| As a new type of environment-friendly electronic interconnect material,conductive adhesive has the advantages of low curing temperature,good connectivity and simple process,so it has a broad application prospect in portable electronic products.However,electronic products are easy to bear drop impact in the process of production and service,resulting in a relatively high strain rate at the bonding point of tiny conductive adhesive.The research on the mechanical behavior and reliability of conductive adhesive under high strain rate is particularly important.Therefore,in this paper,two kinds of epoxy resin based isotropic conductive adhesive（ICA）with different silver contents（50wt.%and 60wt.%）were used as research objects,and a universal testing machine and a split Hopkinson pressure bar were used to carry out static and dynamic mechanical properties experimental study on the cylindrical samples of cured ICA and its double overlap shear samples.Combined with numerical simulation,the dynamic mechanical response of the bonding point of the conductive adhesive interconnection package structure under drop impact was analyzed.The relevant research contents and conclusions are as follows:（1）The quasi-static compression tests of two kinds of silver content cured ICA cylindrical samples at two strain rates of 0.01 s-1 and 0.1 s-1were carried out by the universal testing machine,and the dynamic compression tests of two kinds of silver content cured ICA cylindrical samples at three strain rates(about 1100 s-1,2100 s-1 and 3200 s-1)were carried out by the split Hopkinson pressure bar.Whether the two kinds of silver content cured ICA have strain rate effect was analyzed;in addition,the effect of silver particle content on the stiffness and yield strength of the cured ICA was analyzed,and the Cowper Symonds strain rate dependent constitutive model of the cured ICA was given accordingly.The results show that the two cured ICAs have no obvious strain rate effect under quasi-static compression,but have obvious strain rate effect under dynamic compression;the overall stiffness and yield strength of high silver content cured conductive adhesive are higher than that of low silver content cured conductive adhesive,and its strain rate effect is more obvious.（2）The quasi-static compression shear tests were carried out on the double lap shear specimens of two kinds of silver content ICA and red copper blocks by using the universal testing machine,and the dynamic compression shear tests were carried out on the double lap specimens at three loading speeds（2 m/s,3 m/s and 4 m/s）by using the separated Hopkinson pressure bar.The loading rate effect of the two kinds of silver content cured ICA was analyzed,The effect of silver particle content on the shear bonding strength of cured ICA was also analyzed.The results show that compared with low silver content ICA,the shear strength of double lap shear specimen of high silver content ICA is lower under quasi-static low loading rate,but it is higher under dynamic high loading rate,and its loading rate effect is more obvious.（3）The finite element model of free drop of ICA interconnection packaging structure was established and the mechanical behavior of drop impact of ICA interconnection packaging structure was studied through numerical simulation.The stress generation mechanism and the location of the key bonding point were analyzed.The stress and deformation of ICA interconnection points under horizontal drop and small-angle drop impact were analyzed.The results show that the stress deformation of ICA interconnection points is mainly caused by the bending deformation of PCB board,and the key bonding joint appears at the four corners of the package;the horizontal drop is not the most dangerous working condition,while the small-angle drop is relatively easy to cause the damage of adhesive joints;the long-side drop mode results in a relatively large stress and strain at the key bonding point in comparison with that of the short-side drop mode. |
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