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One of the biggest risks to electronic components during packaging, storage, and transit is moisture (humidity). This is because moisture can greatly damage electronic components if not properly protected. Changing levels of moisture can lead to container damage and adverse effects like rust or deterioration of metal surfaces. It can also cause condensation on electronic components, increasing the risk of corrosion, short circuits, and other failures. In this guide, we will cover why dry packaging is needed, when dry packaging should be used, the items required to create a dry package such as a moisture barrier bag, and a step-by-step guide on how to create an effective dry package.
Before looking at how to dry package electronic components, it’s important to understand why moisture-sensitive devices require proper protection.
Dry packaging plays a crucial role in protecting SMDs for several reasons:
Example of a Plastic-Packaged Integrated Circuit:
Surface mount devices, or SMDs, are plastic-encased integrated circuits, commonly referred to as an IC, chip, or device. An example of this can be seen in the image below. An SMD consists of a circuit (or die) enclosed within a plastic body, with metallic leads that facilitate connection to a circuit board. The plastic body is susceptible to absorbing moisture from the surrounding air, which can impact the performance and reliability of the device.
SMDs are mounted to printed circuit boards (PCBs) through a process known as reflow soldering, which involves reheating the solder on the pads. This technique ensures that the circuit board, device leads, and device casing all reach the necessary temperature for secure and reliable bonding.
During the reflow soldering process, the device is positioned on a printed circuit board (PCB) and heated in an oven to melt the solder, forming connections between the leads and the board’s pads. However, moisture trapped inside the device casing expands at a faster rate than the casing itself, which can lead to rupture. If the casing breaks, it may result in damage such as delamination, “popcorning”, or even complete component failure.
It is important to keep surface mount devices dry or slowly baked under controlled conditions, ensuring moisture is removed on the device. Devices that are shipped without low-moisture packaging require baking to remove absorbed moisture. This process can take up to 24 hours, leading to production delays and additional costs for temperature and humidity control equipment.
Keeping surface mount devices dry between manufacture and the point of reflow soldering has led to the development of moisture barrier bags, otherwise known as vapour barrier bags.
Moisture barrier bags are not moisture vapour-proof and do not remove moisture. Over time, moisture vapour can gradually penetrate the bag, potentially affecting the contents.
To solve this problem, a desiccant should be inserted into the bag to reduce moisture (humidity). Desiccants are ideal for keeping enclosed items, like electronic components, computer chips, loaded and vacuum packed JEDEC trays, safe and protected from moisture damage.
Humidity indicator cards should also be placed inside the bag to show the relative humidity with moisture-sensitive spots which change colour.
As a final barrier against moisture, vacuum packing can be used to remove air that contains moisture before the bag is heat-sealed, further protecting the contents.
There are four key elements needed to create a reliable moisture-proof dry package:
1. Moisture Barrier Bags (MBBs)
Moisture barrier bags are specially designed to shield electronic components from moisture ingress and electrostatic discharge (ESD). Their multi-layered construction effectively prevents moisture vapour from getting inside the bag and provides ESD shielding to protect static sensitive electronic components from ESD damage.
Unlike a static shielding bag, moisture barrier bags are opaque, meaning you can’t see through them. Bags with a solid foil layer provide superior moisture protection, allowing less moisture to pass through by reducing vapour transmission. This is measured using the Moisture Vapour Transmission Rate (MVTR), which calculates the amount of moisture (in grams) passing through 100 square inches of MBB film. The lower the MVTR, the better the moisture resistance. According to JEDEC standards, the maximum allowed MVTR is </=0.02 grams. For comparison, a 3.5 mil metallised MBB has an MVTR of 0.02, while a 4.0 mil solid foil bag boasts an MVTR of 0.0003—making it approximately 100 times more moisture-resistant.
2. Desiccant Bag
Desiccants are moisture-absorbing agents enclosed in porous pouches, designed to absorb excess moisture from the air trapped inside a sealed barrier bag. Even when fully saturated, they stay dry, helping to maintain a consistently low internal humidity level. The amount of desiccant needed depends on the interior surface area of the bag being used. Using too little desiccant won’t provide enough moisture protection, while using too much can be wasteful. As a general guideline, one unit of desiccant is recommended for every 0.28 cubic foot of packaging space to effectively safeguard electronics from humidity. Learn more: Types and Uses of Desiccant
3. Humidity Indicator Card (HIC)
Humidity Indicator Cards are printed with moisture-sensitive spots that change colour depending on the relative humidity inside the package. For example, some HICs have a visible colour change from blue to pink or yellow to brown. The humidity inside the moisture barrier bags can be monitored by the HIC inside. This provides a quick and easy way to check moisture levels upon opening, helping to maintain the effectiveness of the moisture protection system. HICs can also help the user to determine if baking the component or device is needed.
4. Moisture Sensitivity Level Labels (MSL)
Moisture sensitivity level labels show how long an SMD can be exposed to ambient air before soldering. The label must be placed on the outside of the moisture barrier bag and clearly marked with the correct MSL level. If the level isn’t listed, check the barcode label for details.
Now that you’re familiar with the key components of a dry ESD package, follow these steps to create a secure, moisture-resistant package that keeps your SMDs safe from moisture and electrostatic discharge.
1. Prepare the tray stack – Place the desiccant and humidity indicator card on top of the tray stack. The trays carry the devices. Store desiccants in an airtight container when not in use to maintain their effectiveness.
2. Label the Moisture Barrier Bag – Attach the MSL label on the bag and mark the correct sensitivity level on the label.
3. Insert tray stack into the MBB – Place the tray stack (with the desiccant and HIC) into the moisture barrier bag.
4. Seal the bag – Use a vacuum sealer to remove excess air from the bag and then heat-seal the bag closed. Please note, it is not recommended to take all the air out of the bag. A slight evacuation ensures a secure fit for storage or transit.
5. Ready to use – Now your devices are safe from moisture and electrostatic discharge (ESD).
If moisture-sensitive devices (MSDs) are exposed to ambient air for too long, they must be baked before reflow soldering. Check the table below for industry-standard bake times and temperatures based on MSL levels.
Tip: Always keep sealed MBBs in a temperature-controlled, low-humidity environment to ensure maximum protection.
Moisture Barrier Bags, desiccants, and humidity indicator cards are crucial for safeguarding ESD-sensitive devices and PCBs from moisture damage. They should always be used together to ensure maximum protection. However, it is important to use all three tools correctly in order to be effective. Additionally, heat-sealing your Moisture Barrier Bag with a vacuum sealer is essential to remove moisture-laden air from the package, ensuring your electronic components are protected.
Prevent moisture and electrostatic discharge from compromising your electronic components! Using moisture barrier bags, desiccants, and humidity indicator cards ensures effective moisture control and reliable ESD protection for your surface mount devices.
Need further help on creating a dry packaging system? Contact our team on 01793 511000 or sales@bondline.co.uk where we’d be happy to help! You can also get in touch by filling in the form below.
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Bondline Electronics Ltd are a leading manufacturer and supplier of static control products within the ESD industry. Products such as Flexible and Rigid Packaging, Bench Matting, Wrist Straps, Heel Grounders and Shoes, ESD Protective Clothing and Gloves, Test and Measurement Equipment along with many storage and handling solutions.
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