用硅压阻应力传感器研究倒装芯片封装应力

电子封装是集成电路产品制造过程中的重要环节,而电子封装所产生的应力则可能会对芯片的性能及可靠性产生影响,因而受到业界的广泛关注。利用半导体压阻效应制造硅压阻应力传感器阵列芯片,将其倒装键合至印刷电路板,填充不同类型的下填料进行固化。通过测量应力传感器芯片上的力敏电阻变化,计算倒装键合和下填料固化等封装工艺引入的应力,并讨论了下填料的性能参数对芯片应力大小的影响。此外,在标定力敏电阻及压阻系数温度效应的基础上,对下填料固化过程的应力变化进行了实时监测,分析了下填料固化工艺引起的应力。     

多晶硅隧道压阻模型*

基于陷阱模型,分析了多晶硅能带结构和导电机理,给出了解释隧道压阻效应的等效电路,说明了构成多晶硅压阻效应的内在因素以及隧道压阻效应在其中的作用。综合晶界区域和晶粒中性区两方面压阻效应建立了新的压阻模型——隧道压阻模型。结果表明,掺杂浓度在1020cm-3以上,复合晶界的压阻系数不但大于晶粒中性区的压阻系数,而且随掺杂浓度增加而增大,从而揭示了多晶硅纳米薄膜在重掺杂情况下出现应变因子随掺杂浓增加而增大的重要实验现象的内在机理。     

紫外光固化电磁屏蔽涂料的特性研究

以镀银铜粉为导电填料,以聚氨酯丙烯酸酯UV光固化树脂为基体材料,研制了UV光固化电磁屏蔽导电涂料。测试结果表明:该涂料的导电性能不但与填料含量、引发剂种类和含量有关,而且随涂层厚度的增强其电磁屏蔽效能增大。     

碳黑用量对硅橡胶压阻材料性能的影响

以高导电纳米碳黑为导电填料,甲基乙烯基硅橡胶为基材,制备出了硅橡胶压阻材料,并对其电性能和力学性能进行了表征。研究了碳黑用量对硅橡胶压阻材料电性能、压缩应力松弛性能以及电阻蠕变性能的影响。结果表明,碳黑用量对硅橡胶压阻材料的性能影响很大。当碳黑用量为质量分数14%~16%时,所制得的硅橡胶压阻材料性能优良,在反复加载20次的过程中,其压阻曲线的重复性很好,这为其下一步的器件化提供了可能。     

P型硅纳米板压阻特性的理论研究

考虑量子尺寸效应与自旋轨道耦合作用,从含有应变的6×6 Luttinger-Kohn哈密顿量出发,采用有限差分方法建立了p型硅纳米板的能带结构模型.基于硅纳米板压阻特性与其能带结构的相关性,采用改进的压阻理论定量分析了厚度、杂质浓度与温度对其压阻系数的影响.研究结果表明:量子尺寸效应强烈改变了硅纳米板的能带结构,是其压阻系数增大的主要因素,而自旋轨道耦合作用仅对含较高应变的硅纳米板的能带结构有较大影响;硅纳米板的压阻系数具有尺寸效应,随厚度减小而增大,随杂质浓度增加或温度升高而减小.在高简并条件下,硅纳米板的压阻系数与温度无关,完全由杂质浓度的大小控制;在非简并条件下,情况刚好相反.最后,利用施加应力前后空穴等能面形状的变化定性分析了硅纳米板压阻特性的起源.     

P型硅纳米板压阻特性的理论研究

考虑量子尺寸效应与自旋轨道耦合作用,从含有应变的6×6 Luttinger-Kohn哈密顿量出发,采用有限差分方法建立了p型硅纳米板的能带结构模型.基于硅纳米板压阻特性与其能带结构的相关性,采用改进的压阻理论定量分析了厚度、杂质浓度与温度对其压阻系数的影响.研究结果表明:量子尺寸效应强烈改变了硅纳米板的能带结构,是其压阻系数增大的主要因素,而自旋轨道耦合作用仅对含较高应变的硅纳米板的能带结构有较大影响;硅纳米板的压阻系数具有尺寸效应,随厚度减小而增大,随杂质浓度增加或温度升高而减小.在高简并条件下,硅纳米板的压阻系数与温度无关,完全由杂质浓度的大小控制;在非简并条件下,情况刚好相反.最后,利用施加应力前后空穴等能面形状的变化定性分析了硅纳米板压阻特性的起源.     

基于共振隧穿二极管的应力检测方法

共振隧穿二极管(RTD)具有微分负阻效应,且其共振隧穿的I-V特性随着廊力的变化而变化,这就是RTD的压阻效应.与半导体材料压阻效应的应用类似,RTD也可用于应力检测.文中研究了两种基于RTD的应力检测方法.在讨论频率-应力检测法的基础上提出了一种新颖的应力检测方法--惠斯通RTD电桥检测法.测试结果表明,基于惠斯通RTD电桥检测法得到的压阻灵敏度随偏置电压可调,町调范围达到三个数量级.     

基于共振隧穿二极管的应力检测方法

共振隧穿二极管(RTD)具有微分负阻效应,且其共振隧穿的I-V特性随着廊力的变化而变化,这就是RTD的压阻效应.与半导体材料压阻效应的应用类似,RTD也可用于应力检测.文中研究了两种基于RTD的应力检测方法.在讨论频率-应力检测法的基础上提出了一种新颖的应力检测方法--惠斯通RTD电桥检测法.测试结果表明,基于惠斯通RTD电桥检测法得到的压阻灵敏度随偏置电压可调,町调范围达到三个数量级.     

Zn_(1-x)Cd_xSe/ZnS量子阱材料的共振遂穿特性研究

本文通过对共振隧穿电流密度随外加偏压及应力而变的依赖关系的理论研究,模拟了Zn1-xCdxSe/ZnS共振隧穿电流密度随外加偏压及应力的变化曲线.给出了等效电阻系数随外加偏压及应力而变的依赖关系,得出了介观压阻系数与外应力的变化符合线性关系的结论.这些结论为将机械信号转换为电学信号的介观效应器件的设计提供了理论指导.     

多晶硅纳米薄膜晶界隧道压阻效应

实验表明重掺杂情况下多晶硅纳米薄膜的应变因子比相同浓度单晶硅的大,且随晶粒尺度减小而增大。为使这种特性在压阻器件中得到合理应用,在分析多晶硅能带结构的基础上,阐明了这种特性根源在于流过晶界的隧道电流随应变而变化引起的隧道压阻效应,给出了晶界压阻系数的计算方法,并从理论上解释了多晶硅纳米薄膜压阻特性的实验现象。     

The short and long term properties of a liquid crystalline polymer at elevated temperatures: Characterization and modeling

Tensile and short term (24 h) creep tests were performed on Xydar G930, a liquid crystalline polymer (LCP) with 30 wt.% glass filler, at temperatures and stress levels ranging from room temperature to 175°C and 0.3 fraction ultimate tensile strength (UTS) to 0.8 fraction UTS, respectively. Temperature was found to have an affect on the short term tensile properties. The resulting strain vs time creep curves showed the expected dependence of creep strain on temperature and stress level. Creep compliance curves were derived from the creep curves and showed distinctively nonlinear viscoelastic behavior at all stress levels and temperatures. Creep compliance was found to follow a power law in time. The power law was used to model the stress dependence of creep and the Arrhenius equation was employed to model the temperature dependence up to 120°C. A significant reduction in creep resistance was observed at 175°C. Time-temperature-stress-superposition was used to show that the material followed power law behavior up to 1000 h.     

Predicted curvature of a glass fiber from the measured curvature ofits coating

An analytical stress model is developed to evaluate the elastic curve of a glass fiber whose coating has a constant (measured or imposed) bend radius. It is shown that in order to predict the bending behavior of a coated glass fiber subjected to bending a parameter u should be computed which depends, in addition to Young's modulus and diameter of the glass fiber itself, also on the length of the curved area and Young's modulus and outer diameter of the (primary) coating. In the range 0<u<2.365, the maximum curvature of the glass fiber occurs at the midpoint of the curved area. If the calculated u value is greater than (7π/4)=5.50, the curvature of the glass fiber in the midportion of the glass-coating composite is practically not different from the coating curvature. Within the range 2.365<u<5.50, the maximum curvature of the glass fiber is greater than the observed curvature of the coating     

Creep Behavior of Bi-Containing Lead-Free Solder Alloys

The creep behavior of Sn-3.0Ag-0.5Cu (SAC305), Sn-3.4Ag-1.0Cu-3.3Bi (SAC-Bi), and Sn-3.4Ag-4.8Bi (SnAg-Bi, all wt.%) was studied in constant-stress creep tests from room temperature to 125°C. The alloys were tested in two microstructural conditions. As-cast alloys had a composite eutectic-primary Sn structure, while in aged alloys the eutectic regions were replaced by a continuous Sn matrix with coarsened intermetallic (Cu₆Sn₅ and Ag₃Sn) particles. After aging, Bi in SAC-Bi and SnAg-Bi was found as precipitates at grain boundaries and grain interiors. The creep resistance of of-cast SAC305 was higher than that of as-cast Bi-containing alloys, but after aging the SAC305 had the lowest creep resistance. The creep strain rates in SAC-Bi and SnAg-Bi were much less affected by aging. The apparent activation energy for creep was also changed more for SAC305 than for the other two alloys. The creep behavior of SAC-Bi and SnAg-Bi can be understood by considering the solubility of Bi in Sn. The difference in creep behavior between as-cast and aged SAC-Bi is greatly reduced when room-temperature test results are excluded from analysis. This suggests that the strongest influence on creep in these alloys is due to Bi solute interaction with moving dislocations during deformation.     

Study on thermal performance of high power LED employing aluminum filled epoxy composite as thermal interface material

This paper elucidates the thermal behavior of an LED employing metal filled polymer matrix as thermal interface material (TIM) for an enhanced heat dissipation characteristic. Highly thermal conductive aluminum (Al) particles were incorporated in bisphenol A diglycidylether (DGEBA) epoxy matrix to study the effect of filler to polymer ratio on the thermal performance of high power LEDs. The curing behavior of DGEBA was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The dispersion nature of the Al fillers in polymer matrix was verified with Field Emission Scanning Electron Microscope (FESEM). The thermal performance of synthesized Al filled polymer composite as TIM was tested with an LED employing thermal transient measurement technique. Comparing the filler to polymer ratio, the rise in junction temperature for 60 wt% Al filled composite was higher by 11.1 °C than 50 wt% Al filled composite at cured state. Observed also from the structure function analysis that the total thermal resistance was 10.96 K/W higher for 60 wt% Al filled composite compared to 50 wt% Al filled composite. On the other hand, a significant rise of 9.5 °C in the junction temperature between cured and uncured samples of 50 wt% Al filled polymer TIM was observed and hence the importance of curing process of metal filled polymer composite for effective heat dissipation is discussed extensively in this work.     

Creep properties of eutectic Sn-3.5Ag solder joints reinforced with mechanically incorporated Ni particles

The creep deformation behavior of eutectic Sn-3.5Ag based Ni particle rein forced composite solder joints was investigated. The Ni particle reinforced composite solder was prepared by mechanically dispersing 15 vol.% of Ni particles into eutectic Sn-3.5Ag solder paste. Static-loading creep tests were carried out on solder joint specimens at 25 C, 65 C, and 105 C, representing homologous temperatures ranging from 0.6 to 0.78. A novel-design, miniature creep-testing frame was utilized in this study. Various creep parameters such as the global and localized creep strain, steady-state creep rate, onset of tertiary creep and the activation energy for creep were quantified by mapping the distorted laser ablation pattern imprinted on the solder joint prior to testing. The Ni-reinforced composite solder joint showed improved creep resistance compared to the results previously reported for eutectic Sn-3.5Ag solder, Sn-4.0Ag-0.5Cu solder alloys, and for eutectic Sn-3.5Ag solder reinforced with Cu or Ag particle reinforcements. The activation energy for creep was ∼0.52 eV for Sn-3.5Ag and Sn-4Ag-0.5Cu solder alloys. The activation energies ranged from 0.55–0.64 eV for Cu, Ag, and Ni reinforced composite solder joints, respectively. Most often, creep fracture occurred closer to one side of the solder joint within the solder matrix.     

变体飞行器柔性复合蒙皮植入式光纤形状传感

针对变体飞行器变形机翼气动外形监测需求,提出一种植入式柔性复合蒙皮形状光纤传感方法。通过将光纤光栅传感器植入硅胶薄层,并与聚氯乙烯薄片组成复合蒙皮。建立柔性蒙皮形状传感系统,采用光纤传感解调系统,实验测得不同翼型下柔性蒙皮中光纤光栅反射谱特征及其变化规律;计算出柔性蒙皮弯曲曲率,并重建出柔性蒙皮变形三维形状;采用数字摄影测量系统完成对比测试。研究结果表明:柔性复合蒙皮变形光纤传感测量与数字摄影测试误差小于4.62%,光纤传感灵敏度达到245.5 pm/m-1。验证了植入式光纤传感方法的有效性,为变体飞行器变形机翼气动外形监测提供了参考。     

In-line fiber etalon (ILFE) fiber-optic strain sensors

This paper describes an optical fiber interferometer that uses a short segment of silica hollow-core fiber spliced between two sections of single-mode fiber to form a mechanically robust in-line optical cavity. The hollow-core fiber is specifically manufactured to have an outer diameter that is equal to the outer diameter of the single mode lead fibers, thereby combining the best qualities of existing intrinsic and extrinsic Fabry-Perot sensors. Uniaxial tension and pure bending strength tests are used to show that the new configuration does not diminish the axial strength of bare fiber and reduces the bending strength by 17% at most. Similar tests confirm that the fiber sensor has 1.96% strain to failure. Axisymmetric finite element analysis is used to investigate the reliability of the in-line etalon when it is embedded in a typical thermoset composite, and parametric studies are performed to determine the mechanically optimal cavity length. The fiber optic sensor is tested using low coherence interferometry with pseudo-heterodyne demodulation under strain and temperature fields. The strain response compares well with resistance strain gages, and the temperature tests confirm the low thermal apparent strain of this sensor     

Highly sustainable mechanical/electrical resistance switching behaviors via one-dimensional Ag/TiO2 core-shell resistive switchable materials in flexible composite

Composite-based resistance switching random access memory (ReRAM) has great potential for application in flexible and wearable electronics. However, its large operating parameters and low reliability still have some limitations in realizing practical applications, which is derived from its high dependence on the orientation and dispersion of the filler in the composite layer. Here, we proposed a novel composite system that does not depend heavily on the orientation or dispersion of the fillers within the composite film of the ReRAM device. The AgNW/TiO₂ core-shell nanowires inducing superb resistance switching behavior were fabricated. The composite resistance switching (RS) film was prepared by mixing the one-dimensional core-shell particles and poly (vinyl alcohol) (PVA) dielectric matrix. The composite RS film exhibited remarkable resistance switching behavior with extremely low/uniform operating voltage (V_set ~ 0.13 ± 0.013 V, and V_reset ~ −0.10 ± 0.012 V), and the reliable switching behavior was maintained for up to ~200,000 mechanical deformation cycles under 3 mm of bending radius. To evaluate the resistance switching mechanism of the composite-type ReRAM, the structural analysis and device modeling were performed.     

Effect of nonconducting filler additions on ACA properties and thereliability of ACA flip-chip on organic substrates

We investigated the effect of nonconducting fillers on the thermomechanical properties of modified anisotropic conductive adhesive (ACA) composite materials and the reliability of flip chip assembly on organic substrates using modified ACA composite materials. For the characterization of modified ACAs composites with different content of nonconducting fillers, dynamic scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and thermomechanical analysis (TMA) were utilized. As the nonconducting filler content increased, CTE values decreased and storage modulus at room temperature increased. In addition, the increase in the content of filler brought about the increase of T_g(DSC) and T_g(TMA). However, the TGA behaviors stayed almost the same. Contact resistance changes were measured during reliability tests such as thermal cycling, high humidity and temperature, and high temperature at dry condition. The reliability results were significantly influenced by CTEs of ACA materials, especially at the thermal cycling tests. Results showed that flip chip assembly using modified ACA composites with lower coefficients of thermal expansion (CTEs) and higher modulus by loading nonconducting fillers exhibited better contact resistance behavior than conventional ACAs without nonconducting fillers