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Atmospheric Fluxless Removal of Thin Metal Oxides from Substrates


A process for removal of thin layers of surface metal oxides from a component has been developed in which the use of a mixture of a reducing gas (typically 5% hydrogen in nitrogen) in an activated environment is required. The atmospheric condition activated environment requires some level of a conductive substrate along with a simple electrode assembly. Application of a pulsed direct current (DC) voltage across the electrodes in the presence of the substrate and the reducing gas mixture result in removal of surface oxides from metals. Other methods for removal of surface metal oxides include flux and fluxless methods. Traditionally, flux is a material is utilized in applications such as soldering to remove surface oxides; examples include ammonium chloride, hydrochloric acid, rosin and other compounds. Fluxes are typically a component of the soldering paste containing the metallic species used to form the ultimate solder joint. During the heating process, fluxes and fluxing by-products mostly evaporate, but can also cause detrimental effects on the resulting solder bond. Additionally, in many soldering applications, flux residues are not totally removed during the heating steps and some post-cleaning process must be used to remove these flux residues. To overcome these limitations, dry (fluxless) soldering has been studied for many years. One method is utilizing hydrogen-containing atmospheres to provide a possible reducing medium. Unfortunately, temperatures required for hydrogen alone to rapidly reduce oxides are much higher than normal soldering temperature range. Other processes for fluxless soldering include vacuum plasmas or remote chambers for activation of gas species in order to lower the temperature for such oxide removal. These processes all result in much higher capital costs for users.


  • No residue needs to be cleaned after the solder reflow
  • No labor required to clean furnace contaminants
  • No void formation inside reflowed solder
  • Non flammable hydrogen concentrations are used for the process
  • Atmospheric conditions are utilized in a potentially continuous process
  • Low temperature solder reflow
  • Low power DC requirement
  • Lower operation and capital costs
  • No remote chamber requirement, can be incorporated into a reflow furnace apparatus
  • Removal of oxides from both base metals and solder metals IP Table


Priority Patent Docket No.

Hydrogen Fluxless Soldering by Electron Attachment US 6,776,330
Hydrogen Fluxless Soldering by Electron Attachment US20050241671 A1
Apparatus and method for removal of surface oxides via fluxless technique involving electron attachment and remote ion generation US20040231597 A1
Electrode assembly for the removal of surface oxides by electron attachment US 7,563,380
Removal of surface oxides by electron attachment for wafer bumping applications US 7,387,738


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Fluxless Removal of Thin Metal Oxides from Substrates under Atmospheric Conditions
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