Research On Mechanical Behavior Of Buckling For CuCGA Interconnect Structure

With the development for miniaturization and functional diversification of electronic products,the requirement of reliability for electronic packaging devices was constantly improving.At present,the reliability of Ball Grid Array?BGA?packaging which was proposed to meet the requirement of high density and miniaturization was significantly lower than quad flat non-leaded?QFN?packaging.The reliability of Ceramic Column Grid Array which was developed by IBM was higher than the packaging devices with BGA.In order to adapt to the trend of leadfree electronic products,soldering columns were replaced by copper columns forming copper column grid array?Cu CGA?interconnect structure.In recently,the research of Cu CGA interconnect structure mainly focuses on the reliability of the structure thermal cyclic loading,and the failure of the structure under the condition of mechanical loading was less.In order to comprehensively study the effect of shape-parameters to the carrying capacity of Cu CGA under various forms of loading,the paper studied the processing of buckling of Cu CGA interconnect structure based on the theory of linear and nonlinear buckling analysis with the help of finite element simulation software MSC.Marc.The mechanical behavior of copper soldering column and shape-parameters of Cu CGA?including copper column L/D ratios,the heights of soldering fillet and copper pad center distance?in the Cu CGA interconnect structure under vertical pressure were studied in the paper,the conclusions were as follows:1.Before the buckling of Cu CGA interconnect structure,the stress distribution of the Von Mises stress of Cu soldering column is uniform,and the Von Mises stress of Cu column was significantly larger than that of the Von Mises stress in the soldering fillet.The distribution of Von Mises stress for soldering fillet showed centered by copper column axis then decrease gradually;when the buckling ofCu CGA interconnect structure,the distribution of Von Mises stress of Cu column and soldering fillet were broken,also the distribution of Von Mises stress near area of the middle cross section for Cu column;Compared with the deformation of each Cu soldering column in the Cu CGA interconnect structure,it can be seen that the bending direction of Cu soldering column is different,which shows the random characteristic of buckling deformation.2.When the height of soldering fillet is 0.33 mm,diameter of soldering pad is1.0 mm,and the diameter of Cu column is 0.32 mm,with the increasing of L/D for copper column from 5 to 16.5,the critical load and the stress of the Cu CGA interconnect structure decreased.The difference between perturbation buckling analysis and arc length method buckling analysis theory is little.According to nonlinear?perturbation?buckling analysis,before the buckling of Cu column with L/D from 5 to 11.5,soldering fillet of weakness performance occurred micro crack for the local region tensile stress exceed the ultimate strength of the soldering fillet;Cu column with L/D from 11.5 to 16.5 buckle firstly.Considering the reliability of soldering fillet with local microcrack and the buckling failure of Cu soldering column,the relationship equation between L/D ratio of Cu column and critical stress of Cu CGA interconnection structure was established.The axial critical stress was almost constantly for Cu column with L/D from 5 to 11.5,and in the range of 11.5 to16.5,critical stress decreased by proportional to the law of ?₀^-2,which is in accordance with the Euler formula describe the large flexibility.3.When the L/D ratio of Cu column is 10,with the increasing of the height of soldering fillet,the critical load of Cu CGA interconnect structure increase significantly,and with the increasing of the distance of Cu pad center,the critical load of Cu CGA interconnect structure reduced slightly.The failure of Cu CGA with different height of soldering fillet and distance of Cu pad center was similarity.It's that the peak stress of Cu soldering fillet is higher than that of the soldering,which leads to the micro crack in the soldering column that reduce the reliability of the structure.