The electromigration behavior of microbumps is inevitably altered under bidirectional currents. Herein, based on a designed test system, the effect of current direction and time proportion of forward current is investigated on Cu Pillar/Ni/Sn-1.8 Ag/Cu microbumps. Under thermo-electric stressing, microbumps are found to be susceptible to complete alloying to Cu6Sn5 and Cu3Sn. As a Ni layer prevents the contact of the Cu pillar with the solder, Sn atoms mainly react with the Cu pad, and the growth of Cu3Sn is concentrated on the Cu pad sides. With direct current densities of 3.5 × 104 A/cm2 at 125 °C, the dissolution of a Ni layer on the cathode leads to a direct contact reaction between the Cu pillar and the solder, and the consumption of the Cu pillar and the Cu pad shows an obvious polarity difference. However, with a bidirectional current, there is a canceling effect of an atomic electromigration flux. With current densities of 2.5 × 104 A/cm2 at 125 °C, as the time proportion of the forward current approaches 50%, a polarity structural evolution will be hard to detect, and the influence of the chemical flux on Cu-Sn compounds will be more obvious. The mechanical properties of Cu/Sn3.0Ag0.5Cu/Cu are analyzed at 125 °C with direct and bidirectional currents of 1.0 × 104 A/cm2. Compared with high-temperature stressing, the coupled direct currents significantly reduced the mechanical strength of the interconnects, and the Cu-Sn compound layers on the cathode became the vulnerable spot. While under bidirectional currents, as the canceling effect of the electromigration flux intensifies, the interconnect shear strength gradually increases, and the fracture location is no longer concentrated on the cathode sides.
Modern electronics is characterised by the increasing level of integration in printed
circuit board (PCB) technology and the reduced insulation spacing between adjacent
conductors. Surface insulation resistance (SIR) measurement has often been used
alone to determine the cleanliness of PCB assembly; however, when proper SIR
measurement is used in conjunction with surface leakage current (SLC) measurement,
the result can reveal the dynamic nature of surface electrochemical migration (SECM)
processes at the microscopic level, and the effect of such processes on product quality and
reliability. This paper presents a newly developed measurement methodology, which measures
SLC per square unit area at a sampling rate that is orders of magnitude higher than that of
conventional SIR measurement methods. It is aimed to capture the transient surge of SLC which
is detrimental to the functionality of product.
The ESD characteristic of SOl NMOSFET with different gate structures was studied. It was indicated that the ESD robustness ability was the strongest in gate around source (GAS) structure and was the weakest in enclosed gate structure in SOl NMOSFET. This was probably related to interested areas and current density.
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