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:

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

*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.

*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:

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
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.

*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.

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.

In our last post, we talked about the ESD protective packaging requirements for ESD sensitive items and provided you with 6 steps to choose the correct type of packaging. We thought today we could go in a little bit more detail and introduce you to some types of packaging and how to use them. If you read our recent post on Tips to Fight ESD, you will remember how important it is to protect your ESD sensitive items when leaving an EPA. Yet, too often we see customers who have the perfect EPA, but when it comes to transporting and storing their precious components, it’s all falling apart.

Packaging required for transporting and storing ESD sensitive items
During storage and transportation outside of an EPA, it is recommended that ESD sensitive components and assemblies are enclosed in packaging that possesses the ESD control property of shielding. See our last post for more details.

Remember:

In ‘shielding’ we utilize the fact that electrostatic charges and discharges take the path of least resistance.
The charge will be either positive or negative; otherwise the charge will balance out and there will be no charge.
Charges repel so electrostatic charges will reside on the outer surface.

The Faraday Cage effect
A Faraday Cage effect can protect ESD sensitive items in a shielding bag or other container with a shielding layer. To complete the enclosure, make sure to place lids on boxes or containers and close shielding bags.

*Cover must be in place to create Faraday Cage and shield contents.*

Types of shielding packaging
The below list gives a few examples of what types of shielding packaging is available on the market. This list is by no means complete; there are many different options out there – just make sure the specifications state “shielding” properties.

Metal-In Shielding Bags
ESD bags which protect ESD sensitive items. The ESD shielding limits energy penetration from electrostatic charges and discharge. They offer good see-through clarity. Available with and without zipper.

Example of a Metal-In Shielding Bag – Click here for more information
Metal-Out Shielding Bags
Integral antistatic and low tribocharging bags which will not electrostatically charge contents during movement. Bags have an aluminium metal outer layer of laminated film. Available with and without zipper.

Example of a Metal-Out Shielding Bag – Click here for more information
Moisture Barrier Bags
Offer ESD and moisture protection and can be used to pack SMD reels or trays.

Example of a Moisture Barrier Bag – Click here for more information
Cushioned Shielding Bags
These bags combine the “Faraday Cage” and mechanical protection. They shield about twice as well as normal shielding bags of equivalent size.

Example of a Cushioned Shielding Bag – Click here for more information

Additional options for storing ESD sensitive items
Do you have the following in place?

ESD flooring
Grounded personnel (using foot grounders)
Grounded racking

IF (and this is a BIG IF) the above requirements are fulfilled, you can use conductive bags or containers to store your ESD sensitive items. Conductive materials have a low electrical resistance so electrons flow easily across the surface. Charges will go to ground if bags or containers are handled by a grounded operator or are stored on a grounded surface.

Conductive materials come in many different shapes and forms:

Conductive Black Bags
Tough and puncture resistant bags which are made of linear polyethylene with carbon added. The bags are heat sealable.

*Example of a Conductive Black Film – Click here for more information*

Rigid Conductive Boxes
Provide good ESD and mechanical protection. Boxes are supplied with or without high density foam for insertion of component leads or low density foam which acts as a cushioning material.
PCB Containers
Are flat based and can be stacked. They are made of injection moulded conductive polypropylene.

Again, there are many more options available on the market so make sure you do your research.

Note: we do not recommend using conductive packaging to transport ESD sensitive devices. Also, pink antistatic and pink antistatic bubble bags are not suited for storing or transporting ESD sensitive components.

Final thoughts
Packaging with holes, tears or gaps should not be used as the contents may be able to extend outside the enclosure and lose their shielding as well as mechanical protection.

Also, do not staple ESD bags shut. The metal staple provides a conductive path from the outside of the ESD bag to the inside. The use of a metal staple would undermine the effectiveness of the ESD bag making a conductive path for charges outside the bag to charge or discharge to ESD sensitive components inside the bag. To close an ESD bag, it is recommended to heat seal or use ESD tape or labels after the opening of the bag has been folded over. Alternatively, you can use ESD bags with a zipper.

Packaging

Moisture Barrier Bags, Desiccant and Humidity Indicator Cards