Study on the Effect of Forced Convection on Pd Ion Adsorption and Cu Electroless Deposition

Abstract

Copper electroless deposition for the formation of electrically conductive seed layers is important in the manufacturing process of printed circuit boards. As the size of electrical devices decreases, the seed layer also needs to be thinner and its uniformity is highly stressed. In this study, Pd ion adsorption and Cu electroless deposition, which are the most crucial steps in seed layer deposition, were controlled through forced convection. Without forced convection, the seed layers at the top and bottom sides of the microvia are of different thicknesses, which can cause defects. The application of forced convection in Pd ion adsorption uniformly deposited the seed layer by suppressing the adsorption of Pd ions on the top side of the microvia. Furthermore, forced convection on copper electroless deposition enhanced overall mass transfer of reactants such as cupric ions and formaldehyde, and accompanying the deposition rate on the top and bottom sides, which balanced the thickness of the seed layer on the top and bottom sides. Thus, forced convection in Pd ion adsorption and Cu electroless deposition compensated for the suppression of the Pd ion adsorption and improved the uniformity of seed layers on the microvia substrates.