Study On Thermodynamics Behavior Of SMT Solder Joints

Anand viscoplastic constitutive model is used to describe the behavior of eutectic BGA solder (Pb90Sn10). With the change of solder joint shape including drum, concave and column, under the thermal loading, stress/strain distribution is studied in FEM. And also the relations of pad size, spot spacing and distributing pattern of the solder joint to stress/strain distribution are investigated .The research finds:1. Whatever shapes of solder joints, under the thermal loading, the distribution of the largest equivalent Von Mises stress/strain are all approximately same which is in the brim of solder close to the joint of solder and PCB. Based on the analyzing the whole model, the research finds that the largest equivalent Von Mises stress is in the center of silicon which is the joint of silicon and solder, and the largest equivalent Von Mises strain is distributed around the brim of solder close to the joint of solder and PCB. And for solder, both the largest equivalent Von Mises stress and strain are distributed the outer of solder close to the joint of solder and PCB. The lower the height of arc is, and the smaller the depth of arc is, the better reliability of solder joints has.2. Under the thermal loading, the concave joint is the most reliable among all shapes of solder joints.3. Under the thermal loading, the largest equivalent Von Mises strain of solder joints is reduced as the decrease of the pad size. The distribution curve of spot spacing and strain is normal, that is to say, smaller and the longer distance between solder joints has, the smaller the largest equivalent Von Mises strain is.4. At present solder joints are distributed with equidistant square array. A sort of solder joints that is arranged by regular hexagon array mode is studied. It is found that the packing density of regular hexagon array, with no change of the distance between solder joints, is higher than that of the solder joints with equidistant square array, andunder the thermal loading the largest equivalent Von Mises stress/strain of the solder joints with regular hexagon array is less than that of with equidistant square.