Study On Interface Structure And Mechanical Property Of Cu/Ni(P) Bi-layer Solder Joint

At present,the research on reliability of lead-free solder joint in electronic components has become one of the important content on electronic packaging,especially the interface morphology and structure on solder joints can affect the solder joint performance greatly,making this part more attention.The SnAgCu system lead-free solder development results have been applied in many fields.But there still has the problem about the reliability of solder deserves further study in the application.The wide application lead-free solder of Sn-3Ag-0.5Cu?SAC305?was used in the experiment.To study the interface structure and morphology changes of SAC305/Cu solder joints in different solid state aging temperatures?especially at high temperature?,the three different solid state aging temperatures of 120 ^oC,180 ^o C and 200 ^oC were applied.The results shows that only scallop-like Cu₆Sn₅ IMC phase could be found in the interfacial layer after soldering,and Cu₃Sn phase appeared at after aging treatment.The initial scallop-like IMC transformed to a more planar type layer at low and intermediate aging temperature,but turned to hump at high aging temperature.High temperature accelerated the solid-state reaction.The formation of interfacial IMC morphology is mainly dominated by the Cu atom heterogeneous nucleated in the IMC surface.The thickness of total IMC,Cu₆Sn₅ and Cu₃Sn increased linearly with square root of aging time,and the diffusion coefficient increased with increasing aging temperature.The activation energies of the total Cu-Sn,Cu₆Sn₅ and Cu₃Sn intermetallic were 115.2,122 and 98 kJ/mol,respectively.To study the effects of Cu/Ni?P?double barrier coating between the Cu and SAC305 solder,the growth behavior and morphology of IMCs were observed at different aging temperatures.The experimental results showed that double barrier layer still has good blocking effect in the temperature of 150^oC even only 1.19?m coating existed in the interface.With increasing temperature and time,the thickness of the double barrier coating thinned and depleted.In the temperature of 210 ^oC which close to the SAC305 melting point,the inhibitory effect of thin coating disappeared quickly and no longer significantly at solid-state aging,which is related to the thickness of the coating.The new compound?Cu,Ni?₆Sn₅ formed at the interface.Compared with the pure Cu substrate,double coating has obvious inhibitory effect on the IMCs growth.The shear test were applied for the three different substrate?pure copper plate,Ni?P?plate and double coating?solder joint performance evaluation.The experimental results at shear rate of 1mm/min showed as follows.At the start of aging process,the shear strength of pure copper substrate is increased by the pinning effect caused by the growth of IMC.With the increase of aging time,the strength of IMC decreased due to the overgrowth of brittle IMC.The mechanical performance of Ni?P?coated substrate decreased with the increase of aging time.This is due to the coating transformation inside the solder joint interface and the brittle Ni-Sn phase appeared.With the increase of aging time,the thermal expansion coefficient between substrate and IMC does not match,and the thin needle IMC tend to be stress concentration.The brittleness of IMC has a major effect on the shear tension.The mechanical properties of the double coating are relatively smooth at shear tested.As the double barrier layer inhabited the diffusion of atoms,the growth of IMC at the interface was slow and the thickness was near.The interface fracture position appears in the middle of IMC.Regardless of the aging time,the IMC shear strength in the interface of the double coating is stable at about 21 MPa.The shear strength of double coating solder joint is little higher than single coating solder joint after long solid-state aging time.