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.
Qualitative electroless Ni/Au plating considerations for the solder mask on top of sequential build-up layers
Advanced printed circuit boards (PCBs) with sequential build-up (SBU) layers require alternating dielectric and copper layers on top of a core substrate. This can be achieved by lamination of resin coated copper (RCC) or by coating of dielectric polymers followed by copper deposition. The plating of electroless Ni/Au used as a solderability preservative on top of sequential build-up layers is investigated. For this application a solder mask polymer has to be applied in order to separate solder pads. Experiments showed that on parts of the underlying build-up layer exposed to the electroless Ni plating solution electroless Ni can grow. This overplating is caused by the remains of colloidal Pd/Sn catalyst on top of the build-up layer from preceding electroless Cu deposition. At very small features skipping of the plating can also take place. The overplating and skipping phenomena are influenced by a number of parameters, such as the temperature, the concentration of the stabilizer and pH. The dimensions of features on the board and the thickness of the solder-mask polymer also influence skipping. Based on qualitative analyses of the skipping and overplating phenomena rules of thumb for the solder mask design based on the plating conditions are proposed.
A corrosion couple experiment reproducing the black pad phenomenon found after the electroless nickel immersion gold process
The “black pad” phenomenon, which rarely occurs in electrolessly plated nickel–phosphorous (Ni–P) films, was reproduced. This work reports that nodular variation of the P content induces potential differences large enough to drive galvanic corrosion when the film is exposed to an electrolyte containing gold cyanide. Subsequent corrosion couple experiments using Ni–P films with different P contents demonstrated that preferential corrosion occurred at the low P side, and the propensity of forming black pad increased with the difference in P content (ΔP).