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采用直径范围为200—600μm的Sn3.0Ag0.5Cu无铅钎料球在Cu焊盘上制作热风重熔焊点,将重熔焊点在150℃下进行老化,并对重熔和老化焊点进行剪切测试.结果表明:重熔和老化后焊点的剪切强度都随体积的增大而减小,表现出显著的体积效应.SEM断面观察显示:较小体积焊点剪切断裂发生在钎料块体内部,表现出较好韧性;较大体积焊点则发生在近焊盘的界面处,呈现脆性断裂特征.焊盘界面处和钎料内部微观组织SEM观察表明:小体积焊点内部Ag_3Sn化合物以小颗粒状弥散分布,起到强化作用;而大体积焊点内部Ag_3Sn化合物为树枝网状分布,表现出硬脆性.金属间化合物(如Ag_3Sn和Cu_6Sn_5)的形貌和分布对焊点的断裂行为有显著的影响,是焊点剪切断裂行为体积效应的内在原因.
A hot-air reflow spot was fabricated on a Cu pad using a Sn3.0Ag0.5Cu lead-free solder ball with a diameter in the range of 200-600 μm. The reflow spot was aged at 150 ° C., and the reflow and aged solder joints The results show that the shear strength of the solder joint after remelting and aging decreases with the increase of volume, and shows a significant volume effect.SEM cross-section observation shows that the shear fracture of the solder joint with smaller volume occurs In the bulk of the brazing filler metal, it shows better ductility; the larger volume of the solder joint occurs at the interface near the pad, showing the brittle fracture characteristics.The SEM observation of the microstructure at the pad interface and the brazing filler metal shows that: Ag_3Sn compounds dispersed in small particles play a strengthening role, while Ag_3Sn compounds in large-volume solder joints showed a net-like distribution with hard and brittle properties.The morphologies and distribution of intermetallic compounds (such as Ag_3Sn and Cu_6Sn_5) The fracture behavior of the solder joint has a significant effect, which is the intrinsic reason for the volume effect of the shear fracture behavior of the solder joint.