In the field of electronic manufacturing, the MSL (Moisture Sensitivity Level) is a crucial parameter, directly related to the reliability of electronic components during the SMT reflow soldering process. The EMC team from Shanghai Leiditech Electronic often receives inquiries from customers about MSL. Today, we will systematically break down the reliability indicator for electronic components.

MSL stands for Moisture Sensitivity Level, which is a level standard formulated by JEDEC, which is used to characterize the sensitivity of electronic components to a humid environment and prevent the "popcorn" effect caused by the vaporization and expansion of internal moisture during reflow soldering. As a leading enterprise deeply engaged in semiconductor components for 16 years, Shanghai Leiditech Electronic is well aware of the crucial significance of correctly understanding and applying the MSL in ensuring product quality and enhancing production efficiency.

1、Classification of MSL Standards

According to the JEDEC J-STD-020D standard, MSL is divided into 8 levels, and the moisture-proof requirements for components of different levels vary significantly:

Leiditech EMC team reminds that the higher the MSL number, the higher the component's sensitivity to moisture and the shorter the time it is allowed to be exposed to the open environment. The classification of MSL is mainly based on the moisture absorption and heat resistance of the packaging materials. The higher the grade, the more easily the packaging materials absorb moisture and the more likely to be failure at high temperatures.

2、The influence of moisture on electronic components and the "popcorn" effect

The influence of moisture on electronic components is mainly reflected in two aspects: physical damage and chemical corrosion.

Regarding to the physical damage, when humidity-sensitive components are exposed to a humid environment, moisture can seep into the interior of the package. At the high temperature of 230-260℃ during SMT reflow soldering, moisture rapidly vaporizes and expands, triggering the "popcorn" effect, which leads to delamination of the package, damage to gold wire solder joints, microcracks in the chip, and the component might expand and bursting in severe cases. Shanghai Leiditech Electronic found in actual tests that the lead-free soldering process is much more sensitive to moisture due to its much higher temperature than the traditional lead-containing process. This is also the reason why the MSL grade is becoming increasingly important in the lead-free era.

Regarding to the chemical corrosion, ions such as potassium, sodium and chlorine in moisture can cause electrochemical corrosion. The formation of hydrated oxides weakens the adhesion between the packaging resin and the metal, which leads to the penetration of moisture and significantly reducing the reliability of components.

3、Testing methods and verification procedures for MSL

Component manufacturers are required to verify the MSL in accordance with the standard process. Shanghai Leiditech Electronic follows this specification to ensure product quality:

• Initial examination: Use a scanning acoustic microscope (SAT) to inspect the components and confirm that there are no defects or layering in the packaging.

• Baking dehydration: Bake for 1-2 hours within an environment of 125℃±5℃ and the humidity is <5% RH to remove internal moisture.

• Moisture absorption treatment: The baked components were exposed to 30℃/60%RH for 192 hours to simulate the moisture absorption of the components in the workshop environment.

• Reflow soldering simulation: Three standard peak temperature 260℃ reflow soldering tests were conducted on the moisture-absorbed components to simulate the heating conditions of the components during production, maintenance and re-production processes.

• Final examination: Use SAT and X-RAY to check the integrity of the package structure and conduct electrical function tests. If a component passes three reflow soldering tests without any layering or functional failure, its MSL is determined. If the component shows package cracking, the layering area exceeds 5% of the total package area, or the key electrical parameters exceed the allowable range, the MSL needs to be reduced and retested.

4、Suggestions for moisture-proof treatment of components of different MSL

Based on the practical experience of Shanghai Leiditech Electronic, the Leiditech EMC team provides moisture-proof solutions for components of various levels:

MSL 1 components: These components have the strongest resistance to moisture and can be stored indefinitely in an environment of ≤30°C/85% RH. It is recommended to use aluminum packaging and store them sealed together with coil desiccants to extend the lifespan of the components. ESD/TVS diodes, due to specific model and packaging differences, commonly have humidity sensitivity grades such as MSL1 and MSL3.

Msl2/2a components: Under an environment of ≤30°C/60% RH, MSL2 grade components can be stored for one year, and MSL2a grade components can be stored for four weeks. After opening, the workshop environment humidity must be strictly controlled to ≤60% RH and the temperature to ≤30°C, and the opening time must be recorded. If the storage time after opening exceeds the specified period, it is recommended to bake at 125℃/5%RH for 12 to 48 hours.

MSL3-5a components: Components with high humidity sensitivity levels require special attention to moisture-proofing

• Baking parameters: For components packaged in Trays, the baking temperature is typically 125℃±5℃, and the time is related to the thickness of the components (for example, 1.2mm thick components of MSL3 grade need to be baked for 9 hours). For components in Reel packaging, as they cannot come into direct contact with heat sources, the baking temperature is usually 40℃, the humidity is ≤5%RH, and the baking lasts for 9 days.

• Workshop life management: After opening, the exposure time must be strictly recorded, and welding must be completed within the workshop life. Components that have exceeded the lifespan of the workshop must be re-baked, and the time after baking can be recalculated.

• Moisture-proof packaging: Use the "Protection three-piece set" - moisture-proof bag (MBB), desiccant (silica gel/molecular sieve), and humidity indicator card (HIC) for sealed storage. When the 10%RH indicator point on the humidity indicator card changes color, it indicates that the component may have been damp and needs to be re-baked.

• Storage environment: Unopened components should be stored in an environment with a temperature of 25°C±5°C and a humidity that’s less than 40% RH.

MSL6 grade components: Extremely sensitive to moisture, with a workshop lifespan of only 12 hours. Before use, they need to be baked at 125℃/5%RH for more than 24 hours. After opening, they should be soldered immediately.

The MSL is a key reliability indicator in electronic manufacturing, especially after the miniaturization of components and the popularization of lead-free processes.

Leiditech EMC team suggests: Establish a component MSL database, recording the level, opening time and validity period. Control the workshop temperature and humidity at 25°C±5°C and <40% RH. Develop baking and storage solutions based on MSL and package types; High-grade components are given priority for production to avoid long-term exposure. Train employees regularly to enhance their application capabilities at the MSL. Managing the MSL components scientifically could reduce welding defects caused by moisture and enhance product reliability.