Method of transporting and applying a surface treatment liquid using gas bubbles

摘要

A method is provided for dynamically transporting and applying a liquid to a surface, such as the bottom surface of a printed wiring assembly (PWA). The liquid may comprise an aqueous reducing agent solution for removing surface oxides prior to a soldering operation. The PWA is placed in proximity with the treatment solution held in a reservoir. Gas bubbles generated in the solution dynamically elevate and apply the solution to the bottom surface of the PWA. The bubbles may be formed by a non-oxidizing gas, such as nitrogen, introduced through a porous material. A flat surface of porous material produces a uniform bubble size that allows controlled and precise application of the solution. The porous material and the gas pressure may be varied to so that the bubbles elevate the solution to the desired level. The gas bubbles are short-lived (without surfactants) so that rapid transport, replenishment, and regeneration of the solution can be achieved. Moreover, nitrogen gas is injected at the PWA surface as the bubbles burst so that reaction of the solution or the PWA with oxygen is minimized. The gas bubble method also minimizes the pressure that forces treatment liquid through PWA through-holes to the top surface where it can be difficult to remove.