Effects of polymer ball size and polyvinylidene fluoride nanofiber on the ball capture rate for 100-μm -pitch flex-on-flex assembly using anisotropic conductive films and ultrasonic bonding method

There are still many problems in the conductive adhesive, such as particle size and particle dispersion in the matrix, which can affect the stability of the electrical conductivity. In order to resolve the particle dispersion issue in the anisotropic conductive films (ACFs) during the bonding process, we need to increase capture rate of conductive balls between the top and the bottom metal electrodes. In this paper, the methods of increasing capture rates were studied. The capture rates of the conventional 20- and 10- μm polymer ball ACFs were compared. In addition, the capture rates of the conventional polymer ball ACF and polyvinylidene fluoride (PVDF) nanofiber incorporated a polymer ball ACF were compared. As a result, the capture rates of 20- μm polymer ball ACFs were ∼ 30 % higher than 10- μm polymer ball ACFs. And the capture rate of PVDF nanofiber incorporated polymer ball ACF was 21% higher than the conventional polymer ball ACF. By using nanofiber and larger size of conductive balls, the capture rates can be increased.