Effect of Nanofiber Orientation on Nanofiber Solder Anisotropic Conductive Films Joint Properties and Bending Reliability of Flex-on-Flex Assembly

Anisotropic conductive films (ACFs) have been widely used as an interconnection adhesive material due to its light weight and simple and low-temperature assembly processes. However, because of the higher demands for further miniaturization, short-circuit problem of ACFs interconnection has been a major issue, when it comes to very fine pitch assembly. Also, due to the fast development of wearable devices, demands for flexible packaging as well as flexible interconnection methods such as flex-on-flex (FOF) are growing more, where the bending characteristics are important. Nanofiber incorporated ACFs were previously introduced by our research group. The nanofiber incorporated ACFs showed excellent conductive particle movement suppression capability that not only prevents short circuit but also improves the conductive ball capture rate, which eventually improves the joint reliability of fine pitch FOF assembly. In order to maximize the conductive particle movement suppression capability of the nanofiber, nanofiber was oriented using a drum-type receiver. In addition, the bending reliability of FOF assembly using nanofiber/solder ACFs with different nanofiber orientations has been also investigated. As a result, parallel nanofiber/solder ACFs showed excellent joint properties as well as bending reliability due to the stable metallurgical solder joint formation and high conductive particle movement suppression capability, and this new type of ACF technology will provide a promising solution for future flexible electronic packaging.