My sample has Tin electroplated on Copper. I want to selectively etch the Tin.
Dear Tanmay Konnur Please do recommend my answer if helpful.
Selective etching to remove tin while retaining copper can be achieved through the use of specific etchants. One commonly used etchant for this purpose is a solution of ferric chloride (FeCl₃). Ferric chloride is known for its selectivity in etching tin without significantly attacking copper. Here's a general guideline for using ferric chloride as an etchant:
### Ferric Chloride Etching Procedure:
1. **Prepare the Etchant Solution:**
- Dissolve ferric chloride powder in water to create a solution. The concentration of the solution can vary, but a common starting point is around 40-50% concentration. You can adjust the concentration based on the specific requirements of your etching process.
2. **Preparation of the Copper-Tin Sample:**
- Ensure that your copper-tin sample is properly cleaned and free of contaminants. Mask or protect the copper areas that you want to retain using an appropriate masking material, such as resist or tape.
3. **Etching Process:**
- Immerse the sample in the ferric chloride solution. Monitor the etching process carefully to control the time and ensure selective removal of tin. Agitate the solution if necessary to enhance etching uniformity.
4. **Rinse and Neutralize:**
- After the desired etching is achieved, remove the sample from the ferric chloride solution and rinse it thoroughly with water to stop the etching process. Neutralize any remaining ferric chloride on the sample using an appropriate neutralizing agent.
5. **Cleaning and Inspection:**
- Clean the sample to remove any residues and inspect the etched areas to confirm the selective removal of tin while preserving the copper regions.
### Important Notes:
- **Safety Precautions:**
- Ferric chloride is corrosive and can stain. Follow proper safety precautions, including wearing protective clothing, gloves, and safety glasses. Work in a well-ventilated area or under a fume hood.
- **Temperature Control:**
- The etching rate can be influenced by temperature. Controlling the temperature of the ferric chloride solution can help achieve more precise etching control.
- **Masking:**
- Properly mask the copper areas using a suitable material to ensure they are protected from the etchant.
- **Experimentation:**
- Conduct small-scale experiments to optimize the etching conditions for your specific copper-tin sample.
Please note that the effectiveness of the etching process may depend on the specific composition and structure of your copper-tin sample. Always test the etching process on a small, representative sample before applying it to your final sample.
Tin dissolves in hydrochloric acid as well as in NaOH. Copper does not react with these two reagents.
Hi Tobias Makuochukwu Onyia
Some readers will probably find your outline of ferric chloride solutions preparation and use quite useful. Unfortunately, this is NOT the right reagent for protecting copper. In fact, solutions of ferric chloride are known to etch copper, and are specifically used - and sold - for this purpose. See for example
https://media.jacksonsart.com/pdf/Etching_COPPER_with_ferric_chloride.pdf
If you think about it, this is no surprise. Looking up the potentials of relevant half-reactions (from Lange's Handbook but surely the Handbook of Chemistry and Physics has similar numbers),
Fe(3+) + e(-) = Fe(2+), E(0) = +0.771 V
Cu(2+) + 2e(-) = Cu(0), E(0) = +0.334 V
The stronger oxidant (Fe(3+) oxidizes the stronger reductant (Cu(0)). All is well with the world.
Ah, but what about the chloride ions, you may say? Actually they don't matter much in this case because the complexes of both Fe(3+) and Cu(2+) with chloride are quite weak, so the equilibrium position is not affected.