Chemical Etching Properties of Highly Thermal Conductive AIN Ceramics for Electroless Ni-P Metallization

The adhesion strength between AIN ceramics and electroless plated Ni-P film was investigated from the viewpoint of the chemical etching behavior. It was confirmed that chemical etching proceeds in two stages. The first etching stage is the selective dissolution of the Ca atoms, which are added as a sintering aid. Since the Ca atoms are mainly concentrated at the three grain junctions of triple points, the selective etching preferably proceeds along the triple points of the AIN grains. In this initial etching stage, the adhesion strength of the Ni-P plated film increases with an increase in the amount of the dissolved substrate. The deposition of electroless Ni-P plating at the triple points makes effective anchors of metal film against the substrate. At the second etching stage, the AIN grains also begin to be etched, and thus, the spaces between the grains are widened. In this etching stage, the adhesion strength gradually decreases with an increase in the dissolved amount of the AIN substrate. In conclusion, it is very important to consider the etching morphology and mechanism, including the process of substrate formation (i.e., sintering aid in the substrate) in order to get a higher adhesion strength for the electroless plating metallization.