Study Of Electroless Metallic Plating On The Non-active Substrates Induced By Surface Defects

The non active substrates possess excellent properties of metal and non-metal materials after surface metallization which are widely used in material, machine, electronics and other industries. While it can’t be synthesized through a simple physical disposition resulted from the lack of surface activity of substrates and the difference of the properties between metals and nonmetals. Nowadays, several surface metallization process containing vacuum coating, spray coating, electroless plating and electroplating etc. are discussed. With the advantage of simple equipment, low cost and good quality of plating, the electroless plating is a promising process. And the successful electroless plating focus on the pretreatment process. Traditional pretreatments were mainly involved in activation and sensitization or one-step activation; high technology assisting noble metal activation process including microwave radiation, UV treatment; non noble metal activation process containing grafting organic interlayer, laser irradiation, plasma assisted activation process. All pretreatment methods talked above are complicated with high cost and high requirements of equipment and operation staffs. In this paper, a new simplified pretreatment method for non active substrate （plastic, Al2O3, SiC powders） is proposed which produced a lot of surface defects to obtain a certain activity. After direct electroless plating, dense, uniform metallic plating was prepared. This pretreatment can greatly reduce the cost and simplify the metallization process that is of great practical significance to the practical production. The main results of this paper are as follows:1) For plastics, folds and uneven steps as nucleation center on PC engineering plastic surface were obtained during the pretreatment and after copper electroless plating, the pretreated plastic surface obtained smooth, dense and uniformly distributed Cu coatings. The growth mechanism of the copper plating layer is mainly characterized below:the reactants are dispersed and adsorbed onto surface defects with catalytic activity; the Cu particles settle after reduction; and the Cu particle growth process involves the repeated gathering of nano-level Cu grains to form physically agglomerated Cu granules.2) For the Al₂O₃ ceramics, ultrasonic and pretreatment solution assisted electroless plating are also utilized. After electroless copper plating, layer on the alumina surface is successfully prepared. But due to the limitation of the pretreatment liquid itself and the stability of the substrate, the electroless plating is still flawed. Afterwords, the follow-up treatment are in progress, one is second electroless plating process which increased the use of bath stabilizers and effectively improve the performance of coating leading to the formation of uniform and dense copper coating on the surface of alumina. Another subsequent process is including different heat treatment process at different temperature. The heat treatment process of 800℃ can effectively improve the coating performance, while with high thermal stress, which is prone to peeling off, and is not conducive to the combination of coating and substrate. Therefore, the most appropriate heat treatment process is at 500℃.3) In order to complete the system of non active substrate, powders （SiC powder） as a finally non active substrate is investigated. After activation pretreatment, the surface of SiC powders occurred lots of defects which lead to a successful electroless nickel plating with ultrasonic at room temperature.