Elastic region of an ACF joint for thermosonic flip-chip bonding

In this paper, a thermosonic flip-chip bonding method using vibration in the lateral direction is proposed. To enhance the reliability and alignment of the specimen after the thermosonic process, an elastic region of anisotropic conductive film (ACF) joints is investigated, within which ultrasonic vibration is applied. By creep-recovery tests, it is shown that the elastic region gradually develops up to 7 µm as the degree of cure increases to 90%. Based on this result, a two-step lateral thermosonic process composed of a pure thermal curing process at the viscoelastic stage of the ACF epoxy and a thermal and ultrasonic curing process within an established elastic region is proposed. To demonstrate the feasibility of the proposed approach in practice, experiments with a commercialized ACF and LCD driver chips are conducted. The experiment shows a notable enhancement in the alignment of the specimen after the thermosonic process, with a bonding time reduction of 33.3% compared with the conventional thermocompression process