Introduction

Moisture-sensitive devices (MSDs) are electronic components that are susceptible to damage from exposure to moisture. These devices are commonly used in a wide range of industries, including consumer electronics, automotive, aerospace, and medical devices. Moisture can cause a variety of issues, including delamination, popcorning, and corrosion, which can lead to device failure. Therefore, proper storage and handling of moisture-sensitive devices are critical to ensuring their reliability and performance.

This article will explore the various methods and best practices for the effective storage and handling of moisture-sensitive devices. We will discuss the importance of moisture sensitivity levels (MSLs), the use of dry storage cabinets, desiccants, and humidity indicator cards, as well as the role of proper packaging and handling procedures. Additionally, we will cover the importance of training and documentation in maintaining the integrity of moisture-sensitive devices.

Understanding Moisture Sensitivity Levels (MSLs)

Moisture sensitivity levels (MSLs) are a classification system used to indicate the susceptibility of electronic components to moisture-induced damage. The MSL rating is determined by the Joint Electron Device Engineering Council (JEDEC) and is based on the amount of time a device can be exposed to ambient conditions before it requires baking to remove moisture.

The MSL rating ranges from MSL 1 (least sensitive) to MSL 6 (most sensitive). Devices with higher MSL ratings require more stringent handling and storage conditions to prevent moisture absorption. Understanding the MSL rating of a device is crucial for determining the appropriate storage and handling procedures.

MSL Ratings and Floor Life

• MSL 1: Unlimited floor life at ≤30°C/85% RH. No special handling required.
• MSL 2: 1 year floor life at ≤30°C/60% RH.
• MSL 2a: 4 weeks floor life at ≤30°C/60% RH.
• MSL 3: 168 hours (1 week) floor life at ≤30°C/60% RH.
• MSL 4: 72 hours floor life at ≤30°C/60% RH.
• MSL 5: 48 hours floor life at ≤30°C/60% RH.
• MSL 5a: 24 hours floor life at ≤30°C/60% RH.
• MSL 6: 12 hours floor life at ≤30°C/60% RH. Must be baked before use if exposed beyond the floor life.

Dry Storage Cabinets

Dry storage cabinets are essential for maintaining the integrity of moisture-sensitive devices. These cabinets are designed to control humidity levels and prevent moisture absorption by the devices. Dry storage cabinets typically use desiccants or nitrogen purging to maintain low humidity levels.

Types of Dry Storage Cabinets

1. Desiccant-Based Cabinets: These cabinets use desiccants, such as silica gel, to absorb moisture from the air. The desiccant is periodically regenerated by heating to remove the absorbed moisture. Desiccant-based cabinets are cost-effective and suitable for storing devices with moderate MSL ratings.
2. Nitrogen-Purged Cabinets: These cabinets use nitrogen gas to displace moisture-laden air, creating a dry environment. Nitrogen-purged cabinets are more effective at maintaining extremely low humidity levels and are suitable for storing highly moisture-sensitive devices (MSL 5 and above).
3. Combination Cabinets: Some cabinets combine desiccant and nitrogen purging to provide an extra layer of protection against moisture. These cabinets are ideal for environments where humidity levels can fluctuate significantly.

Best Practices for Using Dry Storage Cabinets

• Regular Monitoring: Use humidity indicator cards or electronic sensors to monitor the humidity levels inside the cabinet. Ensure that the humidity remains within the recommended range for the MSL rating of the stored devices.
• Proper Sealing: Ensure that the cabinet doors are properly sealed to prevent moisture ingress. Regularly inspect the seals for wear and tear and replace them as needed.
• Device Organization: Organize devices within the cabinet based on their MSL ratings. Place the most sensitive devices in the most controlled areas of the cabinet.
• Baking: If devices have exceeded their floor life, they should be baked according to the manufacturer’s recommendations before being placed back into the dry storage cabinet.

Desiccants and Humidity Indicator Cards

Desiccants and humidity indicator cards are essential tools for managing moisture levels in the storage and handling of moisture-sensitive devices.

Desiccants

Desiccants are materials that absorb moisture from the air, helping to maintain a dry environment. Common desiccants include silica gel, molecular sieves, and clay. Desiccants are often used in dry storage cabinets, moisture barrier bags, and other packaging solutions.

Types of Desiccants

1. Silica Gel: Silica gel is the most commonly used desiccant. It is highly effective at absorbing moisture and can be regenerated by heating. Silica gel is available in various forms, including beads, packets, and canisters.
2. Molecular Sieves: Molecular sieves are synthetic zeolites with a uniform pore size that allows them to selectively absorb moisture. They are more effective than silica gel at low humidity levels and are often used in nitrogen-purged cabinets.
3. Clay Desiccants: Clay desiccants are made from naturally occurring minerals and are less expensive than silica gel and molecular sieves. However, they are less effective at low humidity levels and are typically used in less demanding applications.

Humidity Indicator Cards

Humidity indicator cards (HICs) are used to monitor the relative humidity (RH) inside storage containers and packaging. HICs contain moisture-sensitive chemicals that change color based on the humidity level. The color change provides a visual indication of whether the humidity is within the acceptable range.

Best Practices for Using Humidity Indicator Cards

• Placement: Place HICs in visible locations within storage containers and packaging to allow for easy monitoring.
• Calibration: Ensure that HICs are calibrated and provide accurate readings. Replace HICs that have been exposed to high humidity levels or have expired.
• Documentation: Record the humidity levels indicated by HICs as part of your quality control and documentation processes.

Proper Packaging for Moisture-Sensitive Devices

Proper packaging is critical for protecting moisture-sensitive devices during storage and transportation. The packaging must provide a moisture barrier and maintain a dry environment until the devices are ready for use.

Moisture Barrier Bags

Moisture barrier bags (MBBs) are specially designed bags that provide a high level of protection against moisture ingress. MBBs are made from multi-layered materials, including aluminum foil, polyethylene, and nylon, which create a barrier against moisture and oxygen.

Features of Moisture Barrier Bags

• Low Moisture Vapor Transmission Rate (MVTR): MBBs have a low MVTR, which means they allow very little moisture to pass through.
• Sealing: MBBs are typically sealed using heat sealing or zip-lock mechanisms to ensure an airtight closure.
• Desiccant Packs: MBBs often include desiccant packs to absorb any residual moisture inside the bag.
• Humidity Indicator Cards: MBBs may also include humidity indicator cards to monitor the humidity level inside the bag.

Vacuum Sealing

Vacuum sealing is another effective method for protecting moisture-sensitive devices. Vacuum sealing removes air from the packaging, creating a vacuum that prevents moisture from entering. Vacuum-sealed packages are often used in conjunction with moisture barrier bags for added protection.

Anti-Static Packaging

In addition to moisture protection, it is important to consider electrostatic discharge (ESD) protection when packaging moisture-sensitive devices. Anti-static packaging materials, such as conductive foam, anti-static bags, and ESD-safe trays, should be used to prevent ESD damage during handling and transportation.

Handling Procedures for Moisture-Sensitive Devices

Proper handling procedures are essential for preventing moisture absorption and damage to moisture-sensitive devices. The following best practices should be followed when handling MSDs:

1. Minimize Exposure to Ambient Conditions

• Time Management: Limit the amount of time that devices are exposed to ambient conditions. Devices should be stored in dry storage cabinets or moisture barrier bags when not in use.
• Controlled Environments: Handle devices in controlled environments with low humidity levels, such as cleanrooms or ESD-safe workstations.

2. Use ESD-Safe Handling Equipment

• ESD-Safe Tools: Use ESD-safe tools, such as tweezers, vacuum pick-up pens, and gloves, when handling moisture-sensitive devices.
• Grounding: Ensure that all handling equipment and personnel are properly grounded to prevent electrostatic discharge.

3. Follow Manufacturer Guidelines

• Baking: If devices have exceeded their floor life, follow the manufacturer’s guidelines for baking to remove moisture. Baking typically involves heating the devices at a specific temperature for a set period of time.
• Rehydration: Some devices may require rehydration after baking to restore their moisture content to the appropriate level. Follow the manufacturer’s recommendations for rehydration.

4. Training and Documentation

• Employee Training: Ensure that all personnel involved in the handling and storage of moisture-sensitive devices are properly trained. Training should cover MSL ratings, handling procedures, and the use of dry storage cabinets and packaging materials.
• Documentation: Maintain detailed records of the storage and handling of moisture-sensitive devices, including humidity levels, baking schedules, and any incidents of moisture exposure. Documentation is essential for quality control and traceability.

Conclusion

The effective storage and handling of moisture-sensitive devices are critical to ensuring their reliability and performance. By understanding moisture sensitivity levels, using dry storage cabinets, desiccants, and humidity indicator cards, and following proper packaging and handling procedures, manufacturers can prevent moisture-induced damage and extend the lifespan of their electronic components.

Additionally, training and documentation play a vital role in maintaining the integrity of moisture-sensitive devices. By implementing these best practices, manufacturers can minimize the risk of device failure, reduce costs associated with rework and scrap, and ensure the delivery of high-quality products to their customers.

In conclusion, the proper storage and handling of moisture-sensitive devices require a combination of the right equipment, materials, and procedures. By adhering to these guidelines, manufacturers can protect their investments and maintain the quality and reliability of their electronic components in even the most challenging environments.