No abstract

Although polymer-based materials are widely used in microelectronics packaging and viscoelasticity is an intrinsic characteristic of polymers, viscoelastic properties of polymeric materials are often ignored in package stress analyses due to the difficulty in measuring these properties. However, it is necessary to consider the viscoelastic behavior when an accurate stress model is required. Viscoelastic properties of materials can be characterized in either the time or the frequency domain. In this study, stress relaxation experiments were performed on a molding compound in the time domain. A thermorheologically simple model was assumed to deduce the master curve of relaxation modulus using the time-temperature equivalence assumption. A Prony series expansion was used to express the material's relaxation behavior. Two methods to determine the Prony pairs and shift factors were compared. After they were determined, the master curve at a reference temperature was shifted to every measured temperature for comparison with experimental data.

A new porphyrin-based Co-MOF, [Co(DpyDtolP)] 6 ·12H 2 O (I) composed of DpyDtolP (5,15-di(4-pyridyl)-10,20-di(4-methylphenyl)porphyrin) was prepared in a high yield and structurally characterized by X-ray crystallography. DpyDtolP is a ditopic N-donor ligand with a large space or gap between the two pyridyl groups at the 5-and 15-positions of the porphyrin backbone. Unlike the pyridyl groups, the 4-tolyl groups in DpyDtolP could not be involved in coordination toward the metal ion. Nevertheless, the presence of these two 4-tolyl groups led to a new infinite three-dimensional framework: Co-MOF (I) with exceptionally high thermal stability at elevated temperature. The single crystals of I maintained their crystallinity even after vacuum drying at 250 °C. The resulting dried single crystals diffracted X-ray to give the same structural solution as the as-prepared crystals. The robust framework of I contained micropores that were periodically arranged in a hexagonal symmetry. While the evacuated I moderately sorbed N 2 at 77 K, it sorbed 142.8 cm 3 g -1 (6.37 mmol g -1 ) of CO 2 at 196 K. The CO 2 sorption isotherms exhibited a very clear step in both the adsorption and desorption branches. A slight hysteretic behavior was observed between the two branches. Furthermore, the crystal structure of CO 2 captured I (I_CO 2 ) revealed that the linear arrangement of the CO 2 molecules occupying the inside of micropores, thereby indicating the effective CO 2 capture by evacuated I.The evacuated I was also found to be ideal for the encapsulation of iodine molecules in cyclohexane to provide iodine-captured I (I_I 2 ), which was also characterized by X-ray crystallography. The linear arrangement of polyiodine chains in the micropores was observed, and a single crystal of I_I 2 exhibited electrically conducting behavior. The encapsulation amount of iodine was dependent on the crystal sizes of I. Additionally, the separately prepared microscale sample, micro-I, with a much reduced particle dimension than the bulk I exhibited an enhanced uptake of iodine under the same conditions.

No abstract

No abstract