| With the rapid spread of the global electronics industry, multichip modulepackaging technology is in constant innovation and improvement, mini, multi-functional electronic products packaging technology has received the widespreadattention of scholars both at home and abroad, and high density packagingtechnology, BGA but also for its great advantage has been widely used.Furthermore, with the size of Lead-free solder joints decreasing, which causedthe mechanical, electrical and thermal load had been getting more and moreheavier, study the effective ways to improve the reliability of solder joints isparticularly prominent. In this paper, through different test of the finite elementsimulation method, the mechanical behaviors of BGA solder joints, including thecreep behavior and the cyclic behavior of the shear directions, and differentvariables were analyzed. Meanwhile, the comparative analysis of theexperimental and simulation results of the load-depth curves, extracting thestress-strain variation with time and stress and strain contours, the findings on thedesign and evaluation of the reliability of solder joint have some significance.Through the MSC.Marc software of the finite element analysis method, forthe mechanical behavior of nano-indentation Sn-3.0Ag-0.5Cu lead-free BGAsolder joints were simulated. The analysis proceeds until the load-displacementcurve in good agreement with the experimental curve to verify the reliability ofthe simulation. In addition, a single spot, the distribution of stress and strainthroughout the model in the process of load and unload was uneven, but whichthe stress concentration for the surface contact area of indentation was the mostobvious, the mechanical characteristics of the material does not change in thearea where away from the pushed-in position.Through the one load-unload test of the finite element analysis method, theeffects of the loading rate and hold time for the creep behavior in the shear direction of Sn-3.0Ag-0.5Cu lead-free BGA solder joints were all investigated.The results indicated that the BGA solder joints residual indentation depth, theinternal nonuniform stress and the creep displacement increased the cause of thehold time increasing, the creep rate from big to small finally tended to a constant;with the loading rate increasing, the displacement of the maximum loaddecreased, the creep displacement increased because of the increase of the plasticdeformation of BGA solder joints.Through the cycle load-unload test of the finite element simulation method,the effects of different experimental parameters for BGA solder joints on cyclingperformance of the shear directions were all investigated. The results indicatedthat the cycling performance of Sn-Ag-Cu series Lead-free BGA solder jointswas load-depth, and the cumulative damage of BGA solder joints was increasedwith the increase of maximum load, especially largely accumulated in the firstfew cycles, its final residual indentation depth and area were significantlyincreased; the creep displacement of BGA solder joints contained in Bulgariafirst stabilized after a sharp increase, the performance of the residual indentationdepth and hysteresis loop area increased dramatically after the first flatten; theindentation depth appreciation of BGA solder joints was gradually decreasingwith the increase of the number of cycles, reaction to plastic deformation,damage accumulation were increasing.Through the finite element simulation method, the internal stress of of BGAsolder joints in the shear direction showed that: in the role of cyclic loading, thecontact area of solder joints and the pressure (around the indentation edge) wasthe largest stress, the damage accumulation was increasd with the increasing ofthe maximum load and the number of cycles, so the dislocation was too late toclimb which causes the significant folds phenomenon. |
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