Patent ID: 7387738

Claim:
A method of removing metal oxides from the surface of a substrate comprising a plurality of solder bumps, the method comprising: providing the substrate which is connected to a first electrode within a heating chamber; providing a second electrode that is proximal to the first electrode and the substrate wherein the second electrode has a negative bias in electric potential relative to the first electrode and wherein at least a portion of the surface comprising the plurality of solder bumps is exposed to the second electrode; passing a gas mixture comprising from 0.1% to 4% by volume hydrogen and from 1% to 99.9% by volume nitrogen between the first and the second electrodes wherein the pressure of the gas mixture ranges from 10 to 20 psia; supplying voltage between the first and the second electrodes to generate electrons from the second electrode wherein at least a portion of the electrons attach to the hydrogen to form negatively charged hydrogen ions; contacting the substrate with the negatively charged hydrogen ions to reduce the metal oxides on the surface of the substrate; and changing polarity of the second electrode to a positive bias in electric potential to remove at least a portion of the electrons from the surface of the substrate and return the electrons to the second electrode.