Abstract
Anisotropic conductive adhesives (ACAs) are promising materials used for producing ultra-thin liquid-crystal displays. Because the mechanical response of polymer particles can have a significant impact in the performance of ACAs, understanding of this apparent size effect is of fundamental importance in the electronics industry. The objective of this research is to use a coarse-grained molecular dynamics model to verify and gain physical insight into the observed size dependence effect in polymer particles. In agreement with experimental studies, the results of this study clearly indicate that there is a strong size effect in spherical polymer particles with diameters approaching the nanometer length scale. The results of the simulations also clearly indicate that the source for the increases in modulus is the increase in relative surface energy for decreasing particle sizes. Finally, the actual contact conditions at the surface of the polymer nanoparticles are shown to be similar to those predicted using Hertz and perfectly plastic contact theory. As ACA thicknesses are reduced in response to reductions in polymer particle size, it is expected that the overall compressive stiffness of the ACA will increase, thus influencing the manufacturing process.
Highlights
Because the polymer particles used in Anisotropic conductive adhesives (ACAs) can be subjected to large compressive stresses during the manufacturing process and in-service operation, it is important to understand the influence of large compressive stresses on their mechanical integrity and performance
They used a nanoindentationbased flat punch method to test the compressive response of polymer particles with diameters ranging from 2.6 to 25.1 μm. They observed that decreasing particle diameters resulted in increasing stiffness of the constituent polymer material [6]. This type of size effect has been welldocumented in crystalline, inorganic materials [8,9,10,11,12,13,14], it has not been carefully studied in organic, amorphous materials
Because the mechanical response of the polymer particles can have a significant impact on the performance of ACAs, understanding of this apparent size effect is of fundamental importance in the electronics industry
Summary
Spherical particle molecular models polymer particles can be composed of a wide range of polymer chemistries, linear polyethylene (PE) was chosen as the model material for this study because of its simple conformational structure and the availability of coarse-grained (CG) potentials especially tuned for the surface tension [15]. Experimental research has been previously conducted to determine the mechanical response of micron-sized polymer particles by Zhang et al [5,6,7]. They used a nanoindentationbased flat punch method to test the compressive response of polymer particles with diameters ranging from 2.6 to 25.1 μm. They observed that decreasing particle diameters resulted in increasing stiffness of the constituent polymer material [6]. Because the mechanical response of the polymer particles can have a significant impact on the performance of ACAs, understanding of this apparent size effect is of fundamental importance in the electronics industry
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