Loading Rate Effect On Shear Mechanical Properties Of Isotropic Conductive Adhesives

Since the lead-free development of electronic packaging,lead-free solder and conductive adhesive have been the major interconnected materials.Compared with the traditional alloy solder,the conductive adhesive has the advantages of low process temperature,good connectability and simple operation,etc.With the wider application of conductive adhesives,research and development of its products and related mechanical properties during service have attracted widespread attention in the industry.In the production,transportation and use of electronic products,the main cause of adhesive failure is due to shear damage.At present,there are relatively few studies on the shear mechanical properties of isotropic conductive adhesives under different loading rates.Therefore,an isotropic conductive adhesive with a silver mass fraction of 60 wt.% was used.The T2 copper plate was used as the bonding adherent to make an experimental specimen with single lap joints.The tensile shear experiments at different loading rates were carried out on the single lap joint specimens of isotropic conductive adhesives.The shear mechanical behavior and stress distributed in the adhesive layers of the conductive adhesives at different loading rates were theoretically deduced and analyzed.Then,based on the finite element simulation,the correctness of shear stress distribution theory in the conductive adhesive layer was verified.The related research contents and conclusion is as follows:(1)INSTRON 5544 universal material testing machine was used for tensile–shear tests of isotropic conductive adhesive joint specimens.Four loading rates,that is,0.05,0.5,5,and 10 mm/min,were adopted.The relationship between shear load and displacement of two overlapping copper plates is deduced from a mechanical perspective.A mechanical model of the conductive adhesive shear specimen was developed by introducing dimensionless parameters A and B,which are obtained from interfacial fracture energy and shear strength,to interpret the effect of loading rate on the shear properties of the conductive adhesive specimen considering the loading rate.Results show that this model can effectively reflect the relationship between shear load and displacement in the range of 0.05~10 mm/min.And using experiments to verify the relevant,found that the theoretical results and experimental results are in good agreement.It is of referential significance to the design and manufacture of adhesion devices in electronic packaging industry.(2)In order to study the phenomenon of stress distribution in the adhesive layer more scientifically,based on the tensile shear test of conductive adhesives,the shear stress at various positions in the conductive adhesive layer was theoretically deduced,and the shear in the conductive adhesive layer was found.The relationship between shear stress and the location of the adhesive layer presents a hyperbolic function form.At the same time,the commercial finite element software ANSYS16.0 was used to simulate and verify this theory.Then the extracted data and the theoretical results were compared and found to be in good agreement.The measures to reduce the stress concentration in conductive adhesive layer are put forward.It provides theoretical guidance for the design and manufacture of electronic packaging industry.