The Study Of Interface Morphology Change Of Micro Solder Joints During Aging And The Simulation Study Of Its Impact On Performance

With the trend of miniaturization and high performance of the electronic products,the solder joints become smaller and smaller, and has put forward higher requirements tothe reliability of micro-connection technology. During the process of service, themicrostructure change of solder joints, especially the morphology change of IntermetallicCompound (IMC), has a great impact on solder joints mechanical properties andreliability. As the decreasing of the solder joints size, the proportion of IMC is increasing,this makes the IMC has a more important impact on the solder joints performance.Therefore, the research on the IMC microstructure change of micro solder joints underaging condition and the impact of IMC morphology change on the micro solder jointsperformance is important.In this paper, the IMC microstructure change of aging solder joints, which had astructure of polycrystalline Cu/SAC305/polycrystalline Cu, was studied. The resultsshow that, during aging process, the rate of IMC thickening is proportional to the squareroot of the aging time; the interface roughness of IMC/solder is inversely proportional tothe aging time; the trend of Kirkendall voids presents from disperse growth to aggregategrowth.On the basis of the experiments,2D finite element models were established tosimulate the impact of different IMC thickness, interface roughness and Kirkendall voidson stress distribution. The results show that: the IMC thickness has no significant effecton the stress distribution; when the interface roughness is larger than1.4μm, the stressgenerated during tensile test will be dispersed, so that the solder internal stress willbecome uniform; stress will concentrate around the Kirkendall voids, and the aggregationand combination of the Kirkendall voids have a great impact on the value of themaximum stress. The results of tensile test and simulation show that: when the agingtime is less than500h, the tensile strength of solder joints is determined by solder tensilestrength; when the aging time is larger than500h, the tensile strength of solder joints is effected by IMC strength, so during aging process, the tensile strength of solder joint willshow an increase trend first and then decrease.Finally, finite element models were used to study the impact of different IMCthickness and interface roughness on the thermal cycle fatigue life of the solder joints.The results show that: when IMC thickness increases or when the interface roughnessdecreases, the equivalent plastic within solder will increase, so that the fatigue life ofsolder joints reduces significantly.