Rapid Thermal Shock Behavior Of BGA Solder Joints With Cu(Ni)/Sn-xPb/Cu(Ni)

With the continuous development of microelectronic packaging technology,the integration density of electronic products is getting higher and higher,and the power that its internal solder joints bear is increasing,resulting in a sharp increase in current density and outstanding thermal reliability of solder joints.In addition,since high-lead solder is irreplaceable and continues to be exempted from use,high-lead Sn-Pb solder is still used in the packaging process of many high-reliability electronic products such as aerospace,deep space exploration,medical equipment,and military industries.So,lead solder reliability issues are still quite prominent.In this paper,a self-made rapid thermal shock experimental device is used to simulate the thermo-mechanical reliability of Sn-Pb solder bumps and solder joints in the service environment of high-power devices.The effects of different lead contents and pads on the microstructure,internal cracks,intermetallic compounds(IMC)and mechanical properties of bumps and solder joints under the condition of rapid alternating between cold and heat were studied,and the following conclusions were drawn:(1)Based on the fact that Sn90Pb and Sn95Pb solder had less Sn content than Sn80Pb solder,the thickness of Sn80Pb/Cu bump interface IMC was always significantly larger than Sn90Pb/Cu and Sn95Pb/Cu in the same cycle,and after the interface compound Cu₆Sn₅was converted into two layers of(Cu,Ni)₆Sn₅+Ni₃Sn₄,the total thickness of the Sn80Pb/Ni,Sn90Pb/Ni and Sn95Pb/Ni bump interface IMC was quite different at low impact cycles(0 to 2500),while the total thickness of the IMC on the three bump surfaces was similar at high impact cycles(3500 to 5500).With the increase of the rapid thermal shock cycle,cracks with different widths and depths appeared at the left and right corners of the six bump interfaces of Sn80Pb/Cu,Sn90Pb/Cu,Sn95Pb/Cu,Sn80Pb/Ni,Sn90Pb/Ni,Sn95Pb/Ni.Under the same lead content,the crack propagation resistance of Ni pad bump was better than that of Cu pad bump at low cycle,and vice versa at high cycle.Under the same cycle,the shear strength of Ni pad bumps was higher than that of Cu pad bumps under the same lead content.(2)The IMC of the upper and lower interfaces of Cu/Sn-xPb/Cu solder joints was Cu₆Sn₅,and the IMC of the upper and lower interfaces of Ni/Sn-xPb/Ni solder joints was(Cu,Ni)₆Sn₅+Ni₃Sn₄,and the IMC of the Cu interface on the lower side of the Cu/Sn-xPb/Ni solder joint was(Cu,Ni)₆Sn₅,and the IMC of the Ni interface on the upper side is(Cu,Ni)₆Sn₅+Ni₃Sn₄.With the increase of rapid thermal shock cycle,cracks with different widths and depths appeared at the four corners of the upper and lower interfaces of six solder joints of Cu/Sn80Pb/Cu,Cu/Sn90Pb/Cu,Ni/Sn80Pb/Ni,Ni/Sn90Pb/Ni,Cu/Sn80Pb/Ni,Cu/Sn90Pb/Ni.When the solder was Sn80Pb,the crack growth resistance of different solder joints followed the rule:Cu-Ni>Cu-Cu>Ni-Ni,and under the solder was Sn90Pb,the crack growth resistance of different solder joints also followed the above rule.(3)The fractures of the six original solder joints occurred inside the solder matrix,and the fracture morphology was dominated by dimples,which were ductile fractures.With the rapid thermal shock,the density of the dimples at the fracture of the solder joints decreased,and the large dimples were the main ones.When the solder was Sn80Pb,the tensile strength of the three different solder joints at 0 cycle followed the law of Ni-Ni>Cu-Ni>Cu-Cu,and with the increase of the rapid thermal shock cycle,the maximum decrease of the tensile strength followed the law of Ni-Ni>Cu-Ni>Cu-Cu.When the solder is Sn90Pb,the tensile strength of the three different solder joints at 0 cycle follows the law of Cu-Ni>Cu-Cu>Ni-Ni,and with the increase of the rapid thermal shock cycle,the maximum decrease of the tensile strength followed the law of Cu-Ni>Ni-Ni>Cu-Cu.