| With further increase of the flip chip package density, the corresponding feature sizes of micro-bumps gradually reduced to about 100 ?m, the interfacial reaction and reliability problems of micro-scale solder joints will become more complex and need for detailed study. Now studies on high-Pb micro-bump welding is rather less, which can't provide theoretical guidance for practical technology choice. This paper focused on the interfacial reaction and mechanical properties of FC-CCGA1 144 devices 130 ?m micro-bumps, which include interfacial microstructure, grain morphology, shear strength and shear fracture mode of solder joints. By the above experiment results to optimize components and reflow process of flip chip micro-bumps; In addition, the thermal cycle stress-strain of flip chip micro-bumps were also evaluated.The main contents and results were as follows:1. Study the interfacial reaction and mechanical properties of 95Pb-5Sn,90Pb-10Sn and 85Pb-15Sn (in wt.%) flip chip solder bumps with the Ni and Ni-B metallizations after single and three times reflows show that the interfacial reaction rate of 95Pb-5Sn and 90Pb-10Sn solders with Ni BUM were much lower, while the interfacial reaction rate of 85Pb-15Sn solder with Ni BUM was significantly increased, with the grain size significantly coarsening. The interfacial reaction kinetics of Ni and Ni-B metallizations with three solders indicates that the interfacial reaction rate of Ni-B is significantly lower than that of Ni after single and three times reflows, and the interfacial reaction rate of 85Pb-15Sn/Ni UBM joint is twice that of 85Pb-15Sn/Ni-B joint. By calculating Sn content in the three solder bumps, it indicates the decline percentage of Sn content in 90Pb-10Sn bumps was lower than that of 95Pb-5Sn and 85Pb-15Sn. Shear fracture morphology shows all solder joints are ductile fracture, and with the Sn content increasing, the shear strength increases but the shear distance is slightly reduced. By the comparison of interfacial reaction, grain size, UBM consumption, shear performance, considering the 90Pb-10Sn solder has the best service performance.2. Study the the interfacial reaction and mechanical properties of 90Pb-10Sn solder bumps with Ni and Ni-B metallizations under different reflow time show that both Ni and Ni-B interfaces formed Ni3Sn4 IMC, and the average grain size of Ni3Sn4 IMC increased from 0.8 ?m to 1.2 ?m when the reflow time changed from 50 s to 150 s; Ni UBM consume more excessive between 90Pb-10Sn\Ni solder joint after 150s reflow time, resulting in decreasing of pad strength, and the failure mode of joint behaves fracture along the pad. The shear strength of 90Pb-10Sn/Ni-B solder joints were approximately 320 mN after 50-70 s reflow time, while it decreased to 250 mN after the reflow time increased to 100-150 s, namely the shear strength decreased by 20%. By the comparison of interfacial reaction, grain size, UBM consumption, shear performance, considering 50-70s reflow time is more appropriate process parameters for 90Pb-10Sn solder bumps.3. Study the thermal cycling stress and strain of micro-bumps show that the solder joints strain with underfill were reduced by approximately 20-30 times compared with solder joints without underfill. By comparing with different models of underfills, it indicates the strain level decreased when the difference of thermal expansion coefficients between underfill and solder were much closer. The strain levels decline when the bump size increased from 80 ?m to 130 ?m. For the initial diameter of 130 ?m solder bumps, the lower the bump height, the greater of joint strain during thermal cycling. By comparing the stress and strain of solder joints under different temperature curves, it indicates the stress level of solder joints increase with rapid temperature change. |
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