Co-Ni Electroless Composite Plating of Nanometer-Leveled Diamond Particles on Micrometer-Leveled Plastic Balls and the Application of Thus Prepared Devices to Various Electronics Processes
Authors: Yoshihara Sachio 
Published: February 2020

The aim of this paper is to develop a, lightweight and forceful Magnetic abrasive particles (MAP). Magnetic field assisted finishing was performed to examine the fabricated MAPs. A new MAPs based on the nickel-cobalt diamond composite plated plastic ball have been prepared successfully. The finishing results for “Damascene” sample or “Copper Overhang Generated in the Direct Laser Via Process” have suggested the powerful ability of the new MAPs to the field of the fabrication of various electronic devices.

Magnetic abrasive particles (MAPs) are crucial to ensure finishing quality and accuracy in magnetic abrasive finishing (MAF) processing. Conventional MAPs consist of ferrous particles and abrasive, such as Al2O3, SiC, ZrO2, B4C as well as diamond, cubic boron nitride, MgO, CeO2 or fumed silica. The MAPs can be used as unbound, loosely bound or bound. One of them KMX 80 (trade name) are frequently used as commercial magnetic abrasives.　This abrasive particle consists of dispersed aluminum oxide grains in iron matrix particles with the average diameter of 80 micrometer.

Here, ferrous particles, which are mostly conventional used magnetic particle in MAF process, provide force of grinding via magnetic field. But due to the corrosion and softness of ferrous materials, the post-cleaning of the surface finished by the MAPs containing ferrous particles becomes the most time-consuming and critical procedure in some ultra-precision MAF processing, other magnetic particles should be urgent to be developed to replace the conventional ferrous particles.

In this paper a, lightweight and forceful MAP has been developed. And Magnetic field assisted finishing was performed to examine the fabricated MAPs.

A new bound MAP based on the electroless cobalt-nickel boron, 20 nm sized diamond composite plating to plastic balls was prepared. 10 mirometer sized Plastic ball was used as support here for MAPs growth due to its lightweight properties.

“Damascene” sample were supplied by Selete Co. Ltd. The original surface of the sample was covered with over-coated copper layer. Thus supplied sample was used as a workpiece.

The AFM images of the surface profiles was captured after finishing by KMX80 (3 mins) followed by the cobalt-nickel diamond composite plated plastic balls for 8 mins. The AFM images for the sample after MAF suggests that nano meter-sized surface smoothing could be attained. The best finishing conditions will be needed to be investigated in future.

Another approach of MAP to electronic devices has been tried for removal of copper overhang generated in the direct Laser via process by use of magnetic polishing method. In recent years, via holes has been used for the connection of external wiring and internal wiring of the multilayer substrate. When copper foil of wiring layer was processed by laser, melted copper was adhered, so projections called “overhang” are formed around the opening of via hole. Adhesiveness and flatness of plating will be decreased by the overhang, therefore removal process of them will be indispensable. Therefore magnetic polishing method has been tried as a novel removal technique in this study. In conclusion, the finishing results for “Overhang” sample have suggest the powerful ability of the new MAPs to the field of the fabrication of the FWB(Printed Wiring Board) devices.