Electroplated indium bump arrays and the bonding reliability

A novel electroplating indium bumping process is described,as a result of which indium bump arrays with a pitch of 100μm and a diameter of 40μm were successfully prepared.UBM（under bump metallization） for indium bumping was investigated with an XRD technique.The experimental results indicate that Ti/Pt（300（？）/200（？）） has an excellent barrier effect both at room temperature and at 200℃.The bonding reliability of the indium bumps was evaluated by a shear test.Results show that the shear strength of the indium bump significantly increases after the first reflow and then changes slowly with increasing reflow times.Such a phenomenon may be caused by the change in textures of the indium after reflow.The corresponding flip-chip process is also discussed in this paper.

Mechanism of improved electromigration reliability using Fe-Ni UBM in wafer level package

Fe-Ni films with compositions of 73 wt% of Ni and 45 wt% of Ni were used as under bump metallization （UBM） in wafer level chip scale package, and their reliability was evaluated through electromigration （EM） test compared with commercial Cu UBM. For Sn3.SAg0.7Cu（SAC）]Cu solder joints, voids had initiated at Cu cathode after 300 h and typical failures of depletion of Cu cathode and cracks were detected after 1000 h EM. While the SAC]Fe-Ni solder joints kept at a perfect condition without any failures after 1000 h EM. Moreover, the characteristic lifetime calculated by Weibull analysis for Fe-73Ni UBM （2121 h）, Fe-45Ni UBM （2340 h） were both over three folds to Cu UBM＇s （698 h）. The failure modes for Fe-Ni solder joints varied with the different growth behavior of intermetallic compounds （IMCs）, which can all be classified as the crack at the cathodic interface between solder and outer IMC layer. The atomic fluxes concerned cathode dissolution and crack initiation were analyzed. When Fe-Ni UBM was added, cathode dissolution was suppressed due to the low diffusivity of IMCs and opposite transferring direction to electron flow of Fe atoms. The smaller EM flux within solder material led a smaller vacancy flux in Fe-Ni solder joints, which can explain the delay of solder voids and cracks as well as the much longer lifetime under EM.

Effect of Fe Content on the Interfacial Reliability of SnAgCu/Fe—Ni Solder Joints

Fe-Ni films with compositions of Fe-75Ni, Fe-50Ni, and Fe-30Ni were used as under bump metallization （UBM） to evaluate the interracial reliability of SnAgCu/Fe-Ni solder joints through ball shear test, high temperature storage, and temperature cycling. The shear strengths for Fe-75Ni, Fe-5ONi, and Fe-3ONi solder joints after reflow were 42.57, 53.94 and 53.98 MPa, respectively, which were all satisfied the requirement of industrialization （〉34.3 MPa）. High temperature storage was conducted at 150, 175 and 200 ℃. It was found that higher Fe content in Fe-Ni layer had the ability to inhibit the mutual diffusion at interface region below 150 ℃, and the growth speed of intermetallic compound （IMC） decreased with increasing Fe concentration. When stored at 200 ℃, the IMC thickness reached a limit for all three films after 4 days, and some cracks occurred at the interface between IMC and Fe-Ni layer. The activation energies for the growth of FeSn2 on Fe-30Ni, Fe-5ONi, and Fe-75Ni films were calculated as 246, 185, and 81 kJ/mol, respectively. Temperature cycling tests revealed that SnAgCu/Fe-5ONi solder joint had the lowest failure rate （less than 10%）, and had the best interfacial reliability among three compositions.