Wafer Storge Conditions

We have talked a lot about the long-term semiconductor storage that Force offers alongside its solutions to part obsolescence. But were you aware that the conditions of storing assembled semiconductors vary when compared to silicon wafer storage?

Storing semiconductor wafers just like storing assembled semiconductor devices requires carefully controlled conditions to maintain their quality and ensure optimal performance in future applications. Here are the best conditions for storing semiconductor wafers alongside how it varies from assembled semiconductor storage.

Relevant specifications: JEP160A & IEC TR 62258-3:2010

1. Temperature:

Room Temperature: Wafers like assembled components need to be stored at a stable room temperature, ideally between 17°C and 28°C. Care must be taken to avoid exposure to extreme temperatures.

Avoid Temperature Fluctuations: Maintain a consistent temperature to prevent thermal stress and potential damage to the wafers.

2. Humidity:

Low Humidity: Relative humidity should be kept low, ideally between 7% and 30%. High humidity can lead to oxidation and corrosion of the wafer surfaces. It is interesting and important to note that whilst assembled moisture sensitive semiconductors benefit from being held at a relative humidity of less than 5%, wafers should not be held at too low of a relative humidity as it can increase the risk of a pyroelectric effect which is the temporary accumulation of static electricity due to humidity changes and temperature shifts.

Avoid Condensation: Ensure that the environment does not allow condensation to form, as this can cause significant damage.

3. Clean Environment:

Cleanroom Standards: Store wafers in a cleanroom environment, adhering to at least ISO Class 5 (Class 100) cleanroom standards.

Particulate Control: Minimise the presence of particles, dust, and other contaminants that can adhere to or damage the wafer surfaces. Whilst FOD (Foreign objects) and particles are a concern for assembled components they are of particular concern for bare wafers and can disrupt both bond wire and die attach adhesion during assembly.

4. Packaging:

Proper Containers: Use specialised wafer carriers or containers designed for wafer storage. These should be made of materials that do not outgas or introduce contaminants. Whilst this is a concern for assembled packages as well and they should be stored in appropriate reels, tubes or trays wafers are far more fragile and sensitive to material contamination.

Anti-static Measures: Ensure the packaging materials have anti-static properties to prevent electrostatic discharge (ESD) damage.

5. Atmosphere:

Inert Atmosphere: For long-term storage, an inert atmosphere such as nitrogen should be used to reduce the risk of oxidation and contamination. Wafers should be stored in 99% pure nitrogen as per IEC TR 62258-3:2010 guidelines.

Sealed Containers: Store wafers in sealed containers to protect them from environmental contaminants and fluctuations in humidity and temperature.

6. Handling:

Minimise Handling: Handle wafers as little as possible to avoid introducing contaminants or causing physical damage. Wafers require a far higher degree of handling regulation due to their fragile nature and strict over assembled components.

Proper Tools: Use appropriate tools and follow standard procedures for handling to avoid scratches, cracks, and other physical damages.

7. Regular Monitoring:

Environmental Monitoring: Regularly monitor the storage conditions to ensure that temperature, humidity, and cleanliness levels are within the desired ranges.

Inspection: Periodically inspect the wafers and their storage conditions to detect any potential issues early.

By adhering to these guidelines, the quality and integrity of semiconductor wafers can be preserved, ensuring they remain suitable for future use in manufacturing processes. If you would like to know more about our long-term storage offerings, please drop us a line at [email protected].