Charactarization of Formaldehyde-Free Electro-Less Copper Plating for Semi-Additive Process

Abstract

Typically, industrial electroless copper plating solutions use formaldehyde as a reducing agent. However, since formaldehyde has a strong odor and is a carcinogenic substance, it has an adverse effect on the working environment and the human body. Therefore, an electro-less copper plating solution containing no formaldehyde is desired. We have researched and developed a formaldehyde-free electro-less copper plating solution and evaluated its properties for applications such as panel level package (PLP). Price is the main reason for selecting agents with reducing power to copper for use in the plating market. We promoted to develop the plating solution using sodium hypophosphite as a reducing agent, which is the next least expensive after formalin solution. The reducing agent used in this plating solution has low catalytic activity for copper. As a result, when the palladium catalyst on the resin is covered with copper plating, the plating deposition rate is reduced. In order to prevent the deposition reaction from stopping during plating, a metal salt with high catalytic activity for this reducing agent is plated. The method of adding to the liquid was carried out. As a result, the bath stability of the development bath is excellent because no Cannizzaro reaction or disproportionate reaction of the first copper ion occurs, unlike ordinary electroless copper plating solutions. This is a major advantage in terms of running costs and requirements for ancillary the plating equipment. When the characteristics of the plating film by development bath were examined, the internal stress was found to be as low as 150 MPa on the tensile side. The adhesion to the ABF resin was high, ranging from 500 to 700 gf/cm. Also it exhibits excellent plating deposition inside blind via hole (BVH) which is equivalent to that of general electro-less copper plating solution, it can be applied to semi-additive process package boards where electro-less copper plating film is etched.