Why is MSL (Moisture Sensitivity Level) set?

When reviewing semiconductor specifications and datasheets, you may find the MSL (Moisture Sensitivity Level) listed. Furthermore, some products are shipped in vacuum packaging, with specific handling conditions after opening. This level of control is necessary because of the relationship between semiconductor packaging and moisture.

Currently, many semiconductor products use packages made of molded resin. While these packages offer high reliability as electronic components, they can absorb small amounts of moisture depending on the storage environment. Therefore, semiconductor manufacturers evaluate the characteristics of each product and specify appropriate handling conditions.

So why is moisture absorption a problem?

MSL is particularly closely related to reflow soldering, which is performed during the assembly process. In the reflow process, components are exposed to a high-temperature environment for a short period of time. At this time, moisture absorbed inside the package can rapidly expand, potentially generating stress inside the package. Considering these effects, semiconductor manufacturers and industry associations evaluate packages that have absorbed moisture.

On the other hand, electronic devices after assembly are also exposed to the surrounding environment on a daily basis. However, after assembly, semiconductors are soldered to a substrate and used as a product in the state envisioned during the design phase. MSL primarily targets the period from when semiconductors are stored and opened before assembly until they undergo the reflow process. In other words, the problem is not moisture absorption itself, but rather "going through the high-temperature reflow process while hydrated."

Against this backdrop, JEDEC defines MSL as a rating indicating susceptibility to damage during reflow soldering. MSL does not indicate the "quality of the component," but rather serves as a guideline for handling conditions according to the package characteristics. For example, even products from the same manufacturer may have different MSLs if the package structure and size differ. Also, even devices with similar functions may have different storage conditions and handling conditions after opening depending on the package used. In other words, MSL is not merely a management number. It is set as an indicator that connects the characteristics of semiconductor packages with the mounting process, and understanding its background makes it easier to understand why each manufacturer sets storage, opening, and mounting conditions.

What is the purpose of storage, opening, and implementation conditions?

When handling semiconductor products, they are often delivered in moisture-proof packaging, and may include desiccants or humidity indicator cards. Furthermore, some products may have specified storage periods after opening and mounting conditions. These conditions might make you wonder, "Why are they managed in such detail?" The reason semiconductors have storage and post-opening usage conditions isn't simply to complicate management. It's deeply related to the characteristics of the semiconductor package and the mounting process.

Many semiconductor packages can absorb small amounts of moisture depending on the storage environment. On the other hand, they are exposed to high temperatures during the reflow soldering process. Therefore, semiconductor manufacturers define storage conditions and handling conditions after opening based on evaluation results for each product. For example, vacuum packaging and desiccants are used at the time of delivery as mechanisms to minimize environmental impact during transportation and storage. Humidity indicator cards are also used as a guide to check the condition inside the packaging. All of these are efforts that take into account the moisture absorption characteristics of the product. MSL is used to organize these handling conditions. Multiple levels of MSL are defined, and the handling conditions for storage, opening, and assembly differ for each level.

*Please refer to the JEDEC standards and each manufacturer's documentation for detailed conditions.

It's important to understand that the MSL value doesn't represent the superiority or inferiority of a product's performance or quality. MSL is merely an indicator of the package's moisture absorption characteristics, and different values are set for each product. Even products from the same manufacturer may have different MSL values depending on the package structure and size, and even devices with similar functions may have different handling conditions depending on the package used.

Rules such as vacuum packaging, desiccants, and usage conditions after opening may seem like individual regulations at first glance. However, they all share the common principle of "handling the package while considering its moisture absorption characteristics." MSL (Material Safety Law) can be considered one indicator for understanding this principle.

Quality Management from an MSL Perspective

When people think of quality control, they often picture inspection processes and defect analysis. However, looking at it through the lens of MSL (Material Safety Law), it becomes clear that quality control encompasses a wide range of activities, from component storage to assembly, not just the verification work after the product is completed. For example, semiconductor manufacturers set MSLs for each product and define storage, unpacking, and assembly conditions accordingly. This demonstrates that quality control extends not only to the product itself, but also to the environment in which the product is stored and the conditions under which it is assembled.

Furthermore, as evidenced by the differing handling conditions depending on the MSL, understanding not only the device's functions and performance but also its package characteristics is crucial for properly handling semiconductor products. Considering this, quality control is not solely the responsibility of the quality department. It involves multiple processes, including design, procurement, inventory management, production technology, and assembly. The MSL can be considered one indicator that links package characteristics with handling conditions within this context.

The goal isn't simply to memorize the MSL (Material Storage Limit) values. Rather, the important thing is to understand the background behind why manufacturers specify storage, unpacking, and mounting conditions. Knowing the MSL metric makes the connection between semiconductor package characteristics and quality control clearer, which can deepen your understanding of the product.

Summary

MSL (Moisture Sensitivity Level) is an index set according to the moisture absorption characteristics of semiconductor packages. Semiconductor manufacturers define storage, opening, and mounting conditions based on the relationship between package characteristics and the mounting process. Furthermore, the MSL level does not indicate the superiority or inferiority of product performance or quality, but rather is used as a guideline for determining appropriate handling conditions for each product. Therefore, rules such as vacuum packaging, desiccants, and usage conditions after opening are not individual regulations, but rather based on common principles that take package characteristics into consideration.

Understanding MSLs reveals not only the meaning of storage, opening, and mounting conditions, but also that quality control encompasses not only the inspection process but also the handling of components. When handling semiconductors, why not pay attention not only to the device's function and performance, but also to the package characteristics, including the MSL?

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