High-powered thermal gel degradation evaluation on board-level HFCBGA subjected to reliability tests

HFCBGA is a thermally enhanced FCBGA with its heat spreader extending the heat conduction area by connecting itself to the rear side of the silicon die. A thermal interface material plays an important role as a heat conduction path. The thermal performance should not only be checked at time zero, and several reliability tests have to be undertaken to uncover the field conditions faced by end users. A temperature cycling test, highly-accelerated temperature and humidity stress test and multiple reflows are utilized to investigate the thermal resistance of junction to case of a selected thermal gel.     

自写入光波导聚合物微透镜阵列的设计与制作

利用聚合物SU-8光刻胶在激光作用下折射率会发生变化的特点,将其作为最后的光学材料,采用光刻胶热熔法和图形转移法,设计并制作了填充因子接近0.75、自写入光波导、六角排列的微透镜阵列。对阵列的表面形态、三维结构和光学性能分别进行了观察、测试与分析,发现用SU-8胶制作的微透镜阵列外观良好,边缘清晰;自写入光波导微透镜阵列的三维结构良好;波导末梢的光点分布均匀,光强一致性高。这种自写入光波导的微透镜阵列降低了透镜阵列与探测阵列精确装配的难度,而且其制作工艺流程简单、成本低廉、适合批量复制,这种阵列元件还有质量轻、体积小的特点,有很广的应用前景。     

Effects of Minor Amounts of Zn on the Sn-Zn/Ni Interfacial Reactions and Phase Equilibria of the Ternary Sn-Zn-Ni System at 250°C

This study investigated the effects of minor Zn additions (less than 1 wt.%) to pure Sn on the phase formation and microstructural evolution at the interfaces between Ni and Sn-Zn solders. When the Zn content was less than 0.3 wt.%, the reaction product was Ni₃Sn₄, which had no Zn solubility. By contrast, for reactions with more than 0.4 wt.% Zn, one high-Zn-containing phase (about Sn-35 at.%Ni-20 at.%Zn) was formed, which was proven to be a ternary intermetallic compound, the τ-phase. In addition to composition analysis, x-ray diffraction (XRD) analysis revealed that the crystallographic structure of the τ-phase was different from that of Ni₃Sn₄. Furthermore, a partial isothermal section in the Sn-Zn-Ni ternary system (less than 40 at.% Ni) at 250°C was experimentally determined to contain 12 different Sn-Zn-Ni alloys. Three three-phase regions were identified: Ni₃Sn₄ + τ + liquid, Ni₅Zn₂₁ + τ + liquid, and Ni₅Zn₂₁ + Zn + liquid. The equilibrium phase boundaries for liquid separately with Ni₅Zn₂₁, τ, and Ni₃Sn₄ were highly consistent with the Zn concentrations where the phase transitions occurred in the interfacial reactions.     

Discrimination of breast cancer by measuring prostate-specific antigen levels in women's serum

Prostate-specific antigen (PSA) has been reported to be a potential biomarker of breast cancer. Serum PSA of normal women is around 1 pg/mL, which is usually undetectable by current assay methods; thus an ultrasensitive measurement of PSA expression in women's serum is necessary to distinguish normal from malignant breast diseases. To enhance the sensitivity of conventional immunoassay technology for the detection of PSA in sera, we adopted a localized surface plasmon coupled fluorescence fiber-optic biosensor, which combines a sandwich immunoassay with the localized surface plasmon technique. The concentration of total PSA (t-PSA) (from 0.1 to 1000 pg/mL) in phosphate-buffered saline solution and the normalized fluorescence signal exhibit a linear relationship where the correlation coefficient is 0.9574. In addition, the concentration of additional t-PSA in 10-fold-diluted healthly women's serum across a similar range was measured. The correlation coefficient for this measurement is 0.9142. In clinical serum samples, moreover, the experimental results of t-PSA detection show that both the mean value and median of normalized fluorescence signals in the breast cancer group (155.2 and 145.7, respectively) are higher than those in the noncancer group (46.6 and 37.1, respectively). We also examined the receiver operating characteristic curve for t-PSA, and the area under the curve (AUC) is estimated to be 0.9063, the AUC being used to measure the performance of a test to correctly identify diseased and nondiseased subjects.     

Periodic solutions of multi-degree-of-freedom strongly nonlinear coupled van der Pol oscillators by homotopy analysis method

The mathematical models of multi-degree-of-freedom (MDOF) strongly nonlinear dynamical systems are described by coupled second-order differential equations. In general, the exact solutions of MDOF strongly nonlinear dynamical systems are frequently unavailable. Therefore, efforts have been mainly concentrated on the approximate analytical solutions. The homotopy analysis method (HAM) is a useful analytic tool for solving strongly nonlinear dynamical systems, and it provides a simple way to ensure the convergence of solution series by means of a convergence-control parameter ${\hbar}$ . Unlike the classical perturbation techniques, this method is independent of the presence of small parameters in the governing equations of motion. In this paper, the HAM is applied to formulate the analytical approximate periodic solutions of MDOF strongly nonlinear coupled van der Pol oscillators. Within this research framework, the frequency and the displacements of two-degree-of-freedom (2-DOF) strongly nonlinear systems can be explicitly obtained. For authentication, comparisons are carried out between the results obtained by the homotopy analysis and numerical integration methods. It is shown that the fourth-order or eighth-order solutions of the present method provide excellent accuracy. Illustrative examples of three-degree-of-freedom (3-DOF) strongly nonlinear coupled van der Pol oscillators are also presented and discussed. Finally, the optimal HAM approach is used to accelerate the convergence of the solutions.     

Analytical approximate periodic solutions for two-degree-of-freedom coupled van der Pol-Duffing oscillators by extended homotopy analysis method

In this study, the extended homotopy analysis method (EHAM) is applied to derive the accurate approximate analytical solutions for multi-degree-of-freedom (MDOF) coupled oscillators. The present paper not only introduces the rationale for the EHAM for MDOF oscillators, but also strengthens the availability of the conventional homotopy analysis method (HAM) in solving complex MDOF dynamical systems. Employing the EHAM for the two-degree-of-freedom (TDOF) coupled van der Pol-Duffing oscillator, the explicit analytical solutions of frequency ?? and displacements x ₁(t) and x ₂(t) are formulated for various initial conditions and physical parameters. To verify the accuracy and correctness of this approach, a number of comparisons are conducted between the results of the EHAM and the numerical integration (i.e. Runge-Kutta) method. It is shown that the third-order analytical solutions of the EHAM agree well with the numerical integration solutions, even if the time variable t progresses to a comparatively large domain in the time history responses.     

Matrix interference-free method for the analysis of small molecules by using negative ion laser desorption/ionization on graphene flakes

This work presents a new approach for the analysis of small molecules with direct negative ion laser desorption/ionization (LDI) on graphene flakes. A series of matrix interference-free mass spectra were obtained for the analysis of a wide range of small molecules including peptides, amino acids, fatty acids, as well as nucleosides and nucleotides. The mixture of analytes and graphene flakes suspension were directly pipetted onto a sample plate for LDI-time-of-flight mass spectrometry (TOFMS) analysis. Deprotonated monomeric species [M-H](-) ions were homogeneously obtained on uniform graphene flakes film when negative ion mode was applied. In positive ion mode, the analytes were detected in form of multiple adduct ions such as sodium adduct [M+Na](+), potassium adduct [M+K](+), double sodium adduct [M+2Na-H](+), double potassium adduct [M+2K-H](+), as well as sodium and potassium mixed adduct [M+Na+K-H](+). Better sensitivity and reproducibility were achieved in negative ion mode compared to positive ion mode. It is believed that the new method of matrix interference-free negative ion LDI on graphene flakes may be expanded for LDI-MS analysis of various small molecules.     

Laser ablation of silicon using a Bessel-like beam generated by a subwavelength annular aperture structure

Using a femtosecond laser incident to an oxide-metal-oxide film engraved with a subwavelength annular aperture (SAA) structure, we generated a Bessel-like beam to ablate silicon. Experimental results show that the silicon can be ablated with a 0.05 J/cm(2) input ablation threshold at 120 fs pulse duration. We obtained a surface hole possessing a diameter less than 1 μm. Optical performance, including depth-of-focus and focal spot of the SAA structure, were simulated using finite-different time-domain calculations. We found that a far-field laser beam propagating through a SAA structure possesses a submicrometer focal spot and high focus intensity. Our method can be easily adopted for surface machining in microfabrication applications.     

Fabrication of three-dimensional polymer quadratic nonlinear grating structures by layer-by-layer direct laser writing technique

We demonstrate the fabrication of a three-dimensional (3D) polymer quadratic nonlinear (χ(2)) grating structure. By performing layer-by-layer direct laser writing (DLW) and spin-coating approaches, desired photobleached grating patterns were embedded in the guest-host dispersed-red-1/poly(methylmethacrylate) (DR1/PMMA) active layers of an active-passive alternative multilayer structure through photobleaching of DR1 molecules. Polyvinyl-alcohol and SU8 thin films were deposited between DR1/PMMA layers serving as a passive layer to separate DR1/PMMA active layers. After applying the corona electric field poling to the multilayer structure, nonbleached DR1 molecules in the active layers formed polar distribution, and a 3D χ(2) grating structure was obtained. The χ(2) grating structures at different DR1/PMMA nonlinear layers were mapped by laser scanning second harmonic (SH) microscopy, and no cross talk was observed between SH images obtained from neighboring nonlinear layers. The layer-by-layer DLW technique is favorable to fabricating hierarchical 3D polymer nonlinear structures for optoelectronic applications with flexible structural design.     

Synthesis and properties of solution-processible oligomers for the use of organic light-emitting diodes (OLEDs)

Two oligomers with X-shaped repeating units bearing anthracene and fluorene units were synthesized in a facile procedure, and exhibited high photoluminescence efficiencies, thermal stabilities and good solubility. Their ease of processing enabled spin coating with an electron-transporting bitriazine layer to afford organic light-emitting diodes which displayed a light blue emission with the maximum luminance of 3650 cd/m² and the current efficiency of 0.69 cd/A at an operation voltage of 10 V.