Effect of CeO2 particles on the high phosphorus electroless Ni layer
Electroless Ni (EN) technology is widely used in electronic package field and the high phosphorus composite EN technology was studied. In this paper, we discussed the influence of nano-CeO2 and micro-CeO2 particles with different amounts when they were added in high phosphorus content Ni-P composite coating. The microstructure and crystal structure of the coating were observed by scanning electron microscope (SEM) and X-ray diffraction analysis (XRD) respectively. The results showed that whether nano-CeO2 or micro-CeO2, both refined the grain, increased the specific surface area, however the micro-CeO2 particles made more obvious effect. As the XRD result showed, the peak gradually become gentle, the coating turned into amorphous which may cause by the CeO2 particles absorbed in the grain boundary and crystal defects. The results indicated the CeO2 deposited with the coating very well. Finally, the corrosion resistance of the coating was tested with the method of electrochemical impedance (EIS) and linear polarization. The results were unified. When the dosage is 5g/L, the corrosion resistance was the best. However, lower corrosion resistance was got when excessive CeO2 particles were added which may affect by the catalytic property.
Thermal conductive properties of Ni–P electroless plated SiCp/Al composite electronic packaging material
Abstract Electroless plated SiC p /Al composites with a high thermal conductivity are required for electronic packaging application. In this paper, in-plane thermal conductive properties of SiC p /Al composites with and without electroless plated Ni–P coatings are compared, and influence of various characteristics of Ni–P coatings are investigated. It is found that in addition to thickness of the coatings, phosphorus concentration and microstructure of the plated layers also influence the thermal conductive properties of plated composites. Based on the results, it is suggested that a low phosphorus concentration and a properly tailored crystalline microstructure of the Ni–P coatings, together with a reasonable choice of coating thickness, may contribute to optimization of thermal conductive properties of the composite material.
ENIG Corrosion Induced by Second-Phase Precipitation
Materials analysis of a flip-chip package lot with solder bump interconnect failures revealed a new mechanism for corrosion of electroless nickel immersion gold surface finish. Detailed scanning and transmission electron microscopy (SEM and TEM) in conjunction with focused ion beam microscopy and electron dispersion analysis of the unsoldered ball grid array substrate pads on packages that exhibited flip-chip solder bump interconnect failures revealed an unusual and subtle defect in the original Ni(P) layer, which was ultimately responsible for flip-chip joint failure. Detailed TEM analysis of the defect regions showed that they consisted of Ni(P) particles of slightly different composition than the bulk Ni(P) layer. Microstructure changes around these incorporated particles indicated that the second-phase particles were deposited from the plating bath during the Ni(P) growth stage. The second-phase particles provided additional surface area for nucleation and growth of Ni(P). Ultimately, a low-density boundary region in the growing Ni(P) layer formed where the particle-induced growth front and the planar Ni(P) film growth front intersected. This low-density interface eventually terminated at the surface of the Ni(P) layer. In addition the growth from the second-phase particle created localized surface topology that was different than that of the surrounding Ni(P) layer. The low-density interfaces as well as the surface topology led to enhanced corrosion of the Ni(P) layer when exposed to the immersion gold plating process. In some cases the corrosion was severe enough to create voids in the Ni(P) layer. The exposed, oxidized Ni(P) surfaces in and around these enhanced corrosion regions did not wet when exposed to solder. This led to degradation in the strength of the solder joint and subsequent solder interconnect failure.