Lai Wang

The liquid structure of Sn-based lead-free solders and the correlative effect in liquid-solid interfacial reaction

Two lead-free solder alloys, Sn-0.7Cu and Sn-2Cu (wt.%), have been examined using X-ray diffraction method. The liquid structure of Sn-0.7Cu is similar to that of pure Sn. A pre-peak has been found in the low Q part on the structure factor S(Q) for Sn-2Cu tested under 260°C, but it disappeared finally when the testing temperature reached 400°C. The interfacial reactions between liquid solders and Cu substrates at 260°C were also studied. The results show that the IMC layer at Sn-2Cu/Cu joint is thicker than that at Sn-0.7Cu/Cu interface. The correlative effect of liquid structure on phase evolution in the solder joints are analyzed and discussed.

The effect of Bi on the IMC growth in Sn-3Ag-0.5Cu solder interface during aging process

The solder materials used to make the solder joints for this study are: eutectic Sn-3Ag-0.5Cu solder; Sn-3Ag-0.5Cu-1Bi solder; and Sn-3Ag-0.5Cu-3Bi quaternary solder. In order to study the microstructure evolution and the IMC growth kinetics, the solder joints were aged isothermally in a resistance oven at 150/spl plusmn/5/spl deg/C with different periods of 0, 50, 100, 250, 500, and 1000 hours. The result show that: the morphology of IMC changes from scallop-like to planar in the aging process; the mean thickness of IMC layer solder joints is found to increase linearly with the square root of aging time, namely the growth of IMC is controlled by atom diffusion; the IMC growth rate decreased as Bi content increased. For the solders discussed above, the comparative IMC growth rate sequence from fast to slow is Sn-3Ag-0.5Cu > Sn-3Ag-0.5Cu-1Bi > Sn-3g-0.5Cu-3Bi.

The Evaluation of Sn-58Bi Composite Solder Mixed with Y2O3

With the development of surface mount technology, solders are required for applications that require high reliability and dimensional stability. Composite solders reinforced with particles in a conventional solder alloy, is an attractive and potential method. This study presents series results on the binary eutectic Sn-Bi composite solders reinforced with Y₂O₃ particles from 0 to 3%. With this process, the reinforcement particles are well dispersed in the solder matrix and depress the growth of IMC layer. The gray impurities on the surface of the Sn-Bi solder cap are estimated to be Bi₂O₃ by XRD. With the increase of Y₂O ₃ content, the surface of the solder cap gets brighter and the number of fine particles mainly made up of Y₂O₃ and Bi₂O₃ around the solder joints increases. The wetting properties and the shear strengths of solders are improved by the addition of Y₂O₃

Liquid-state and solid-state interfacial reactions between Sn-Ag-Cu-Fe composite solders and Cu substrate

The growth kinetics and morphology of the interfacial intermetallic compound (IMC) between Sn–3Ag–0.5Cu–xFe (xxa0=xa00, 0.5 wt%, 1 wt%) composite solders and Cu substrate were investigated in the present work. The Sn–Ag–Cu–Fe/Cu solder joint were prepared by reflowing for various durations at 250xa0°C and then aged at 150xa0°C. During soldering process, Fe particles quickly deposited in the vicinity of IMC, resulting in the formation of Fe-rich area. Isothermal equation of chemical reaction and phase diagrams were used to explain the effect of Fe on the growth kinetics of IMC during liquid-state interfacial reaction. It was shown that Fe could effectively retard the growth of interfacial Cu6Sn5 and Cu3Sn layers during liquid-state reaction and reduce the size of Cu6Sn5 grains. Small cracks were observed in the Cu6Sn5 grains after reflowing for 2xa0min while they were found in the other composite solders reflowing for about 30xa0min. The Fe tended to suppress the growth of the Cu3Sn layer during solid-state aging. However, the total thickness of IMCs (Cu6Sn5xa0+xa0Cu3Sn) for the composite solders with Fe particles was similar to that for SnAgCu without Fe particles.

Effect of Fe addition to Sn-3Ag-0.5Cu solder on interfacial reactions during aging

The growth kinetics and morphology of the interfacial intermetallic compound (IMC) Cu₆Sn₅ between Sn-3Ag-0.5Cu-xFe (x= 0, 0.5wt.%, 1wt.%) composite solders and Cu substrate during aging were investigated in the present work. The Sn-Ag-Cu-Fe/Cu solder joint were prepared by reflowing for various durations at 250°C and then aged at 150°C. The Fe element tended to suppress the growth of the Cu₃Sn layer during solid-state aging. However, the total thickness of IMCs (Cu₆Sn₅ + Cu₃Sn) for the composite solders with Fe particles was similar to that for SnAgCu without Fe particles.

Effect of Bi on the kinetics of intermetallics growth in Sn-3Ag-0.5Cu/Cu solder joint

Three lead-free solder alloys, Sn-3Ag-0.5Cu, Sn-3Ag-0.5Cu-1Bi and Sn-3Ag-0.5Cu-3Bi, were used in the current experiments to investigated the microstructural evolution as well as the kinetics of intermetallic compound (IMC) layer growth. The experimental results indicated that the thickness of Cu6Sn5 intermetallic layer at the solder/Cu interface increases with aging temperature, while the growth rate of IMC in Sn-3Ag-0.5Cu-3Bi/Cu joints is slower than that in Sn-3Ag-0.5Cu-1Bi/Cu joints and Sn-Ag-Cu solder joints. The effect of Bi element is attributed to the accumulation of Bi near the joint and the enhancement of the activation energy by the addition of Bi