The Gel Plating Process for selective gold metallization of electronic packages

Electroless plating processes are currently used to deposit metals such as copper, nickel, and gold on selective areas of an electronic package. Many contaminants are introduced into the plating solution during electroless plating because high volumes of substrates are passed through a single plating tank. Costly bath maintenance is required to prevent decomposition of these large plating baths. In addition, commercially used electroless gold plating baths have a pH around 14. This high pH, aqueous solution is not compatible with easily corroded materials found in electronic packages such as certain polymeric components, aluminum nitride substrates, and resist layers. Therefore, the Gel Plating Process has been developed as a commercially viable alternative to the current electroless gold plating process. The Gel Plating Process deposits gold only on desired features and eliminates contact between the corrosive medium and the surface of the package. A plating gel is formulated based on electroless gold plating bath chemistry and screen printed onto the areas of the substrate which require gold metallization. Under the proper plating conditions, gold metal deposits directly under the gel print. Currently, this process has been designed to deposit a one micron gold plate thickness from a 500 micron wet gel print. Advantages of the Gel Plating Process include: variation of gold thickness on the same substrate, reduction of substrate etching by minimizing the exposure of the substrate surface to the corrosive plating components, elimination of costly bath maintenance and contamination issues, and reduction of plating costs partially due to the lower volume of plating medium utilized.