Effects of MnSO₄ on microstructure and electrical resistance properties of electroless Ni−P thin-films and its application in embedded resistor inside PCB

Abstract

Purpose -Nickel phosphorus (NiZP) thin-films have been electrolessly deposited in an acid-plating bath with the addition of manganese sulfate monohydrate (MSM) to achieve higher resistance for the application of embedded resistor with value beyond 10 KV. As this material is being used for fabricating embedded resistors under the addition of MSM, its resistance properties including effects of MSM concentration and plating time on resistances, temperature coefficient of resistance (TCR), and resistance tolerance of embedded resistor were investigated. The paper aims to discuss these issues. Design/methodology/approach -The structure of fabricated NiZP film was detected by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The properties of substrate, including the surface morphologies, glass transition process and boundary of copper pad and substrate surface, were performed by SEM, dynamic mechanical analysis and optical microscope, respectively. The resistance tolerances of embedded resistors were elaborated from the cases of NiZP thin-film resistance tolerance and the size effects of resistors, respectively. Findings -The fabricated film was found to be constructed with numerous NiZP amorphous nanoparticles, which was believed to be the reason of increasing thin-film resistance. The NiZP thin-films presented over one magnitude order of resistance increasing in the case of MSM concentration varied from 0 to 40 g/L. For the case of TCRs, NiZP thin-films deposited with 20 g/L MSM exhibited low TCRs of within^100 ppm/8C Before TR at temperature elevating from 40 to 1608C, indicating that this NiZP thin-film belongs to the constant TCR materials according to the military standard. For the tolerance of embedded resistor, the tolerance contributed by NiZP thin-film was obtained to be 9.8 percent, whereas the geometry tolerances were in the range of 0-20 percent according to the geometries of embedded resistor. Originality/value -For NiZP thin-film without MSM, its low resistance with around 100 ohm/sq. limit the values of resistor few KV and restricted its widespread application of embedded resistor with higher resistance beyond 10 KV. The authors introduced MnSO 4 in NiZP electroless plating process to improve the low resistance of NiZP thin-film. The resistance was increased over one order of magnitude after added with 40 g/L MnSO 4 . Due to the specific structure, as this material is being used for fabricating embedded resistors, the electrical properties and its application properties to verify its appliance in embedded resistor were systematically investigated by means of SEM, TEM, XRD characterizations, TCRs, resistance tolerance analysis, respectively.

Improved uniformity of Ni/Au coating on circuits by electroless plating

“…In addition, electra-deposition Ni/Au coating exhibits the laminated growth mode. Its inter-crystalline groove could be easily soaked by the electrolyte which results in lateral corrosion, polluting and shortening the life of the gold-plated electrolyte [9]. In severe cases, Cu line would be corroded, leading to decrease in line accuracy and the adhesion strength of the coatings.…”