Isotropic Conductive Adhesive Conductive Mechanism And Its Volume Resistivity Calculated

Based on two kinds of silver powder with different morphology and three matrixes with different curing shrinkage, six electrical conductive adhesives were prepared. During the curing of these six electrically conductive adhesives, the change of volume resistivity was studied. And the qualitative analyses of the contribution of the factors to the conductivity establishment and the effect on the volume resistivity of electrically conductive adhesive were obtained. In addition, the resistance change of silver powders in the process of being compressed was studied. The following results can be summarized.(1) Comparatively speaking, the results showed that the morphology of silver powder had less influence on the conductivity, while the curing shrinkage of the matrixes contributed more to the conductivity developments and played a crucial role in the process of conductivity achievement.(2) The volume resistivity of conductive adhesive before cure was seemed to be insulated due to the high resistivity. A power law dependence of the volume resistivity upon curing time is found in the whole curing process.(3) The volume of matrix constantly changed and decrease monotonously during the curing process. There was an exponential relationship between volume change and curing time. On the one hand, the silver powders were packed more closely with the curing shrinkage of matrix, thus increasing the contact area and decreasing the contact resistance. On the other hand, the distance of powders which apart from each other became smaller so that the pairs of the contacted powders may increase. The occurrence probability of tunnel effect during those uncontact powders may increase too, so as to increase the electric conduction circuit and increase the conductivity of the conductive adhesive system. Eventually, with the common effect of above factors, the conductive adhesive achieved conductive from insulated while the resistance dropped sharply during the curing process. The resistance change of silver powders in the process of being compressed further explained that the constantly reduce of the resistance of conductive adhesive during curing process owing to silver powder compacted more closely on the effect of curing shrinkage.(4) The system of conductive adhesive can be regarded as a three-dimensional conductive network whose size is similar to conductive adhesive. The resistance of conductive network is equal to that of the conductive adhesive. The three-dimensional conductive network can be divided into a number of two-dimensional conductive networks. And the two-dimensional conductive network can be divided into a number of one-dimensional conductive circuits which consist of a series of silver powder couple.(5) Based on the contacted silver powder couple, introducing some terms such as contact aera, contact force, constriction resistance, tunneling resistance, intrinsic resistance and derivation of these concept, a formula for calculating the volume resistivity of conductive adhesive in an ideal state was derivated and it was modified by some experiment results. The final form is:whereη_vs is the curing shrinkage; r is the radius of silver powder, m; V_f is the volume fraction; R_p is the resistance of silver powder couple,Ω.