Highly thermally conductive aluminum nitride ceramics were metalized by an electroless plated Ni-P film for the purpose of utilizing them in practical electronic circuit substrates. Aluminum nitride substrates were effectively etched by NaOH solution, and the adhesion strength between AIN and the Ni-P film was found to increase with an increase in surface roughness. At Ra value greater than 0.63 μm, adhesion strength increased to 2.0 kg mm-2, and a maximum of 3.0 kg mm-2 was obtained at Ra = 1.24 μm. The NaOH-etched AIN substrates, however, had a higher adhesion strength than substrates of abraded AIN or abraded Al2O3 with the same roughness. SEM observation showed that the surface of AIN substrate was selectively etched in the regions between adjoining large particles, and that Ni-P projections became effective interlocking points. It was therefore concluded that substrates of new aluminum nitride of high thermal conductivity are capable of being effectively metalized by electroless plating method, and that the main factor contributing to film adhesion strength is interlocking surface structures that are formed through selective etching by NaOH.
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