How to Use Desiccants with Moisture Vapor Barrier Bags

3M-1-6KDES1200What is Desiccant?

Desiccant is a drying agent that is used to absorb moisture from the air inside moisture barrier bags. Desiccant absorbs moisture vapor (humidity) from the air left inside the barrier bag after it has been sealed. Any moisture that penetrates the bag will also be absorbed. Desiccant remains dry to the touch even when its fully saturated with moisture vapor.

How is Desiccant Purchased?

Desiccant is sold by the unit or fractional unit. One unit of desiccant will absorb a specific amount of moisture. A unit weights 28 grams, or 1 ounce. The pouches of desiccant are placed into metal pails to keep the desiccant dry during shipping and storage.

How is Desiccant Packaged?

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

Why are Electronics Moisture Sensitive?

Certain kinds of electronic devices called “Surface Mount Devices” or SMD’s are mounted on a circuit card by high temperature soldering. The body of the SMD is made from plastic that absorbs moisture from the air. When the case is heated during soldering, the moisture inside turns to steam and may break the device as the steam escapes. Keeping SMD’s dry before soldering means that the devices will not be damaged.

How Much Desiccant Do I Need?

Method 1 per MIL-P-116

  • Formula: Unit = 0.011 x bag area in square inches
  • Example: 10″ x 20″ barrier bag
  • Find Bag Area: 10″ x 20″ x 2″ sides: 400 Sq. In.
  • Apply Formula: Units = 0.011 x 400 Sq. In. = 4.4

Method 2 per EIA 583 (This formula allows you to tailor the desiccant to your specific needs)

What do you need to know?

  • Bag area
  • Bag MVTR
  • Months of storage
  • Maximum interior humidity (MIH)

Formula

  • Units = 0.231 x Bag Area x Bag MVTR x Months Divided by Moisture Capacity

Example

  • For a 10″ x 20″ bag with a 0.02 MVTR, a 12 month storage time and a MIH of 20%

Apply Formula Units

  • 0.231 x 400 Sq. In. x 0.02 MVTR x 12 Divided by 4.8g/unit – Units =4.6
  • Use 4.5 Units of Desiccant

Moisture Capacity

  • 10% MIH = 3.0 g/unit
  • 20% MIH = 4.8 g/unit
  • 30% MIH = 5.8 g/unit
  • 40% MIH = 6.2 g/unit

Where do I Purchase Desiccant?

You can find all of Production Automation’s Desiccant options online as well as Moisture Vapor Barrier Bags, and Humidity Indicator Cards.

PAC offers a full range of products to help you store or ship sensitive materials:

Visit PAC online at www.gotopac.com to view all of the products we offer, or contact us at 888.903.0333 or [email protected] for any questions you might have.

We also have a live chat feature on our website, so you can contact a sales rep at any time during your shopping experience. We want to help you get the right products at the right price!

 

© Desco Industries

 

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