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Are your static and moisture sensitive electronic devices protected by your packaging? Electrostatic Discharge (ESD) is a common threat in environments where electronics are manufactured and assembled. Electronic components such as printed circuit boards and semi-conductors are highly susceptible to ESD. If these sensitive components come into contact with a static charge then damage to the component is likely to follow. While the majority of people may know about ESD and the importance of protecting electronics from it, there is also another risk which many people do forget: moisture. In this article, we are going to address the problem with moisture, the risks it can have, and the types of ESD packaging (specifically Moisture Barrier Bags) that you can use to protect your electronics from moisture.
Moisture can be problematic in many industries; particularly where electronic devices are being manufactured or assembled. In environments where the humidity is above 50%, electronic devices are at risk to moisture damage. Surface Mount Devices (SMDs) are a typical example of electrical components that are prone to moisture damage. If not properly controlled, moisture can become trapped inside of Surface Mount Devices. During reflow soldering operations, the rapid increase in temperature can cause the trapped moisture inside of the Surface Mount Devices to expand and the delaminating of internal package interfaces. This can result in immediate product failure of the device. Often at times, it may cause damage to the device that only becomes apparent after the device is in use. In this instance, the product failure would be at the manufacturer’s expense.
It is important for Surface Mount Devices to be kept dry between the time of manufacture and the point of reflow soldering to dispel of any accumulated moisture. This is the key reason for the development of moisture barrier bags.
Moisture Barrier Bags, also known as a ‘dry package’, are used to help protect electronic products such as Surface Mount Devices (SMD’s) from moisture and electrostatic damage during storage, shipping, and manufacture. To use a Moisture Barrier Bag, an electronic device is simply placed inside the bag and enclosed with a metal or plastic shield that keeps the moisture vapour from entering inside the bag. The main objective of the bag is to protect the contents from accumulating moisture with a specialised layer of aluminium film which controls the Moisture Vapour Transmission Rate (MVTR). Additionally, the bag’s static dissipative layers shield (‘Faraday Cage’) the electronic products from electrostatic discharge.
As stated in the name, Moisture Barrier Bags are typically supplied in a bag form. Although, they can also be purchased in ESD film rolls. These can be customised to meet various requirements including bespoke sizes, printing, and thicknesses. Most Moisture Barrier Bags are opaque and light-tight to ensure the contents inside the bag cannot be seen from the outside, providing a layer of operational security. Their flexible structure allows for the Moisture Barrier Bag to be vacuum-sealed, moulding easily into the shape of the product. For packages that are shipped by sea, Moisture Barrier Bags are a good packing solution. This is because they can protect the moisture sensitive items from the humid sea environment, ensuring that items arrive just as they left.
Similar to the Moisture Barrier Bag is its cost-effective alternative Metallised Barrier Bags. While these work in the same way, they tend to have a lower Moisture Vapour Transmission Rate (MVTR).
The ESD Handbook ESD TR20.20 mentions the importance of moisture barrier bags in section 5.4.3.2.2 Temperature: “While only specialized materials and structures can control the interior temperature of a package, it is important to take possible temperature exposure into account when shipping electronic parts. It is particularly important to consider what happens to the interior of a package if the environment has high humidity. If the temperature varies across the dew point of the established interior environment of the package, condensation may occur. The interior of a package should either contain desiccant or the air should be evacuated from the package during the sealing process. The package itself should have a low WVTR.”
Here is an example of a Moisture Barrier Bag (left) and a Metallised Barrier Bag (right).
Industries such as electronics manufacturing and biomedical, as well as military and pharmaceutical, all require moisture barrier packaging. In-process components, medicinal goods, and various other products that are susceptible to moisture or oxidation are examples of products that will benefit greatly with the use of Moisture Barrier Bags.
Below are several types of applications and industries where Moisture Barrier Bags are typically used.
Moisture can be effectively controlled with a dry package. A dry package typically consists of three elements:
1) Moisture Barrier Bag
2) Desiccant Bag
3) Humidity Indicator Card
Ideally, all three components should be used together for maximum protection.
A desiccant bag is a drying agent which is used to attract moisture from the atmosphere. They are routinely added to packaging, such as Moisture Barrier Bags, to prevent the goods in transit or storage from being damaged by humidity or moisture.
As the desiccant attracts and absorbs moisture, it has a drying or dehumidifying effect. When this happens, moisture in the surrounding air is removed, which prevents it from damaging other objects in proximity.
The main purpose of a Humidity Indicator Card is to determine when products have been exposed to moisture and humidity above recommended storage levels. The cards indicate the relative humidity levels with moisture-sensitive spots – that are printed onto the card – which change colour from blue to pink. These cards are typically placed inside of Moisture Barrier Bags to monitor the humidity levels. When the bag is opened, the card can be examined for proper dryness inside the bag. This indicates whether the barrier bag and the desiccant have functioned correctly.
To ensure the protection of the product, a Moisture Barrier Bag is often vacuum-sealed to remove any air-containing moisture before the bag is then heat-sealed. While sealed, the bag will contain the product along with the desiccant bag and humidity indicator card.
When choosing a moisture barrier bag, there are several factors you need to consider to ensure the integrity of the protection. The three main factors you need to look for are the Moisture Vapour Transmission Rate (MVTR), the puncture resistance and the structure of the bag. This can be found in the product’s specifications.
This is the rate that water vapour passes through a specific area of barrier material. As Moisture Vapour Transmission Rate is reduced, dry storage time is increased and desiccant loading is reduced.
The lower the MVTR, the more effective the bag is at preventing water vapour from being transmitted. It is the metallised barrier bags that have the lowest MVTR, and that meet IPC/JEDECJ-STD-033 requirements.
MVTR is measured in grams of water vapour, per 100 square inches of barrier, per 24 hours (g/100in2/24hrs).
Puncture resistance, or otherwise known as puncture strength, is a test that determines the maximum pressure the bag film can withstand before puncturing. MIL-B-81705 requires a minimum of 10-lb resistance. In FTMS 101 MTH 2065, a specimen of bag material is placed in a flat cage with a hole through the centre. A 5-in. long rod with a 1/8-in. radius is pushed through the bag material. An electronic load cell measures the force (in pounds) required to puncture the material.
Moisture Barrier Bags can vary in their structure and material composition. Generally, there are three types of structures: Nylon/Foil/Poly, Tyvek™/Foil/Poly, and Aluminised Polyester/Poly.
Moisture Barrier Bags
Our moisture barrier bags have a three-layer construction, consisting of a static dissipative polyester surface, aluminium shield centre, and a static dissipative polyethylene bottom.
Metallised Barrier Bags
Our metallised barrier bags, on the other hand, have a four-layer construction, consisting of a static dissipative coating, a static dissipative polyester and aluminium shield centre, and a static dissipative propropylene bottom.
There are many benefits to using a Moisture Barrier Bag. Listed below are several benefits of our Moisture Barrier Bags.
As well as moisture barrier bags, there are a vast range of other types of ESD packaging for electrostatic control; the most common being static shielding bags, pink anti-static bags and ESD tape.
Each type of ESD packaging has their own purposes and applications. You can find more information on www.bondline.co.uk.
Now that we have covered the basics of moisture barrier bags, it is important to learn about the other types of ESD packaging. This can be achieved by taking an ESD training course with Bondline.
Bondline’s ESD training course will provide you will all the knowledge you need on ESD packaging as well as cover various ESD topics, offer demonstrations and a Q & A session. This can be tailored to your exact requirements.
If you’d like to get in touch with us about our ESD training course, please contact a member of our team on +44 (0)1793 511000, sales@bondline.co.uk or fill in the form below.
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