What is Moisture Sensitivity Level? How MSL Chart Defined

In PCB assembly, certain surface mount devices can be sensitive to moisture, and I was surprised that they can be damaged if exposed to moisture in humid environments when subjected to reflow soldering.

Moisture sensitivity level (MSL) is a rating established by JEDEC for electronic components that indicates the floor life of the component and provides the maximum allowable exposure for electronic components in humid environments. I’ve considered all 8 MSL classifications and explained them in detail in this article.

What are The Moisture Sensitivity Levels?

The Moisture Sensitivity Levels (MSL) is a standardized classification system used in the electronics industry to determine the sensitivity of electronic components to prevent moisture-related issues.

The MSL categorizes electronic components into different levels based on their sensitivity to moisture exposure. It is a standardized classification system introduced by the Joint Electron Device Engineering Council (JEDEC). The MSL classification helps to understand the handling electronics industry professionals regarding handling and storage guidelines for various components such as QFP, BGA, TSSOP, SOP, etc.

MSL 1Components in this category are considered to be the least sensitive to moisture.
MSL 2Components with MSL 2 classification have a low sensitivity to moisture.
MSL 3Components in MSL 3 are moderately sensitive to moisture
MSL 4Components with MSL 4 classification are more sensitive to moisture.
MSL 5MSL 5 components are highly sensitive to moisture.
MSL 6Components classified as MSL 6 are extremely sensitive to moisture.

Moisture Sensitivity Levels are denoted by a numeric value, typically ranging from MSL 1 to MSL 6. In the next section of this article, we will discuss various moisture sensitivity levels and their classifications in detail. We also explore the MSL level chart and MSL baking requirements specifications.

MSL Level Descriptions

Below is an explanation of the standard moisture sensitivity level (MSL) used by IPC/JEDEC. Expect Moisture Sensitivity Level chart 6 – Mandatory to Bake before use.

MSL LevelMSL RatingDescription
MSL 1Unlimited shelf lifeComponents can be stored indefinitely
MSL 2aFloor life ≤ 4 weeksComponents must be mounted within 4 weeks
MSL 2Floor life ≤ 1 yearComponents must be mounted within 1 year
MSL 2bFloor life ≤ 2 yearsComponents must be mounted within 2 years
MSL 3Floor life ≤ 1 weekComponents must be mounted within 1 week
MSL 4Floor life ≤ 72 hoursComponents must be mounted within 72 hours
MSL 5aFloor life ≤ 48 hoursComponents must be mounted within 48 hours
MSL 5Floor life ≤ 24 hoursComponents must be mounted within 24 hours

Presently, there are seven categories of msl levels for electronic components. Unsurprisingly, devices with low floor levels tend to last longer on floors. Every package manufacturer wants to achieve level 1, which means their package has an unlimited floor life.

As the industry standard for moisture sensitivity definitions, JEDEC defines a classification of moisture sensitivity. By setting a fixed reflow temperature, such as in the following Table, this standard will identify the moisture sensitivity level, allowing the user to properly store and handle the devices and prevent damage from subsequent thermal/mechanical activities such as attachment reflow and repairs.

MSL Level Chart

The Moisture Sensitivity Level (MSL) chart or table is used in the electronics industry to categorize and identify the moisture sensitivity of different surface mount devices (SMDs). These levels are critical for the proper handling, storage, and baking of SMDs to prevent damage during solder reflow processes. Here’s a basic MSL chart/table:

When the moisture sensitivity level bake time is exposed to production ambient conditions of 60% relative humidity for a sufficient time, it can be dried by high- or low-temperature baking, as shown in the MSL level table in the next slide re-baking before reflow.

Here’s a table outlining the MSL levels and their respective floor life and baking conditions:

MSL LevelFloor Life (hrs)Baking Conditions (°C)Maximum Time Limit (°C)
MSL 1UnlimitedNot ApplicableNot Applicable
MSL 2a4125°C for 24 hours30°C
MSL 2b12125°C for 24 hours30°C
MSL 2Not EstablishedNot EstablishedNot Established
MSL 3168125°C for 24 hours30°C
MSL 472125°C for 24 hours30°C
MSL 5a48125°C for 24 hours30°C
MSL 5b24125°C for 24 hours30°C
MSL 5Not EstablishedNot EstablishedNot Established

Plastic packages can be detached from semiconductor chips or lead frames by this internal vapor pressure, causing cracks internally or externally and damaging thin films and wire bonds. When faced with a moist integrated circuit package, soldering may cause it to bulge or even explode in severe cases.

Moisture can enter semiconductor devices encapsulated in plastic when improperly stored, handled, or packaged. A package that is enclosed in plastic can become damaged when moisture inside vaporizes during soldering.

The floor lifetime begins when the Moisture Barrier Bag is opened. The following table will be used for baking if an MBB is opened and its components will not be used within the specified floor life.

MSL Baking Table and Consideration

Here are some essential considerations for the proper handling of components to mitigate moisture sensitivity:

Understanding MSL Ratings: Electronic components are classified into diverse MSL levels, typically ranging from MSL 1 (indicating the highest sensitivity) to MSL 6 (indicating the least sensitivity). Understanding the MSL level of your components is crucial.

Storage Conditions: Components should be stored in a dry environment with meticulously controlled humidity levels. They should be placed in hermetically sealed moisture-barrier bags, accompanied by desiccant packs to preclude moisture infiltration.

Pre-Baking: In cases where components have been exposed to moisture or have exceeded their floor life (which is the maximum permissible duration for components to be exposed to ambient conditions), they may necessitate pre-baking before the soldering process. It is imperative to adhere to the recommendations provided in the component datasheet or the manufacturer’s guidelines regarding the required pre-bake conditions.

Baking Temperature and Time: Components should be subjected to the appropriate temperature and duration for baking. Typically, components are baked at temperatures ranging from 100°C to 125°C for durations ranging from 4 to 24 hours. The specific conditions are contingent upon the component’s MSL rating and moisture content.

Handling and Contamination Control: When handling components, it is vital to employ procedures that are compliant with Electrostatic Discharge (ESD) safety standards to avert ESD-induced damage. Minimizing contact with component surfaces is essential to curtail contamination.

The pre-baking and post-baking steps in MSD component baking can be classified into two types. Components prepared for dry packing are pre-baked, while those that have passed their shelf life are post-baked.

The temperature and baking time must be carefully calculated, as improper baking can cause lead oxidation, leading to poor solderability. It’s really important to understand how to bake at the right temperature. I have included a J-STD-33 chart below, detailing ideal baking conditions. 

What You Must Know About Moisture Sensitive Devices (MSDs)

As you know the temperatures involved in SMT reflow soldering are from 210°C to 270°C. Moisture inside a plastic package turns to steam and expands rapidly in reflow soldering. The High temperatures can cause trapped moisture to rapidly expand, thereby physically damaging the component.

Under certain conditions, the force from this expanding moisture can cause internal mechanical damage and device failure. In the most severe cases, the stress can result in external package cracks. This is commonly referred to as the “popcorn phenomenon” because the internal stress causes the package to bulge and crack with an audible “pop”.

How to avoid thermal damage in the SMT process?

Preventing thermal damage during the Surface Mount Technology (SMT) process is essential to maintain the reliability and functionality of electronic components. Here are key strategies to avoid thermal damage during SMT assembly:

Profile Optimization: Develop and refine solder reflow profiles carefully. Control temperature ramp-up, soaking, and cooling rates to prevent extreme thermal stresses on components. Always adhere to the recommended reflow profile provided by the component manufacturer.

Component Placement: Ensure precise component placement on the PCB. Proper orientation, alignment, and spacing following assembly guidelines are crucial to prevent heat concentration in specific areas.

Stencil Design: Carefully design the stencil to ensure consistent solder paste deposition. Use correct aperture sizes and patterns to avoid excess solder paste, which can lead to bridging and thermal issues.

Reflow Oven Calibration: Regularly calibrate and maintain the reflow oven to ensure it operates within specified temperature tolerances. This prevents temperature inconsistencies and overheating.

SMT component failures currently experienced by system manufacturers can be eliminated through the rigorous prevention of moisture absorption. By using moisture control procedures for handling dry-packed SMT magnetic components, can achieve significantly higher yields, reduce costly rework, and provide improved quality levels.

Important Definitions

Floor Live:- The allowable period after removal from a moisture barrier bag, dry storage, or dry bake and before the solder reflow process.

Humidity Indicator Card (HIC):- A card on which a moisture-sensitive chemical is applied such that it will make a significant, perceptible change in color (hue), typically from blue (dry) to pink (wet) when the indicated relative Humidity is exceeded.

A desiccant absorbent material is used to maintain a low relative humidity (less than 10% at 25°C) in moisture barrier bags for dry-packing moisture-sensitive devices. Desiccant may be a silica gel or other absorbent material packed in dustless pouches.

Moisture Barrier Bag (MBB): This bag limits water vapor transmission when packaging moisture-sensitive devices. The moisture barrier bag (dry pack bag) must be handled carefully so the plastic packages do not absorb moisture. Microsemi devices will remain safe as a result.

Shelf Life: A dry-packed moisture-sensitive device can only be stored in an unopened Moisture barrier bag (MBB) for a certain amount of time. The specified interior bag humidity does not exceed the recommended amount.

The shelf life for dry-packed moisture sensitivity level (MSL) SMD packages shall be a minimum of 12 months from the bag packed date when stored in a noncondensing atmospheric environment of <40°C/90% RH.

The Dry Pack consists of desiccant material and a humidity indicator card (HIC) sealed with the components inside a moisture barrier bag (MBB).

FAQ

Q. #1) How to determine moisture sensitivity level?

Ans. The moisture sensitivity level can be determined by the datasheet of the Package Qualification Summary Report. Based on that moisture sensitive devices can be exposed to ambient room conditions.

Q. #2) What is the moisture sensitivity level rating?

Ans. The Moisture Sensitivity Level (MSL) rating, Indicates the sensitivity of electronic components to moisture during the solder reflow process. It typically ranges from MSL 1 to MSL 6 and is specified by the component manufacturer in the datasheet.

Q. #3) What is moisture sensitivity level 1?

Ans: The moisture sensitivity level 1 guideline to avoid damage from moisture absorption is that you can store Unlimited (30℃ less than 85%RH) on the shop floor.

Q. #4) Why is the MSL level important?

The importance of MSL (Moisture Sensitivity Level) lies in its ability to signal the sensitivity of electronic components to moisture. Understanding the MSL level is critical because it helps prevent potential damage during the soldering process.

When components encounter moisture levels exceeding their MSL rating, it can result in defects such as “popcorning” or other forms of damage. This can compromise the reliability and functionality of electronic devices.

Conclusion – Wrapping it up

As a result, efficient moisture sensitivity level (MSL) control has become essential for EMS companies, particularly for high-reliability products.

As a result of moisture trapped inside the plastic packages, when they are soldered, they can be damaged. The moisture sensitivity of Microsemi’s plastic-packaged FPGAs is tested according to JEDEC procedures. The moisture Sensitivity Level (MSL) ranges from 3 to 4.

Suppose a user plans to store any device beyond the recommended floor life at a temperature or relative Humidity above their recommendation. In that case, Microsemi recommends the user perform a bake-out before reflow soldering.

Furthermore, medical, automotive, aerospace and defense markets require high mix/low volume assembly lines. In such environments, the total exposure time of MSDs increases significantly due to the cumulative effect of multiple machine feeder setups and product changeover.


Sources

  • JEDEC (Joint Electron Device Engineering Council): Website: JEDEC
  • Electronic Components Industry Association (ECIA): Website: ECIA
  • Electronic Device Failure Analysis Society (EDFAS): Website: EDFAS
  • IEEE (Institute of Electrical and Electronics Engineers): Website: IEEE
  • SEMIA (Surface Mount Equipment Manufacturers Association): Website: SEMIA

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  • Manoj Kumar Raghav

    Hello, this is Manoj, A Soldering and DIY Tool expert. Writing is one of my hobbies. With more than 20 years of broad experience. I love researching, discovering, and sharing new products with others, I hope you’ll enjoy the greatest featured products to make life easier, more fun, and more productive.

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2 thoughts on “What is Moisture Sensitivity Level? How MSL Chart Defined”

  1. The Understanding MSL Ratings paragraph contradicts the information at the beginning of the article. It says that MSL 1 is most sensitive and 6 is least sensitive, but the beginning of the article says opposite.

    Reply

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