新型封装材料与大功率LED封装热管理

高效散热封装材料的合理选择和有效使用是提高大功率LED(发光二极管)封装可靠性的重要环节。在分析封装系统热阻对LED性能的影响及对传统散热封装材料性能进行比较的基础上,阐述了金属芯印刷电路板材料、金属基绝缘板材料、陶瓷基板材料、导热界面材料和金属基复合材料结构特点、导热性能及其封装应用实例。指出了封装材料的研究重点和亟待解决的问题。     

Characterization of chip scale packaging materials

The mechanical stability of Chip Scale Packages (CSP) used in surface mount technology is of primary concern. The dominant issues are package warpage and solder fatigue in solder joints under cyclic loads. To address these issues, molding compound and die attach film were characterized with finite element method which employed a viscoelastic and viscoplastic constitutive model. The model was verified with experiments on package warpage, PCB warpage and solder joint reliability. After the correlation was observed, the effect of molding compound and die attach film on package warpage and solder joint reliability was investigated. It was found that package warpage tremendously affected solder joint reliability. Furthermore, a die attach film was developed based on results of the modeling. CSP with the developed die attach film are robust and capable of withstanding the thermal stresses, humidity and high temperatures encountered in typical package assembly and die attach processes. Also, a lead free solder is discussed based on the results of creep testing. This paper presents the viscoelastic and viscoplastic constitutive model and its verification, the optimum material properties, the experimental and simulated reliability and performance results of the u*BGA packages, and the lead free solder creep.     

The impact of plasma-charging damage on the RF performance ofdeep-submicron MOSFET

Integration of RF analog functions with CMOS digital circuits offers great advantages in terms of cost and performance. Plasma-charging damage is known to degrade MOSFET characteristics and can be expected to impact the RF performance as well. In this work, we present for the first time a thorough investigation of the impact of plasma-charging damage on the RF characteristics of deep-submicron MOSFET. Our result shows that, with ultra-thin gate oxide, a 400°C forming gas annealing can completely recover the RF performance degradation due to plasma-charging damage     

Insights into the influence of fluorination positions on polymer donor materials on photovoltaic performance

To explore the influence of fluoro substitution position and number on optical, electrochemical and photovoltaic properties, three novel donor-acceptor (D-A) alternative copolymers (PHF, PFH and PFF) were synthesized by Stille polycondensation of 2,3-diphenyl-5,8-di(thiophen-2-yl)quinoxaline (DTQx) acceptor unit and indacenodithiophene (IDT) donor unit. As films, PHF and PFF comprising two fluoro substituents on the lateral phenyl groups displayed a broad absorption ranging from 350 to 700 nm; whereas PFH containing two fluorine atoms on the polymer main chain exhibited a slightly narrower absorption ranging from 350 to 650 nm. In addition, fluoro substitution on the polymer main chain can lower the HOMO level of the resulted polymers. As expected, PFH and PFF possess deeper HOMO energy level than PHF. Polymer solar cells (PSCs) were fabricated with these three polymers as donor materials and PC₇₁BM as acceptor material. PHF based PSCs gave a power conversion efficiency (PCE) of 7.2% with a V_oc of 0.84 V, a J_sc of 12.46 mA/cm² and an FF of 0.69. And PFH based PSCs showed a PCE of 6.19% with a V_oc of 0.93 V, a J_sc of 9.57 mA/cm² and an FF 0.70. However, a PCE of only 2.9% with a V_oc of 0.92 V, a J_sc of 4.61 mA/cm² and an FF of 0.68 was obtained for PFF based PSCs. Transmission electron microscopy (TEM) and resonant soft X-ray scattering (R-SoXS) studies indicated that the introduction of four fluorine atoms at each repeating unit can spoil the morphology of active layer. These results highlight the importance of fluorination position and number to the performance of PSCs.     

RF performance of diamond MISFETs

A cutoff frequency (f_T) of 11 GHz is realized in the hydrogen-terminated surface channel diamond metal-insulator-semiconductor field-effect transistor (MISFET) with 0.7 μm gate length. This value is five times higher than that of 2 μm gate metal-semiconductor (MES) FETs and the maximum value in diamond FETs at present. Utilizing CaF₂ as an insulator in the MIS structure, the gate-source capacitance is reduced to half that of the diamond MESFET because of the gate insulator capacitance being in series to the surface-channel capacitance. This FET also exhibits the highest f _max of 18 GHz and 15 dB of power gain at 2 GHz. The high-frequency equivalent circuits of diamond MISFET are deduced from the S-parameters obtained from RF measurement     

Analysis of RF MEMS switch packaging Process for yield improvement

Radio frequency microelectro-mechanical systems (RF MEMS) switches offer significant performance advantages in high-frequency RF applications. The switches are actuated by electrostatic force when voltage was applied to the electrodes. Such devices provide high isolation when open and low contact resistance when closed. However, during the packaging process, there are various possible failure modes that may affect the switch yield and performance. The RF MEMS switches were first placed in a package and went through lid seal at 320degC. The assembled packages were then attached to a printed circuit board at 220degC. During the process, some switches failed due to electrical shorting. Interestingly, more failures were observed at the lower temperature of 220degC rather than 320degC. The failure mode was associated with the shorting bar and the cantilever design. Finite element simulations and simplified analytical solutions were used to understand the mechanics driving the behaviors. Simulation results have shown excellent agreement with experimental observations and measurements. Various solutions in package configurations were explored to overcome the hurdles in MEMS packaging and achieve better yield and performance     

Noise generation,propagation and effects on RF components in system-on-a-chip packaging

Substrate coupling noise effects in wireless receiver systems in terms of the crosstalk power spectral density induced from the fast switching digital circuits is the center of study in this paper. Deterioration in performance of a low noise amplifier is plotted against various values of die-attach inductance, inductance on digital ground pins, physical separation between the analog and digital circuits on-chip, number of simultaneous switching output buffers, etc. Different Ball Grid Array Packages, both the wire bonded and flip-chip attached versions have been studied. The return loss and insertion loss for paths from the on-chip wire bond pad to connect pads on the printed circuit boards have been plotted. Results show that noise reduces by a greater amount for reduction in die-attach inductance as compared to a reduction in inductance on the digital ground pin.     

RF power performance of an LDMOSFET on high-resistivity SOI

This paper describes the RF power performance of an LDMOSFET technology on high-resistivity silicon-on-insulator wafers. The technology has an on-state breakdown voltage of greater than 10 V, and an off-state breakdown voltage of greater than 20 V. This device technology is shown to have excellent RF power characteristics at frequencies from 1.9 to 5.8 GHz. At 1.9 GHz, a peak power-added efficiency (PAE) of 63% was achieved with an output power of up to 520 mW from a single RF power cell. At 5.8 GHz, a peak PAE of 35% was achieved with an output power of up to 125 mW from a single RF power cell.     

RF performance of SiC MESFET's on high resistivity substrates

State-of-the art SiC MESFET's showing a record high f_max of 26 GHz and RF gain of 8.5 dB at 10 GHz are described in this paper. These results were obtained by using high-resistivity SiC substrates for the first time to minimize substrate parasitics. The fabrication and characterization of these devices are discussed     

Nano materials for microelectronic and photonic packaging

This paper addresses the state-of-the-art nano-science and technology regarding next generation high density microelectronics and photonics packaging applica-tions, including carbon nanotubes (CNTs) for electrical/thermal devices, and molecular wires for electrical interconnects, etc.     

Permittivity and permeability measurement of microwave packaging materials

There has recently been a growing interest in using new packaging materials-dielectric and/or magnetic-in a wide variety of applications for controlling the microwave heating of food. The study of the thermal behavior of these products requires the accurate determination of the complex permittivity and permeability when the temperature varies, and when the materials are irradiated in specific conditions. One of the main challenges is to distinguish the dielectric losses from the magnetic ones. In this paper, a practical measurement method is proposed, which consists of irradiating a rod sample successively with a homogeneous electric-field distribution with a low magnetic field and with a homogeneous magnetic-field distribution with low electric field. An accurate and efficient electromagnetic analysis tool is used to generate a set of points, which allow the construction of several bilinear functions that relate the scattering parameters of the circuit to the complex values of /spl epsiv/ and /spl mu/ so that /spl epsiv/ and /spl mu/ can then be easily determined from experimental measurements in accordance to whatever the special irradiation conditions. Some results for test materials are presented and discussed.     

组播路由协议对网络性能的影响

组播技术对Internet发展至关重要，它以高效、可扩展的方式发送单点到多点、多点到多点数据，很多专家认为它必然成为下一代互联网的关键技术之一。现就其中组播路由协议对网络性能的影响进行了研究。     

The influence of eddy currents on magnetic actuator performance

In this letter the effects of eddy currents on the transient performance of electromagnetic actuators is discussed. It is shown that a transfer function representation, that includes a first-order model of the eddy current influence, can be obtained which is suitable for control system analysis.     

Fabrication and performance of novel RF spiral inductors on silicon

This paper presents and discusses the fabrication and the performance of RF circular spiral inductors on silicon. The substrate materials underneath the inductor coil are removed by wet etching process. In the fabrication process, fine polishing of the photoresist is used to simplify the processes and ensure the seed layer and the pillars contact perfectly, and dry etching technique is used to remove the seed layer. The results show that Q-factor of the novel inductor is greatly improved by removing the silicon underneath the inductor coil. The spiral inductor for line width of 50 μm has a peak Q-factor of 17 at frequency of 1 GHz. The inductance is about 3.2 nH in the frequency range of 0.05-3 GHz and the resonance frequency of the inductors is about 6 GHz. If the strip is widened to 80 μm, the peak Q-factor of the inductor reduces to about 10 and the inductance is 1.5 nH in the same frequency range.     

The influence of hydrogen gas on the characteristics of amorphous silicon deposited by RF sputtering

The electrical and optical properties of a-Si depend greatly on the fill gas and substrate temperature during RF sputtering. From the measured absorption coefficient, it was estimated that after the introduction of H₂ gas during sputtering the gap state density reduces from 3.2 × 10¹⁹ cm^?3 to 4.8 × 10¹⁷ cm^?3. As a consequence the optical band gap was found to increase from 1.74 to 1.82 eV. The d.c. conductivity measurement shows three distinct conducting mechanisms at different temperature regions. The SiH bonds in RF sputtered samples are persistant to higher temperature treatment than the CVD prepared ones.     

Multichip packaging and the need for new materials

The sole determiner of speed, of cost, and of possible system size is the interconnection density of the circuits. The best way to increase the interconnection density is to reduce the dielectric constant, and there are new materials that offer almost a 2:1 reduction. Designing new modules with these low dielectric constant materials and with larger chips increases the wattage and increases the wattage density. Ceramic substrates must be used to dissipate the heat of the new large higher wattage chips without destroying them. This requires the use of new ceramic materials. A choice must be made between the leading contenders. A new multichip module technology is being defined, and will result in a major packaging change. The processes and the materials choices are presently overwhelming, but there are great advantages to those who identify the best solutions.     

Polyimidesiloxanes: Emerging materials for advanced packaging applications

A brief history for development of polyimidesiloxanes is provided. Many useful properties of SIM materials, such as processing conditions, adhesion properties, water absorption, Tg’s, electrical and thermal properties, and Young’s Modulus are revealed. The SIM materials discussed in the present article, are state of the polyimidesiloxanes, which represent the best combinations of advantageous properties for high density packaging applications: They have the best combinations of high Tg’s, thermal stability with low water absorption, moduli and dielectric constants.     

电子缓存器容量对QUADRO-Star性能的影响

QUADRO-Star是一种带有光缓存器的波分复用超高速局域网结构,这种网络在发射机中应用电子缓存器,在接收机中应用光缓存器.电子缓存器和光缓存器对网络性能的影响是不同的.通过网络模拟的方法,得出了电子缓存器容量的变化对吞吐量、延迟、数据包的发射次数和丢包率的影响.