Moisture-Sensitive Components Need Sensible Handling

As moisture-sensitive components become more prevalent in the supply chain, low- and mid-volume manufacturers need to adjust their materials handling and manufacturing processes to prevent manufacturing defects and early-life failures.

With smaller package sizes becoming mainstream in all levels of product design, more mid-volume and low-volume manufacturers are encountering moisture-sensitive parts. We are seeing ICs, LEDs, and even connectors that require special handling.

Moisture absorbed from the air by a plastic IC package expands rapidly during solder reflow. Smaller, thinner packages with less space around the die are most prone to damage. Sometimes it is visible, such as when packages burst open (sometimes called the popcorn effect). Other times, internal damage such as delamination or cracking is invisible to inspection but can cause early-life product failure.

The JEDEC J-STD-020 standard defines moisture sensitivity levels (MSLs) and corresponding floor life, or how long a part with a given MSL can remain outside dry storage before reflow. Levels range from MSL 2 (a floor life of one year) to MSL 5A (a floor life of 24 hours). MSL 1 parts are not moisture-sensitive, and, in the extreme, MSL 6 parts must always be baked before use.

Parts that exceed their floor life must have the moisture baked out slowly before solder reflow. Default bake cycles range from 48 hours at 125°C to 79 days at 40°C, but they can be reduced depending on MSL and package thickness, according to J-STD-020.

The floor life limit adds complexity to manufacturing and component storage. Your contract manufacturer needs procedures to monitor cumulative floor time and environmental conditions, as well as equipment such as vacuum systems for resealing bags, dry-box storage areas, and bake ovens for parts and boards. At Z-AXIS, moisture-sensitive parts arrive sealed in moisture barrier bags with desiccant and a humidity indicator card. The MSL is printed on the bag label (see photo). We inspect the bags for tears and store them unopened until needed.

Upon opening the bag, we check the humidity indicator card to confirm the parts have not been exposed to moisture during storage. We then assemble and reflow the boards within the floor life window. If a second reflow is needed, it must be done within the floor life window, or the entire board must be baked between reflow operations.

Floor life is cumulative. Tracking cumulative floor life is easier in high-volume manufacturing, where entire reels of parts are used in a single run. But in high-mix manufacturing, we build products in many smaller runs over the course of a year or more. It is very common for us to return partially used reels to storage after each run. Partial reels are resealed in moisture barrier bags with a humidity indicator card and fresh desiccant. The bags are heat sealed with light air evacuation. Every time a bag is opened and resealed, we record the time and date and track cumulative exposure time.

MSL ratings are at ≤ 30°C and 60% relative humidity, so we have to derate the floor life if parts are exposed to higher levels. Conversely, lower factory temperature and humidity will extend floor life by an amount depending on package size and thickness, per the J-STD-033C standard. We could conceivably extend the floor life of MSL 2a parts from 28 days to indefinite by maintaining relative humidity of less than 30%, but this would conflict with the need to maintain relative humidity more than 30% for ESD protection.

By now, you might be wondering why we don't just bake moisture-sensitive parts before use. Unfortunately, this hurts solderability, material flow, and production time. It is better to store moisture-sensitive parts properly, keep careful records of cumulative floor time, and schedule production accordingly.

If you supply moisture-sensitive parts to your contract manufacturer, make sure that your own handling procedures are compliant, and that you provide accurate documentation to your partner. We have received moisture-sensitive parts in loose bags without desiccant, requiring us to bake before use. We have received partial reels of parts sealed in moisture-barrier bags with a vacuum high enough to crack the reel. Improper handling leads to production delays, higher costs (if your manufacturer passes them on to you), and potential product failures.

6 comments on “Moisture-Sensitive Components Need Sensible Handling

  1. t.alex
    November 25, 2013

    I am curious to hear more about the baking process. How is it done ? Will it degrade the component?

  2. Daniel
    November 26, 2013

    “As moisture-sensitive components become more prevalent in the supply chain, low- and mid-volume manufacturers need to adjust their materials handling and manufacturing processes to prevent manufacturing defects and early-life failures.”

    Michael, you are right about the moisture-sensitive components and the way it has to be handled. I know many cases that such components are coming either in a seal broken package (due to negligence in handling)or sharing the package with other similar sensitive components. I personally feels that experts has to handle such sensitive components, otherwise its life can be gone.

  3. SunitaT
    November 26, 2013

    Can bubble wrapping things, especially electrical goods, prevent them from being moistened? Most manufacturers wrap their electrical goods and try to save money at the same time. Most packaged goods only go through a radiation testing and air flow testing. However if the moisture is present in the electrical from beforehand (can happen during an assembly line rollout) then such pieces are generally discarded. 

  4. Michael Allen
    November 26, 2013

    For baking you use an oven which can maintain the required bake temperature at less than 5% relative humidity. The bake oven gently and slowly evaporates or “bakes off” any moisture inside the component without causing damage that the sudden high heat of solder reflow would. The duration and temperature of baking depend on the MSD rating, package type and thickness, and how long the part has exceeded its floor life. There is a detailed chart in the JDEC standard J-STD-033C. Baking does degrade the component, mainly by causing oxidation that can reduce its solderability.

  5. t.alex
    November 26, 2013

    No, i think bubble-wrap is mainly for transporting, not for storage.

  6. tnguyengp
    November 26, 2013

    Electro Static Discharge is an issue that is becoming increasingly more of a concern in the computer/electronics industry. Electronic components are composed of micro-miniature traces and structures of alternating layers that may be insulative, conductive or semi-conductive. Rapid electrostatic discharge (ESD) can cause damage to these underlying structures via the traces of the component.

    In general, if you are storing ESDS devices for prolonged periods of time (6 months or more) or if the devices are sensitive to corrosion, than you should package these materials in either an MVB (Moisture Vapor Barrier) bag with a desiccant pack to absorb any moisture that was sealed in static shielding bags with a desiccant pack. The difference between an MVB film and a metal-in film is about 1 magnitude in the moisture vapor transmission rate (grams of water/100 in2/24 hours @ 100 oF). Moisture sensitive ESDS devices should only be packaged in an MVB bag.

    Than Nguyen

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