In this paper, the discoloration of the solder after the vacuum sintering of the power chip is analyzed. The morphology and composition of the discoloration area were characterized and analyzed by the metallographic microscope, SEM, EDS and XPS, and the discoloration mechanism was studied. The analysis results show that the main components of the color-changing solder are C, O, Pb, Sn, Ni, Ag, and Au, which are the normal components of the solder after vacuum sintering. The reason for color-changing is the oxidation of the Sn element, and the different thickness of oxide shows different colors. The discoloration solder was treated with formic acid, and the solder returned to bright silver-white. The test further confirmed that the discoloration was caused by metal oxidation. The problem of solder discoloration is solved by optimizing the process to reduce the sintering time and vacuum defoaming time.

The effect of loading of stainless steel fiber (SSF) and temperature on electrical resistivity of SSF/PA6 conductive polymer composites was investigated in this paper. The distribution of fibers in the composites was observed by means of scanning electron microscopy（SEM）. The experimental results show that the resistivity decreases closely along with the increase of SSF loading from 0 to 12 Wt. % and temperature from 20 to 200°C. It is shown by SEM that the fibers are dispersed homogeneously in the polyamide-6 matrix.

The interfacial fracture strength in polymer blends is investigated in this study. The constitutive relations of polymeric matrix and inclusions are both approximately described by linear viscoelastic models. It is assumed that the interfacial de-boding between inclusions and matrix is dominantly induced by the hydrostatic component of remote stress. Based on the assumption, the interfacial de-bonding of a viscoelastic inclusion embedded in an infinite polymeric matrix is analyzed. It is found that the size of inclusion will strongly affect the magnitude of critical stress, and the effect of Poisson’s ratio on the de-bonding is so small that can be ignored.

In order to detect the variation of electro-conductive property of polymeric composite under impact loading, a modified split Hopkinson pressure bar (M-SHPB) is suggested. Such M-SHPB is constructed by designing a new test electrocircuit, and connecting it to the specimen and oscillograph. On the other hand, a copper foil cover is designed and placed on the whole SHPB equipment for avoiding interference of electromagnetic wave existing in the testing environment. By means of M-SHPB, the relation between the resistance and dynamic strain is effectively detected.