How To Clean Indium Wire or Indium Foil？

Indium exhibits self-passivating properties. At typical room temperature, a thin oxide layer forms on the surface of indium Wire or Indium Foil, measuring between 80-100 Angstroms thick.Typically, this oxide layer is not substantial enough to impede the wetting of indium onto a substrate, particularly when flux is applied. However, even in the absence of flux, indium should still readily form joints or coat surfaces without difficulty.

Should the application require an oxide-free joint and flux cannot be utilized, the removal of the indium oxide can be achieved through the following steps:

Remove Surface Contaminants: Start by removing any visible contaminants from the surface of the indium wire or foil. You can use a soft brush or cloth to gently wipe away dust, dirt, or other debris.
Solvent Cleaning: Prepare a cleaning solution using a mild solvent that is compatible with indium. Isopropyl alcohol (IPA) is commonly used for this purpose. Dip a clean, lint-free cloth or swab into the solvent and gently wipe the surface of the indium wire or foil to remove any remaining contaminants. Ensure that the solvent evaporates completely before proceeding to the next step.
Acid Cleaning (if necessary): If the indium surface is heavily oxidized or contaminated, you may need to use an acid solution to clean it effectively. Dilute hydrochloric acid (HCl) or sulfuric acid (H2SO4) can be used for this purpose. However, exercise caution when working with acids, and always follow proper safety precautions. Etch the indium in 10% HCl for 1 minute to remove the surface oxides, then rinse thoroughly with distilled water to neutralize any remaining acid.
Rinse with Distilled Water: Rinse the indium in DI water to remove the acid and rinse the indium in isopropyl alcohol or acetone to remove the water. Ensure thorough rinsing to prevent any remaining cleaning agents from interfering with subsequent processes.
Drying: Once cleaned and rinsed, carefully pat the indium wire or foil dry with a clean, lint-free cloth or allow it blow dry with dry nitrogen or allow to air dry. Avoid using compressed air, as it may introduce contaminants or damage the indium surface.
If the etched indium won’t be used right away, it’s advisable to store it in a nitrogen dry box. Alternatively, you can submerge the etched indium in clean acetone to shield it from exposure to air.

Although the etching procedure effectively eliminates oxides, it also exposes a new surface on the Indium Foil or Indium Wire, which becomes susceptible to oxidation. Typically, oxidation initiates promptly upon exposure of freshly etched indium to air. Initially, the oxide layer measures around 30-40 Angstroms in thickness. Within 2-3 days of air exposure, the oxide layer reaches its passivating thickness of 80-100 Angstroms.

Indium Foil or Indium Wire possesses a remarkable characteristic of cold welding to itself once the oxides are eliminated. Throughout the etching process, it’s crucial to ensure that units of indium Foil remain separated to prevent them from sticking together. If they do become attached, separating them without distorting the indium can be exceedingly challenging.

It’s important to note that the specific cleaning method may vary depending on the level of contamination and the application requirements. Always refer to the manufacturer’s recommendations and safety guidelines when cleaning indium wire or foil.