J. D. Guo

Effects of Zn addition on electromigration behavior of Sn–1Ag–0.5Cu solder interconnect

Effects of electromigration on microstructure and tensile property were studied in the Sn–1Ag–0.5Cu and Sn–1Ag–0.5Cu–1Zn solder interconnects. While the polarity effect and strength reduction from electromigration occurred in the Sn–1Ag–0.5Cu solder interconnects, they were suppressed by the Zn addition in the Sn–1Ag–0.5Cu–1Zn solder interconnects. Such a strong effect of Zn was explained by the strong binding of Zn with Cu, which prevented the dissolution of the IMC at the cathode, and by the reverse migration of the Zn elements, which counteracted the increase in the vacancy concentration so that the strength reduction was successfully inhibited.

Inhibition of Electromigration in Eutectic SnBi Solder Interconnect by Plastic Prestraining

Plastic prestraining was applied to a solder interconnect to introduce internal defects such as dislocations in order to investigate the interaction of dislocations with electromigration damage. Above a critical prestrain, Bi interfacial segregation to the anode, a clear indication of electromigration damage in SnBi solder interconnect, was effectively prevented. Such an inhibiting effect is apparently contrary to the common notion that dislocations often act as fast diffusion paths. It is suggested that the dislocations introduced by plastic prestraining acted as sinks for vacancies in the early stage of the electromigration process, but as the vacancies accumulated at the dislocations, climb of those dislocations prompted recovery of the deformed samples under current stressing, greatly decreasing the density of dislocation and vacancy in the solder, leading to slower diffusion of Bi atoms.

A new isotope of protactinium:239Pa

A new nuclide239Pa was produced by 50MeV/u18O bombardment of uranium. A radiochemical separation method was employed for preparing sources of239Pa. The protactinium isotope239Pa has been identified for the first time by the results observed from the decay of the239Pa and its daughter239U. The half-life of239Pa has been determined to be 106 ±30min.

Decay study of20Na and its beta-delayed16O recoiling

The decay of20Na of astrophysical reactions has been studied deeply via20Ne(p, n)20Na reaction. A new β-delayed α decay with α energy of 5 896 ± 6 keV and relative intensity of 0.002 4 ± 0. 000 3 was discovered. At the same time the16O recoiling in β+-delayed α decay of20Na was observed in experiment for the first time. From these, it is inferred that a β-delayed low energy α decay of20Na with energy of ∼780 keV and relative intensity of ∼1.4 was mixed in16O recoiling. In16O recoiling and the low energy α decay, the energy loss for low energy charged particles through matter was discussed in detail. At last, two methods for discriminating the β-delayed low energy α decay of20Na were proposed.

Failure behavior of flip chip solder joint under coupling condition of thermal cycling and electrical current

In this work, the failure behavior of a commercial chip size packaging (CSP) with flip chip solder joint was investigated under the coupling condition of thermal cycling and electrical current. The damage behavior of solder joint was real-time monitored through the electrical resistance response. The microstructure evolution under the coupling condition were observed. The failure was classified as three modes, i.e., the cracking within solder on the PCB side (mode I), the cracking along the solder/IMC interface (mode II) and the detachment between the solder and chip due to the complete dissolving of Cu UBM layer (mode III). At low current density the mode I accounted for a large percentage while the mode II and mode III accounted for a large percentage at high current density. Based on the Weibull distribution of failure life, it was found that the mean time to failure sharply decreased with the increasing current density. A lifetime prediction model was constructed for the reliability test under coupling condition of thermal cycling and electrical current.

Production and identification of new neutron-deficient isotope235Am in region of transuranium

A new transuranium neutron-deficient isotope235Am was produced by 35 MeV proton to bombard the rare radioactive238Pu target. The products were transported and collected by the He-jet system. The Am isotopes were separated and purified by radiochemistry method and the y-ray, X-ray and y-X(y) coincidence of the samples was measured. The synthesis of235Am was definitely identified. Its measured half-life is (15±5) min.