Transparent TiO/PMMA hybrids with a thickness of 5 mm and improved refractive indices were prepared by in situ polymerization of methyl methacrylate (MMA) in the presence of TiO nanoparticles bearing poly(methyl methacrylate) (PMMA) chains grown using surface-initiated atom transfer radical polymerization (SI-ATRP), and the effect of the chain length of modified PMMA on the dispersibility of modified TiO nanoparticles in the bulk hybrids was investigated. The surfaces of TiO nanoparticles were modified with both m-(chloromethyl)phenylmethanoyloxymethylphosphonic acid bearing a terminal ATRP initiator and isodecyl phosphate with a high affinity for common organic solvents, leading to sufficient dispersibility of the surface-modified particles in toluene. Subsequently, SI-ATRP of MMA was achieved from the modified surfaces of the TiO nanoparticles without aggregation of the nanoparticles in toluene. The molecular weights of the PMMA chains cleaved from the modified TiO nanoparticles increased with increases in the prolonging of the polymerization period, and these exhibited a narrow distribution, indicating chain growth controlled by SI-ATRP. The nanoparticles bearing PMMA chains were well-dispersed in MMA regardless of the polymerization period. Bulk PMMA hybrids containing modified TiO nanoparticles with a thickness of 5 mm were prepared by in situ polymerization of the MMA dispersion. The transparency of the hybrids depended significantly on the chain length of the modified PMMA on the nanoparticles, because the modified PMMA of low molecular weight induced aggregation of the TiO nanoparticles during the in situ polymerization process. The refractive indices of the bulk hybrids could be controlled by adjusting the TiO content and could be increased up to 1.566 for 6.3 vol % TiO content (1.492 for pristine PMMA).
TiO2nanoparticles (NPs) modified with oleyl phosphate were synthesized through stable Ti–O–P bonds and were utilized to prepare poly(methyl methacrylate)- (PMMA-) based hybrid thin films via theex situroute for investigation of their optical properties. After surface modification of TiO2NPs with oleyl phosphate, IR and13C CP/MAS NMR spectroscopy showed the presence of oleyl groups. The solid-state31P MAS NMR spectrum of the product revealed that the signal due to oleyl phosphate (OP) shifted upon reaction, indicating formation of covalent Ti–O–P bonds. The modified TiO2NPs could be homogeneously dispersed in toluene, and the median size was 16.1 nm, which is likely to be sufficient to suppress Rayleigh scattering effectively. The TEM images of TiO2/PMMA hybrid thin films also showed a homogeneous dispersion of TiO2NPs, and they exhibited excellent optical transparency even though the TiO2content was 20 vol%. The refractive indices of the OP-modified TiO2/PMMA hybrid thin films changed higher with increases in TiO2volume fraction, and the hybrid thin film with 20 vol% of TiO2showed the highest refractive index (n = 1.86).
In this study we propose a new mounting structure for SiC power devices that operate at high temperatures and evaluate its reliability. In this new structure the stress relaxation function rests with the circuit metal on the substrate rather than the joint layer, so high purity aluminum, which has similar characteristics to conventional solder, was chosen as the circuit metal. By conducting a Finite-Element-Method analysis using the measured nonlinear material properties of aluminum, it was possible to make a stress-strain evaluation of the structure. In order to investigate the practical fatigue properties of aluminum we devised a mechanical test method which makes local strain concentration of the chip joint appear, and this method enabled prediction of the thermal fatigue life cycle of the structure. Moreover, a harsh Thermal Cycle Test of the chip mounting samples was conducted between Ϫ50 and 300 degrees Celsius, and a positive correlation was obtained between the predictions and the test results.
To final product quality of mobile phones, key reliability requirements are drop, bend and thermal cycling. Especially in terms of IC-device, drop reliability is the most significant of the three, and also difficult to optimize since it is a dynamic phenomenon in high speed and drop reliability is influenced by 1) system-level factors, 2) board-level and 3) micro-level. In this paper, system-level is defined as phone-level drop, specifically simplified mono-block phone including multiple devices on PWB. System-level enables to evaluate various factors, drop height, drop directions, materials to drop on, phone weight and phone mechanics. Board-level indicates IC-package, PWB and solder joints connecting in between. The board-assembled PWB is fixed onto fixture at 2∼6 points. Drop direction is flat drop only. This paper defines micro level as more detailed model than board level. PWB is modeled as composite structure consisting of dielectric materials with orthotropic properties, copper layers and micro via. IC-package is modeled as well. System level drop shows significant differences in drop directions and also the interactions between drop direction and component location. Micro level simulation results are well-correlative with experimental in failure mode. This paper will discuss overview of 3 levels of drop modeling and will focus on micro level and system level analysis in conjunction with board level.
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