Desiccant

Are your static and moisture sensitive components protected by your packaging? Learn how to minimize potential product failures by protecting your products from Electrostatic Discharge (ESD) and moisture during the manufacture, transportation, and storage process.

Why are Moisture Barrier Bags important?

Moisture Barrier Bags (MBB) shield ESD sensitive devices from 2 potential risks:

  1. The Faraday Cage created when using these bags protects contents from ESD Damage.
  2. Specialized layers of film controlling the Moisture Vapor Transfer Rate (MVTR) also protect contents from moisture.
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Moisture Barrier Bags – more information

“Desiccant” and “humidity indicator cards” must be used for proper moisture protection.

But what exactly are “desiccant” and “humidity indicator cards” and how are they used? These are the questions we will clarify in today’s blog post.

What is desiccant?

Desiccant is a drying agent that absorbs moisture from its surrounding area. Desiccant will stay dry to the touch even when it is fully saturated with moisture.

In a Moisture Barrier Bag it is used to ‘soak up’ moisture from the air inside the bag AFTER it has been sealed. Any moisture that gets through the bag from the outside will also be absorbed.

How is desiccant purchased?

Desiccant is available as a “unit” or fractional “unit”. A unit of desiccant absorbs a specific amount of moisture. One unit of desiccant weighs about 28g.

How is desiccant packaged?

Desiccant is packed in small sealed pouches made from a white plastic called “Tyvek” or brown “Kraft” paper. Tyvek pouches are very clean and Sulphur free. Kraft pouches are economical.

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A desiccant pouch – more information

Pouches of desiccant are placed into metal pails – this ensures the desiccant is kept dry during transport and storage.

How much desiccant do you need?

There are 2 different methods you can use:

  1. Method 1 per MIL-P-116
    Formula: Unit = 0.011 x bag area in square inches
    What you need: Bag area (2 times the surface area of your bag as there are 2 sides to a bag)
    Example: 10” x 20” MBB bag
    Apply formula: 0.011 x (10” x 20” x 2) = 4.4 rounded up to 4.5 units of desiccant
  2. Method 2 per EIA 583 (allows you to tailor desiccant to your specific needs)
    Formula: Unit = 0.231 x Bag Area x Bag MVTR x Months divided by Moisture Capacity
    What you need: Bag area, Bag MVTR, Months of Storage, Maximum Interior Humidity (MIH), Moisture capacity table below:
10% MIH 3.0 g/unit
20% MIH 4.8 g/unit
30% MIH 5.8 g/unit
40% MIH 6.2 g/unit

Example: 10” x 20” bag with a 0.02 MVTR, a 12 month storage time and a MIH of 20%
Apply formula: 0.231 x (10″ x 20″ x 2) x (0.02) x (12/4.8) = 4.62 rounded down to 4.5 units of desiccant

What is a humidity indicator card?

A humidity indicator card allows for quick visual inspection of the relative humidity levels within its surrounding area. They are printed with moisture sensitive spots which respond to various levels of humidity with a visible color change from blue to pink.

In a Moisture Barrier Bag they provide a low-cost method of verifying the effectiveness of the moisture barrier packaging. If you are using Moisture Barrier Bags, moisture will be an issue in your application so you’re obviously aiming for as little moisture as possible. However, if you happen to open your MBB and the humidity indicator card shows a relative humidity of 60%, you’ll know that the contents of your bag have been exposed to moisture and may not be safe for use anymore.

How are humidity indicator cards purchased?

Humidity indicator cards come in many shapes and forms. Some will show relative humidity from 10% – 60%; others from 5% to 15%. Depending on the sensitivity of your application to moisture, the correct type of card should be chosen.

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A humidity indicator card – more information

Bear in mind that not all humidity indicator cards are reversible. Some cards will measure the relative humidity only once and then halt at that reading. These types of humidity indicator cards are NOT re-usable. This is important to know so make sure you check before purchasing!

How are humidity indicator cards packaged?

Humidity indicator cards are sold in containers. It is recommended that cards are stored in their original un-opened canister in a dry, well ventilated room with a reasonably consistent temperature of 20°C. Humidity indicator cards should not be stored in ultraviolet sunlight, moisture or heat.

How many humidity indicator cards do you need?

One humidity indicator card per MBB is needed for proper verification of relative humidity.

Conclusion

Moisture Barrier Bags, desiccant and humidity indicator cards all play a very unique and important role when protecting ESD sensitive devices from moisture.

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Protect your static and moisture sensitive components with proper packaging

They should always be used together to ensure maximum protection. However, remember that all three tools need to be used correctly as otherwise all your efforts have been in vain. And don’t forget: your Moisture Barrier Bag must be heat sealed with a vacuum sealer to eliminate the amount of “moisture laden air” within the package.

Find the right protective packaging for your sensitive components! Check out the SCS Moisture Barrier Bag Selection Guide and Humidity Indicator Card and Desiccant Chart to find the right packaging products for your application.

If your company has an ESD Control Program per ANSI/ESD S20.20 in place, you need to define ESD protective packaging for ESD sensitive items (ESDs).
The Organization shall prepare an ESD Control Program Plan that addresses each of the requirements of the Program. Those requirements include:
– Training
– Product Qualification
– Compliance Verification
– Grounding / Equipotential Bonding Systems
– Personnel Grounding
– ESD Protected Area (EPA) Requirements
– Packaging Systems
– Marking” [ANSI/ESD S20.20 clause 7.1 ESD Control Program Plan]

But where do you start? Don’t panic – we’re here to help and we’ll be following the guidelines set-out in the ESD Standard.

Definition and Purpose of ESD Protective Packaging
ESD Protective Packaging covers any materials coming into direct contact with ESD sensitive devices during handling, shipping and storage. You don’t need to worry about secondary or exterior packaging unless it’s used for ESD protection purposes.
Packaging for ESD sensitive items is commonly derived by modifying existing packaging to prevent the packaging itself from causing static damage. The packaging generally retains physical and environmental protective qualities. ESD protective packaging has been modified further to prevent other sources of static electricity from damaging a packaged item.“ [ANSI/ESD S541 Foreword]

The fundamentals of ESD control include grounding all conductors in the EPA. ESD packaging will have special material composition to lower the resistance so that when grounded, electrostatic charges will be removed to ground thus protecting your ESD sensitive devices inside.
Transportation of electrostatic sensitive devices requires packaging that provides protection from electrostatic hazards in the transportation or storage system. In the case of an EPA designed with continuous grounding of all conductors and dissipative items (including personnel), packaging may not be necessary.” [ANSI/ESD S541 clause 6. Packaging Application Requirements]

Example of ESD Packaging

Packaging is to be determined for all material movements inside and outside of the ESD Protected Area (EPA). Best practice is to define the required packaging or material handling item on the product’s bill of materials. Remember: the ESD packaging is just as important as a component part.

Customer contract packaging can take precedence, but otherwise “the organization shall define ESD protective packaging requirements, both inside and outside the EPA per ANSI/ESD S541 or in accordance with the contract, purchase order, drawing or other documentation necessary to meet customer requirements.” [ANSI/ESD S20.20 clause 8.4 Packaging]

Choosing your ESD Protective Packaging
Numerous factors need to be taken into consideration when choosing your ESD protective packaging including the “environment and device sensitivity.” [ANSI/ESD S541 Annex A.1 Environment and Device Sensitivity]
It is best recommended to follow these 6 steps:

    1. Understand the product sensitivity
      You can gather information about the ESD sensitivity of an item by either measuring it in-house, contacting the manufacturer of the product or by analyzing published ESD sensitivity data.
    2. Determine the distribution environment for the packaged product
      Knowing the environment in which the product is shipped and how it will be handled is extremely important. Humidity and temperature are the main factors to consider when it comes to choosing the right type of packaging for your ESD sensitive items. If items are susceptible to moisture, a barrier material should be chosen to prevent excessive humidity exposure. On the other hand, condensation may occur inside the packaging if temperatures vary around the dew point of the established interior conditions. In those instances, desiccant should be put inside of the package or the air should be removed from the package before shipment.

A Moisture Barrier Bag – click here for more information

  1. Determine the type of packaging system that is best suited for the intended application
    The first step is to choose low charging or static dissipative materials when in contact with ESD sensitive devices. Many companies also require the packaging to protect the contents from a direct discharge or exposure to electric fields. In addition to these requirements, there are further questions that need to be asked:

    • Returnable or reusable packaging?
    • Disposable or one-time only packaging?
    • Aesthetic requirements for packaging?
  2. Select and test packaging materials
    Test methods are explained in ANSI/ESD S541 and will classify packaging materials as conductive, static dissipative or insulative.
  3. Design a packaging systemOnce the ESD sensitivity and distribution environment have been evaluated and available materials have been selected, the design of the packaging system can begin. Per the ANSI/ESD S541, the following general rules apply:
    • Inside an EPA:
      Packaging used within an EPA (that satisfies the minimum requirements of ANSI/ESD S20.20) shall be:

      • Low charge generation.
      • Dissipative or conductive materials for intimate contact.Items sensitive to < 100 volts human body model may need additional protection depending on application and program  plan requirements.”
        [ANSI/ESD S541 clause 6.1 Inside an EPA]
    • Outside an EPA:
      Transportation of sensitive products outside of an EPA shall require packaging that provides:

      • Low charge generation.
      • Dissipative or conductive materials for intimate contact.
      • A structure that provides electrostatic discharge shielding.
        [ANSI/ESD S541 clause 6.2 Outside an EPA]

    Example of ESD Packaging

    In addition to these guidelines, there may be additional factors that should be considered, e.g.:

    • Cost/value relationship: The cost of the packaging compared to the total value of the contents is important. Some companies choose less expensive packaging for less valuable parts.
    • Handling: If rigorous handling is expected, cushioned packaging may need to be considered.
  4. Test the final packaging design for effectiveness
    It is highly recommended to subject packages to the type of hazards that can be expected during shipments. These tests can, for example, involve the following:

    • High voltage discharges to the exterior of the packaging
    • Simulated over the road vibration
    • Drop tests
    • Environmental exposure

Final thoughts on ESD Protective Packaging
Now that you have an understanding of the factors to consider when choosing your ESD Protective Packaging, you’re ready to implement the above guidelines. ESD packaging comes in all sorts of shapes and forms so bear in mind to not just look at bags when deciding what type of packaging to choose.
Also, remember that ESD packaging should be marked. We’ll cover the specifics in a later post.