Study On Interface Reaction And Reliability Of SAC/Co-P BGA Solder Joints Under Rapid Thermal Fatigue

With the rapid development of electronic technology and artificial intelligence,the miniaturization,integration and high power of electronic components have become the mainstream of the times.In the long-term service process,BGA Solder Joints will bear high frequency and sharp temperature changes,which will lead to thermal fatigue reliability problems.It is found that Co-P UBM is expected to be a substitute for traditional Cu UBM due to its excellent diffusion barrier,acceptable wettability and excellent anti electromigration performance.Therefore,the research on interface reaction and reliability of Co-P/Solder BGA Solder Joints as a new UBM interconnection mode under rapid thermal fatigue is of great significance to improve the reliability of solder joints in actual service.In this paper,the effect of P content on the interface of SAC/Co-P in BGA Solder Joints under rapid thermal fatigue loading was studied.Based on the evolution of interface reaction and fatigue crack,Cu/SAC/Co-P and Co-P/SAC/Co-P flip chip solder joints were prepared by Co-P UBM with high reliability,and the interaction of interface reaction and fatigue crack evolution of flip chip solder joints under rapid thermal fatigue were further studied.Finally,combined with the shear strength and fracture failure mechanism of solder joints,the thermal fatigue reliability of solder joints under different Co-P UBM was compared and analyzed,and the reliability and development prospect of solder joints under new Co-P/SAC interconnection under rapid thermal fatigue were evaluated.In the SAC/Co-P solder joint structure,with the increase of rapid thermal fatigue cycle.In the Co-5%P interface reaction,the IMC of the interface gradually changes from the initial layered Co Sn₃ to the flat(Cu,Co)₆Sn₅+Co Sn₃IMC mixed structure.In the Co-13%P interface reaction,the irregular distribution of tile like Co Sn₃at the interface gradually peels off from the interface and dissolves into the solder,resulting in the new formation of massive Co Sn₃ at the end of rapid thermal fatigue IMC shows discontinuous block distribution.In the Co-20%P interface reaction,Sn can rapidly diffuse at the Co-P interface to form a Co-Sn-P layer,and the interface IMC gradually transforms from a dense tile like Co Sn₃ and a flat Co-Sn-P layer to a flat Co Sn₃+(Cu,Co)₆Sn₅+Co-Sn-P IMC mixed structure.In the control group,with the increase of rapid thermal fatigue cycle,the scallop like interface IMC gradually becomes flat,and the interface IMC is still Cu₆Sn₅.The results show that the SAC/Co-13%P solder joint has good thermal fatigue reliability,and no crack growth is found under rapid thermal fatigue loading.In the study of Cu/SAC/Co-P flip chip solder joints under rapid thermal fatigue,it is found that Cu atoms segregate in different degrees at the Co-P side interface.On the interface side of Co-5%P,the formation of thicker(Cu,Co)₆Sn₅obviously inhibits the growth of Co Sn₃,and the thickness of interface IMC increase and the morphology tends to be flat.On the Co-13%P interface side,Cu segregates in the front of Co Sn₃ to form irregular bulk(Cu,Co)₆Sn₅,and the thickness distribution of IMC is uneven.On the interface side of Co-20%P,the lamellar Co Sn₃ and the massive(Cu,Co)₆Sn₅ contact and grow alternately.The thickness of IMC at the interface increases obviously and the interior becomes more compact.The evolution law of microcracks shows that the hot crack resistance sensitivity of Co-P side interface solder joint is significantly higher than that of Cu side solder joint,and the cracks occur preferentially on the side of Cu substrate.In the study of Co-P/SAC/Co-P flip chip solder joints under rapid thermal fatigue,it was found that the thickness of IMC on both sides of Co-5%P/SAC/Co-5%P solder joints increased gradually with the increase of cycle time,and the morphology was dense layered Co Sn₃ IMC.With the formation of(Cu,Co)₆Sn₅ phase,the tile like Co Sn₃ on both sides of Co-13%P/SAC/Co-13%P solder joint began to peel off from the interface and dissolve into the solder.At the end of rapid thermal fatigue,the morphology of Co Sn₃ at the interface still did not reach the steady structure,and the thickness of IMC at the interface first increased and then decreased.The evolution of microcracks shows that the joint of Co-13%P/SAC/Co-13%P flip chip structure has an obvious inhibition effect on the thermal fatigue crack growth,and the Co-13%P UBM material system has excellent thermal crack resistance sensitivity under rapid thermal fatigue loading.The results of shear strength test after rapid thermal fatigue loading show that SAC/Co-13%P BGA Solder joint has the best performance,and the shear strength only decreases by10.98MPa to 51.97MPa after loading.The failure mode is ductile brittle mixed fracture dominated by toughness.Co-P UBM as interconnect substrate significantly improves the thermal fatigue reliability of solder joints,which provides an important theoretical basis for solving the reliability research of solder joints in long-term service.