Study On The Interfacial Evolution Of SAC305 Micro Solder Joints Based On The Diffusion Of Graphene Barrier Layer

With the development of lead-free solder in the microelectronic industry,Sn-Ag-Cu?SAC?solder had got wide attention.SAC305 solder was considered as the best substitute material for SnPb solder and had been widely used.Although SAC305 solder obtained promising wettability and mechanical property,the coarsening of IMC layer at the interface between solder and substrates was considered as one of the key factors that lead to the deterioration of the reliability of solder joints.Therefore,the improvement of IMC layer in the solder joints played an important role in the reliability of packaging materials.In this work,the Ni elements were added into the SAC305 solder alloy by melting method,and promoted the formation of solder joints on Cu,H-Cu and G-Cu substrates,the evolution of IMC layers and mechanical property of the solder bulks in the solder joints were investigated.The solderability of SAC305 solder in the SAC305-xNi/Cu,SAC305-Ni/H-Cu?SAC305-Ni/G-Cu solder joints were studied.The addition of Ni elements in the solder alloy affected the wettability of solder joint,the wettability of solder joints on the three substrates were analyzed.Experimental results indicated that as the content of Ni increase,the wettability of micro solder joints on Cu,H-Cu and G-Cu substrates shown a trend of first upward and descend subsequently.The wettability of solder on G-Cu substrate obviously higher than that on Cu and H-Cu substrates.The added Ni elements in the solder alloy and the type of substrates affected the microstructure of solder bulks on the three substrates.The grain size of?-Sn in the SAC305-Ni/G-Cu solder joints was smaller than that on Cu and H-Cu substrates,this phenomenon indicated that the graphene layer had an influence on the solder bulks.Besides,the addition of Ni aggravated the above influence on?-Sn.Compared with the microstructure of solder bulks on Cu and H-Cu substrates,the amount of?-Sn grains significantly increases and the area of eutectic phase decreases.The addition of Ni element in the solder alloy and the type of substrates produced some impact on the morphology and evolution of interfacial IMC layer.The addition of Ni promoted the formation of?Cu,Ni?₆Sn₅ phases,the size of Cu₆Sn₅ grains was larger than that of?Cu,Ni?₆Sn₅ grains.Therefore,As the concentration of Ni ranges from 0 to 0.2 wt%,the thickness of IMC layer on the Cu,H-Cu and G-Cu substrates shown a trend of first ascend and descend subsequently.The IMC layers on the G–Cu have thinner thickness than that on the Cu and H-Cu substrate with the content of Ni varied from 0 to 0.2 wt%.The influence of Ni elements and type of substrates on hardness of the solder bulks of SAC305-Ni on the Cu,H-Cu and G-Cu substrates were investigated.Experimental results indicate that the addition of Ni elements in the solder alloy has limited effect on the hardness of the solder bulks in the SAC305-Ni/Cu and SAC305-Ni/H-Cu solder joints.However,the addition of Ni in the solder alloys led to a decrease trend of the hardness of the solder bulks on G-Cu substrate.The hardness of SAC305-Ni solder bulks on G–Cu was lower than that on Cu and H-Cu substrates.The morphology of interfacial IMC layers,the microstructure of the solder bulks and the hardness of the solder bulks after isothermal aging were analyzed.Due to the diffusion of Cu and Sn atoms at the interface between solders and substrates during aging process.Thus,the total thickness of interfacial IMC layer on the Cu,H-Cu and G-Cu substrates increased with the duration of aging time.For the microstructure of the solder bulks on the Cu,H-Cu and G-Cu substrates after isothermal aging,the evolution of microstructure in the SAC305-Ni/Cu?SAC305-Ni/H-Cu and SAC305-Ni/G-Cu solder joints shown the same phenomenon.As the increase of aging time,the amount of?-Sn rose but the eutectic area declined in the SAC305-Ni/Cu,SAC305-Ni/H-Cu and SAC305-Ni/G-Cu solder joints.However,the number of IMC phases in the solder bulks increased,which was the result of IMC grain diffusion at the interface.Therefore,the hardness of solder bulks on the three substrates rose with the extension of aging time.In addition,the hardness of the solder bulks on G-Cu substrate was smallest than that on Cu and H-Cu substrates.