incorporated the heating effects into an electromagnetic simulation model and achieved a good agreement between the simulations and the measurements. We found that increasing the temperature of the filter module from 0 °C to 190 °C by external heating causes the center frequency of the filter to shift by about 1 GHz. Alternatively, when a dc current is passed through the bias windings, heat is generated in the windings to a temperature of 250 °C measured at 260 mA of current. This heat causes the tunability of the filter to increase by more than 2%.

Low Temperature Co-fired Ceramic Package for Lab-on-CMOS Applied in Cell Viability Monitoring

Lab-on-CMOS chips (LOCMOS) are sophisticated miniaturized analysis tools based on integrated circuit (IC) microchips performing various laboratory functions. We have developed a low temperature co-fired ceramic (LTCC) package for a LOCMOS application regarding cytotoxicity assessment of nanomaterials. The LTCC packaged capacitance sensor chip is designed for long-term cell viability monitoring during nanoparticle exposure. The introduced LTCC package utilizes the flip chip bonding technique, and it is biocompatible as well as able to withstand the environmental conditions required to maintain mammalian cell culture directly on the surface of a complementary metal oxide semiconductor (CMOS) integrated circuit.

Bandpass Filters With Localized Temperature Compensation Dielectrics in Low-Temperature Cofired Ceramic Packages

A series of SrTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (STO) based temperature compensation dielectrics that were cofireable with the commercial DuPont 951 low-temperature cofireable ceramic (LTCC) were developed. The STO30 dielectric with 30 wt% STO showed the highest positive temperature coefficient of resonant frequency (τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> ) that was opposite to the τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> = -69 ppm/°C of the Dupont 951 LTCC, and was selected to design a temperature-compensated four-pole bandpass filter. The filter shows a near zero τ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> = 0.7 ppm/°C over a temperature range -20 °C to 80 °C. The variance of insertion loss of the filter over the same temperature span is 0.28 dB. The maximum-difference group delay of the filter is 37 pS. The insertion loss included two SMA connectors at 20 °C is greater than 2.45 dB. A general variational method with the transmission-line technique provided an analytical method to calculate the effective dielectric constant and the characteristic impedance of an arbitrary multilayer strip line structure. With this method, the thickness of STO30 compensation dielectric can be optimized to obtain a nearly full temperature compensation for the filter. The electromagnetic simulation results of the filter agreed well with measured data.

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.

A study on the effect of wire bonding interconnects of BCB capped CPW to CPW on LTCC substrate

ABSTRACTThe effect of wire bonding interconnects between BCB capped CPW on silicon chip and CPW on low temperature cofired ceramic (LTCC) package is presented. The Si chip is attached onto LTCC package using conductive silver epoxy. Two different bond wires, ribbon‐wire and normal wire are used for the transition of CPW–CPW between Si chip and LTCC. The test module has been characterized up to 20 GHz. The CPW lines interconnected with normal wire has insertion loss of 0.6 dB at 5 GHz, while the ribbon wired ones show 0.5 dB at the same frequency. Lumped equivalent circuit model has been developed to figure out the behavior of the test module and three‐dimensional HFSS electromagnetic simulation has been also carried out. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1378–1381, 2014

An LTCC multilayer packaged 24‐Ghz short‐range radar with an embeded Tx leakage canceller

AbstractThe high isolation performance of a Tx leakage canceller was demonstrated using low temperature cofired ceramics (LTCC) technology. The Tx‐to‐Rx isolation of −52 dB was achieved at 24.15 GHz. The parasitic effects of the Tx leakage canceller were studied for the purpose of reducing Tx leakage. A method involving the vertical stacking of a three‐dimensional LTCC packaging module and an FR‐4 substrate was developed, and a compact 24‐GHz quadrature Doppler radar front‐end module was fabricated. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:671–677, 2014

High Pressure Sensor with PZT Transducer in LTCC Package

Abstract Design, technology and properties of a completely ceramic piezoelectric pressure sensor are described. The sensor is made of the LTCC (Low Temperature Co-fired Ceramics) with PZT (Lead Zirconate Titanate) transducer and is designed to withstand pressure up to 10 MPa. The device is a sensor and a package simultaneously. It can be directly screw mounted to a flat surface with a hole supplying a pressure. Two methods of detection are considered: shift of the resonant frequency for static loads detection and charge response for dynamically changing load. Measurements are carried out for maximum 6 MPa pressure. The sensor exhibits linear charge response and resonant frequency shift in tested range.

고전력 LED용 적층형 LTCC 패키징의 ZnO 조성 변화가 방열 특성에 미치는 영향

신뢰성이 우수하며, 소형화가 가능하고, 우수한 열전도도의 은 전극을 이용할 수 있는 LTCC (Low temperature co-fired ceramic) 패키징은 환경 및 열에 약한 플라스틱 패키징을 대체할 것으로 기대받고 있다. 현재 LTCC 패키징의 원료 분말로는 주로 <TEX>$Al_2O_3$</TEX>을 사용하는데, 본 연구에서는 <TEX>$Al_2O_3$</TEX>보다 열전도도가 2배 우수한 ZnO을 일부 첨가 또는 대체한 조성 변화를 통하여 패키징의 열 특성 변화에 대해 연구하였다. 소량의 ZnO를 첨가하여 열전도도가 최대 25%까지 상승하는 결과가 나타났으며, 이 결과로 LED 수명이 증가할 것으로 예상된다. ANSYS 시뮬레이션 결과 열 유속의 값이 ZnO가 첨가된 경우 최대 56% 증가함을 확인할 수 있었다. 실제 LED 패키징을 제작하여 측정한 결과도 ZnO를 첨가한 LTCC 패키징은 <TEX>$Al_2O_3$</TEX>로만 이루어진 패키징보다 열저항이 최대 14.9% 감소하였다. LTCC (Low temperature co-fired ceramic) package have been paid much attention due its good reliability, miniaturization, and application of silver paste with complex wiring and printing. Therefore, LTCC package has been expected to replace vulnerable plastic package in the field of high power LED device. Currently, LTCC ceramic package is mainly made up of aluminum oxide powder. In this study, zinc oxide powder is added or replaced for the fabrication of LTCC ceramic body. By adding small amount of ZnO, thermal conductivity of the LTCC ceramic body could be remarkably increased by 25% leading to the extension of LED life time. The LTCC package structure with composition including ZnO has an increased thermal flux by 56% as a result of ANSYS simulation. Actually, the fabricated LED package with the addition of ZnO exhibits a decreased thermal resistivity by 14.9%.

Gas Permeation Measurements on Low Temperature Cofired Ceramics

Commercial low temperature cofired ceramic (LTCC) technology is established in microelectronics and microsystems packaging, multichip and radio frequency (RF) modules, and sensors. The ability to combine structural considerations with embedded traces and components using laminated glass-ceramic tapes has created solutions to unconventional packaging requirements of micro-electro-mechanical systems (MEMS) devices. Many MEMS devices such as resonators are very sensitive to pressure and require packaging in a vacuum environment. Attaining and maintaining desirable pressure levels in sealed vacuum packages requires knowledge of the permeation characteristics of the vacuum envelope and the sealing materials. An experimental system to measure the time dependent gas permeation through LTCC at temperatures from room temperature to 500°C has been developed. This system utilizes a membrane technique in which a gas is allowed to permeate through a test sample, held at a constant temperature, into a high vacuum chamber where it is detected using mass spectrometry. The gas permeation value is determined from the steady state gas flux through the sample. The gas diffusivity and solubility in the material were calculated using data from the time dependent approach to the steady state condition. The gas-solid permeation data for helium through DuPont 951 LTCC is presented and compared to the permeation through other common vacuum envelope materials such as glasses and high-purity alumina ceramics. Application of the permeation data to the prediction of vacuum levels inside typical LTCC packaging is discussed. This data can further be utilized in designs to create LTCC packages that meet specific pressure/time operating requirements.

Lifetime enhancement of high-power light-emitting diodes using thermal paths in ceramic package

By inserting the Ag thermal paths located under the GaN-based light-emitting diode (LED) chip in a low-temperature co-fired ceramic package, junction-to-atmosphere thermal resistance could be reduced from 53 to 13 K/W. Temperature-stress accelerated life tests were carried out to check the effect of thermal improvement on reliability and to estimate lifetime as a function of junction temperature. After a 4000-hour test, the lifetimes of the degraded LED packages were estimated. The mean time to failure (MTTF) was below 20 000 hours at 35°C atmosphere temperature for the conventional LEDs. On the other hand, the estimated MTTF was over 50 000 at the same atmosphere temperature for the improved LEDs.

Integrated LTCC packaging for use in biomedical devices

As implantable devices gain more widespread use, medical device manufacturers are constantly looking for novel materials that increase and improve capability and functionality. The packaging needs to be biocompatible, but it is also highly desirable for it to be radio transparent to facilitate wireless telemetry and remote powering. Low temperature co-fired ceramics (LTCC) provide a viable solution that meets these desired specifications while also having characteristics that support ease of manufacturing such as the ability for molding, shaping, and even embedding components within the material. In this work, inductor coils used for wireless telemetry and powering are integrated into the walls of the LTCC-based package to maximize the size of the passive component while optimizing the miniaturization of the implant. The package designed and fabricated in this work consisted of inductors approximating 20 mH with a quality factor of 7.8 at 2 MHz. When compared to similar devices in the literature the LTCC inductor out performed these devices when a power-link figure of merit is used for comparison.