The processing of a new series of liquid crystalline (LC) epoxy networks was evaluated. Above the glass transition temperature, the low crosslink density networks could be mechanically aligned. The mechanically oriented networks readily lost orientation upon heating. Highly anisotropic liquid crystalline (LC) epoxy networks were also prepared by aligning the mesophase of the prepolymer during the curing process under the influence of a magnetic field. Orientation parameters (f) of 0.13 to 0.57 were achieved by these processes as determined by x‐ray diffraction analysis. The ability of the magnetically aligned networks to retain their orientation above the glass transition temperature was determined by time‐resolved x‐ray diffraction. The stability of the alignment of these networks was found to depend on crosslink density. The effect of the anisotropy of these networks was investigated by measuring the coefficient of thermal expansion (CTE). In the aligned networks, there was a substantial reduction in CTE parallel to the direction of the applied field compared to the randomly oriented networks. © 1992 John Wiley & Sons, Inc.
This article describes the synthesis and characterization of a new series of liquid crystalline thermosets. Nematic epoxy‐terminated oligoethers based on dihydroxy‐α‐methylstilbene were synthesized for this study. These prepolymers were crosslinked within the nematic mesophase using methylenedianiline. Depending upon the molecular weight and polydispersity of the oligoether, the crosslinking reaction resulted in networks with either a smectic or nematic molecular organization in contrast to the simple nematic phase of the oligoether. The formation of a smectic‐like structure on curing was found to be related to the breadth of the prepolymer molecular weight. In those networks with a low crosslink density a clearing transition could be observed, whereas in the more highly crosslinked networks the molecular organization was frozen in until decomposition. The glass transition temperature of these LC networks rose as the crosslink density was increased, ranging from 35 to 152°C. In agreement with theory, the clearing transition of the networks was found to be dependent on the phase state during curing © 1992 John Wiley & Sons, Inc.
Polymers have found wide usage in microelectronics industry. Their moisture absorption properties cause the concern of reliability without hermeticity (RwoH). For printed circuit packages, the lamination process, the components assembly, and the field performance of final product are strongly influenced by the presence of high level moisture content. For instance, moisture is an important factor in the development of internal shorts through metal migration when printed circuit package is in service. Moisture can also cause dimensional changes in printed circuit cores and delamination during the soldering processes in components assembly, resulting in manufacturing yield loss and defects. Understanding moisture properties of resins and the resin glass composites are therefore important in developing a strategy to control the moisture content of final products. This paper will discuss the moisture fundamental properties of two resins and their resin glass systems. These properties will be related to their assembly and reliability performance.
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