Investigation on a new silver photoimageable conductor

A new thick film photoimageable silver paste of improved properties has been elaborated. The paste is less sensitive to the visible light. Certain disadvantages of most commercially available materials, such as necessity of operating with the paste in the room illuminating with yellow, green or red light has been eliminated. Further improvement of conductive silver pastes to enable reducing lines width down to 10 μm has been done.     

New conductive thick-film paste based on silver nanopowder for high power and high temperature applications

A new thick-film material for screen-printing technology, based on nanoscale silver powders with the particle size distribution 5-55 nm is presented. Silver nanopowder used for paste preparation was elaborated by the authors. The compatibility of investigated paste was proven with alumina, silicon, Kapton foil and glass. The main advantage of this paste is sinterability at much lower temperatures (around 300 °C) compared to pastes obtained from micro-powders (650-850 °C). The thicknesses of obtained layers are 2-3 μm. The elaborated layers are dense and well sintered, exhibit good adhesion to all above mentioned substrates and low resistivity as well as very good resistance to high power and elevated temperatures. The results of loading the layers deposited on alumina substrates with high current and exposed to high temperature are presented as well.     

Temperature Distribution of a Low Temperature Heat Pipe with Multiple Heaters for Electronic Cooling

A numerical study has been performed to predict the characteristics on the transient operation of the heat pipe with multiple heaters for electronic cooling. The model of the heat pipe was composed of the evaporator section with four heaters, insulated transport section, and the condensor section with a conductor which is cooled with uniform heat flux condition to surrounding. The governing equations and the boundary conditions were solved by the generalized PHOENICS computational code employing the finite volume method. Two test cases are investigated in present study; Case 1 indicates that the 1st and 2nd heaters among four heating sources are heated off, while the 3rd and 4th heaters are heated on. Case 2 is the inverse situation switched from heating location of Case 1. The results show that the transient time to reach the steady state is shorter for Case 1 than for Case 2. Especially, the temperature difference of the heater during switching operation is relatively small compared to the maximum all- owable operating temperature difference in electronic system. Hence, it is predicted that the heat pipe in present study operates with thermally good reliability even for switching the heaters.     

Microcapacitors with controlled electrical capacity in the pF–nF range printed by laser-induced forward transfer (LIFT)

Micrometric-sized pixels of hybrid organic–inorganic thin films (Ag/parylene-C) have been printed by laser-induced forward transfer (LIFT) on flexible, cost-efficient substrates. Micrometric capacitors have been fabricated by laser printing such pixels together with silver nanoparticles (AgNP) paste. The AgNP paste has been deposited in the shape of square pads, acting as bottom electrode. This combination is suitable to be used in microelectronic circuits, as the electrical components exhibit controllable capacity in the pF–nF range. Electrical characterizations of the printed pixels demonstrate that the capacitors are fully operative and stable over time.     

Localized bonding processes for assembly and packaging of polymeric MEMS

Localized bonding schemes for the assembly and packaging of polymer-based microelectromechanical systems (MEMS) devices have been successfully demonstrated. These include three bonding systems of plastics-to-silicon, plastics-to-glass, and plastics-to-plastics combinations based on two bonding processes of localized resistive heating: 1) built-in resistive heaters and 2) reusable resistive heaters. In the prototype demonstrations, aluminum thin films are deposited and patterned as resistive heaters and plastic materials are locally melted and solidified for bonding. A typical contact pressure of 0.4 MPa is applied to assure intimate contact of the two bonding substrates and the localized bonding process is completed within less than 0.25 s of heating. It is estimated that the local temperature at the bonding interface can reach above 150/spl deg/C while the substrate temperature away from the heaters can be controlled to be under 40/spl deg/C during the bonding process. The approach of localized heating for bonding of plastic materials while maintaining low temperature globally enables direct sealing of polymer-based MEMS without dispensing additional adhesives or damaging preexisting, temperature-sensitive substances. Furthermore, water encapsulation by plastics-to-plastics bonding is successfully performed to demonstrate the capability of low temperature processing. As such, this technique can be applied broadly in plastic assembly, packaging, and liquid encapsulation for microsystems, including microfluidic devices.     

Design and fabrication of thin film resistive heaters for hybrid optoelectronic packaging

This paper presents the technology for the design and fabrication of planar resistive heaters made from vacuum deposited nichrome thin films on a quartz substrate. These heaters are suitable as isolated local heat sources for melting solder to attach discrete components on a hybrid optoelectronic integration platform. Numerical simulations are performed using the Finite Element Method (FEM) to determine the geometry of the heaters in order to deliver adequate thermal performance. Multiple heater elements are batch processed on a 3.0 in polished fused quartz wafer using standard photolithographic techniques. Use of polyimide as a reliable insulation layer between the nichrome thin film and the solder has improved the thermal uniformity over the heater surface. Individual heaters can reach temperatures close to 300/spl deg/C drawing 7.1 W of power on an uncooled alumina platform and 12.0 W on an uncooled copper platform. This temperature is high enough to melt gold-tin (AuSn) solder (with eutectic melting point of 280/spl deg/C), typically used for attaching different optoelectronic components on a substrate.     

适合铝丝键合后热老化要求的金导体浆料

研究了一种适合铝丝键合后热老化要求的金导体浆料，性能达到使用要求。在金浆中添加了少量合金元素，并选用混合型粘结剂。对金导体铝丝焊后热老化失效机理以及添加合金元素的作用，进行了讨论     

Multilayer resonators and a bandpass filter fabricated from a novel low-temperature co-fired ceramic

The main objective of this study was to make components from a novel low-loss, low-temperature Co-fired ceramic (LTCC) dielectric, which was also compatible with a high-conductivity silver paste. The multilayer-component fabrication procedure is presented together with a composition for a tape-casting slurry, choice of conductor paste, and LTCC process parameters. A good Q factor, >100 at 2 GHz, using the novel material system has been achieved for λ/2 resonators operating in the frequency range 1.7–3.7 GHz. An excellent frequency response for a 2 GHz bandpass filter has also been achieved; the insertion losses in the passband were less than −2 dB (bandwidth 60 MHz) and the attenuation more than 25 dB in the stopband located 190 MHz higher.     

一种基于CMOS工艺的二维风速传感器的设计和测试

给出了一种完全基于CM O S工艺的、能同时测量风速和风向的二维测风传感器的结构、工作原理及其测试结果。该传感器采用恒温差工作模式,热堆输出电压平均值反映芯片温度和环境温度的差,省去了测温二极管。风速测量采用热损失型原理,因此不存在速度量程问题;同时通过四周对称分布热堆的相对差分输出得到风向,风向的测试和风速无关。测试电路是由普通运放电路组成的控制和测试系统。经过风洞测试,风速的测量可以达到23m/s,风速分辨率达到0.5 m/s,风速的最大误差为0.5 m/s。传感器的反应时间为3~5秒,整个功率损耗约为500 mW。     

焊膏可印刷性评价方法的研究

焊膏的印刷性能是SMT中最致SMA的各种缺陷.介绍一种焊膏的印刷性能测试方法,其特点是采用了"刀-环"印刷结构,其中模板设计成环形来实现连续的印刷.此外在环形模板内焊膏滚动的切线方向上安装J形探针,监测焊膏的滚动印刷阻力.通过对几种焊膏的滚动印刷试验,并对可印刷性能进行了评价分析,力求获得一个简单的评价焊膏可印刷性能的指标.焊膏印刷阻力呈下降趋势,在滚动停止时跌倒到最小值.以最终的印刷距离作为焊膏的印刷寿命或者耐受值,由此来有效评估焊膏可印刷性.     

Effect of Colloidal Silver on Optical Transmittance Characteristics of Bulk Cadmium Zinc Telluride Crystals

Colloidal silver is observed to affect the transmittance of p-type Cd_1−y Zn _y Te (CZT) single-crystal substrate material at room temperature. The optical transmittance spectra have been analyzed in the near-infrared (NIR) and mid-infrared (MIR) regions. The transmittance characteristics of CZT showed significant reduction in absorption due to split-off valance band transitions in the NIR region and intervalence band absorption in the MIR region upon coating CZT substrates with silver paste. This reduction in absorption has been explained to be due to the compensation of the acceptor defects (native and foreign). Silver atoms incorporated from the silver coating help in compensation of these defects. A similar effect on transmittance characteristics of mercury cadmium telluride (MCT) epilayers grown on CZT substrates after coating silver paste on the CZT substrate side was also observed. An improvement in the transmittance of CZT substrates after the application of silver paste was observed. A similar improvement in transmittance is usually achieved by annealing the substrates in a Cd/Zn atmosphere. The results are explained by considering the formation of neutral complexes of acceptors (cadmium vacancies) and the interstitial silver. This study also points to the important conclusion that silver paste on CZT should be applied with caution for measurement purposes since it diffuses even at room temperature and modifies the optical characteristics.     

Direct gravure printing (DGP) method for printing fine-line electrical circuits on ceramics

The tendency toward higher packing densities and higher frequencies for telecommunication devices based on ceramic technology requires smaller dimensions for electrical wiring. Electrical thick-film circuits for ceramic and LTCC-substrates have, up to now, been printed with screen printing, where the printing lines width limit is about 125 /spl mu/m in mass production. A silicone polymer direct gravure printing (Si-DGP) process has been developed to perform smaller dimensions, down to 20 /spl mu/m lines width, for electrical circuitry. In the DGP process, the conductor paste is doctored to the grooves of the gravure and then it is pressed against the substrate. The paste is, thus, printed directly onto the substrate from the patterned gravure. The results showed that, using the DGP process, it was possible to print conductor lines down to 20 /spl mu/m in width. It was also noted that a 100% transfer of paste from the grooves of the gravure could be obtained with commercial pastes using the silicone polymer gravure. A dried thickness of up to 28 /spl mu/m was measured for the narrowest lines. Also conductor lines printed by the Si-DGP method were embedded inside LTCC-module.     

薄膜开关用导电碳浆的研究

研究了薄膜开关用导电碳浆的基本配方和工艺过程;实验表明:胶粘剂树脂柔韧性的选择至关重要,以满足柔性线路的基本要求;导电载体应使用质量比为6:4的石墨和炭黑的混合体,适当的分散剂可使电阻率降低1/2,碳浆研磨次数为4次;采用本研究方法制出涂料的成膜方阻为12 ?□。     

玻璃釉包覆片式NTC热敏电阻器的研制

为了得到更稳定、可靠的片式NTC热敏电阻器,在芯片表面涂覆一层玻璃釉是有效的途径之一。为此调整了玻璃釉包覆片式NTC热敏电阻器所进行的工艺,进行了玻璃浆及银浆的选取和匹配工作。所研制的片式NTC热敏电阻器,克服了传统片式NTC热敏电阻的精度不高、稳定性不好、可靠性差等主要缺点,F级阻值合格率提高了45%,阻值的年漂移小于0.1%,端电极强度提高了约4.9N,耐焊上锡率提高了约5%。     

银/导电陶瓷复合电极浆料导电性的研究

采用银和导电陶瓷(LaNiO3和LaFe0.25Ni0.75O3)作复合电极浆料,并研究了复合电极浆料的导电性与导电陶瓷比例及种类的关系。结果发现,复合电极浆料的电阻率随导电陶瓷比例的增加而增大,当LaNiO3和LaFe0.25Ni0.75O3两种导电陶瓷的质量分数<15%时,两种复合浆料的导电性均变化不大。SEM观测显示,复合电极浆料制成的电极有很好的烧成表面。     

Thermal management of BioMEMS: temperature control for ceramic-based PCR and DNA detection devices

Integrated microfluidic devices for amplification and detection of biological samples that employ closed-loop temperature monitoring and control have been demonstrated within a multilayer low temperature co-fired ceramics (LTCC) platform. Devices designed within this platform demonstrate a high level of integration including integrated microfluidic channels, thick-film screen-printed Ag-Pd heaters, surface mounted temperature sensors, and air-gaps for thermal isolation. In addition, thermal-fluidic finite element models have been developed using CFDRC ACE+ software which allows for optimization of such parameters as heater input power, fluid flow rate, sensor placement, and air-gap size and placement. Two examples of devices that make use of these concepts are provided. The first is a continuous flow polymerase chain reaction (PCR) device that requires three thermally isolated zones of 94/spl deg/C, 65/spl deg/C, and 72/spl deg/C, and the second is an electronic DNA detection chip which requires hybridization at 35/spl deg/C. Both devices contain integrated heaters and surface mount silicon transistors which function as temperature sensors. Closed loop feedback control is provided by an external PI controller that monitors the temperature dependant I-V relationship of the sensor and adjusts heater power accordingly. Experimental data confirms that better than /spl plusmn/0.5/spl deg/C can be maintained for these devices irrespective of changing ambient conditions. In addition, good matching with model predictions has been achieved, thus providing a powerful design tool for thermal-fluidic microsystems.     

Technical challenges of stencil printing technology for ultra fine pitch flip chip bumping

Stencil printing remains the technology route of choice for flip chip bumping because of its economical advantages over traditionally costly evaporation and electroplating processes. This paper provides the first research results on stencil printing of 80 and 60 μm pitch peripheral array configurations with Type 7 Sn63/Pb37 solder paste. In specific, the paste particle size ranges from 2 to 11μm with an average particle size of 6.5 μm taken into account for aperture packing considerations. Furthermore, the present study unveils the determining role of stencil design and paste characteristics on the final bumping results. The limitations of stencil design are discussed and guidelines for printing improvement are given. Printing of Type 7 solder paste has yielded promising results. Solder bump deposits of 25 and 42 μm have been demonstrated on 80 μm pitch rectangular and round pads, respectively. Stencil printing challenges at 60 μm pitch peripheral arrays are also discussed.     

表面贴装技术手工操作工艺

依据表面贴装技术(SMT)工业生产流程、SMT设备原理、表面贴装工程品质要求,提出了简便易行的表面贴装技术手工操作工艺方案,用SMT焊接技术来分析其工艺流程及工艺参数.介绍了表面贴装技术的工艺原理、工艺过程、手工操作方法及其特点,提供了表面贴装技术手工操作设备的配置、设计制作及使用方法,对印刷焊膏、表面贴装器件(SMD)贴装、回流焊接温度控制等关键工序提出了相应的品质要求和注意点,并对常见的焊接缺陷作了简单分析,解决了印制焊膏、贴装元器件、焊接、清洗、检测、返修等SMT焊接技术.     

Polymer film deposition with fine pitch openings by stencil printing

It is confirmed that stencil printing with a novel developed printable polyimide paste can be used for polymer film deposition on LSI wafers. A thick polyimide film with openings for solder ball bumping can be deposited on all of the LSIs on a wafer by stencil printing at one time. This stencil printing process does not need an expensive lithography process, providing cost-effective wafer-level chip scale packages (WLCSPs). In this study, a novel polyimide paste was tailored to have a higher thixotropy ratio than conventional printable polyimide materials. The novel printable polyimide paste shows that the viscosity ratio of more than 3.5 at the shear rate of 1 to 10 s⁻¹ and that the viscosity increases rapidly after the shear rate is lowered. Fine spaces of 40 μm between 250 μm openings were obtained for 10 μm thick polyimide films on Si wafers. It has been also confirmed that the new paste shows the variation range of 30 μm at the opening size of 385 μm within 100 continuously printed wafers. Even after the new paste was shear-thinned repeatedly, rheological behavior of the new paste was not changed. This robustness leads to higher efficiency of the materials for mass-producing. From the reliability viewpoint of the printed polyimide films, no peelings were observed on plasma-CVD SiN films after the pressure cooker test under the condition of 127 °C and 0.25 MPa with the humidity of 100% for 300 h. The optimal stencil printing process using the novel developed paste will lead to significant cost reduction of a patterned polymer deposition process. Finally, WLCSPs using the stencil printing of the new polyimide paste have been demonstrated for SRAM LSIs on 8-in. wafers.     

SAC105焊锡膏的开发与评价

采用低银化焊料合金是无铅化电子组装提高性价比的发展趋势。开发了采用SAC105低银焊料合金的SUPER105系列焊锡膏,抗氧化、表面绝缘电阻、印刷性能、BGA空洞率、焊点推力等测试结果表明,SUPER105焊锡膏完全适用于消费类电子产品组装。