What Is Moisture Sensitivity Level, How Is MSL Level Defined

What is Moisture Sensitivity Level? MSL is an electronic standard that indicates when moisture-sensitive devices can be exposed to ambient room moisture. MSL is relevant to J-STD-020 packaging and handling precautions.

These are small semiconductor devices, such as QFP, BGA, TSSOP, SOP, etc. It is encapsulated with plastic compounds & other organic materials, which absorb moisture from atmospheric Humidity.

SMT components, the entire assembly is placed into reflow ovens. The temperature is raised close to the solder’s melting (210° to 250°C) point and then spiked up to liquefy the solder and create the connections between SMT component leads and the PCB.

In the entire PCB reflow soldering process, absorbed moisture is quickly turned into superheated steam, causing dramatic cracking or damage to the package. Most of this damage is not visible on the component surface.

Moisture Sensitivity Level chart

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

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. Presently, there are seven categories of moisture sensitivity. It is not surprising that 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.

Moisture Sensitivity level Bake time consideration

When the 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 Table in the next slide re-baking before reflow.

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. 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.

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.

Moisture Sensitivity level Bake time consideration

General Considerations for Baking

The pre-baking and post-baking steps in the MSD component baking can be classified as two different types of baking. 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.

High-Temperature Carriers:- Unless otherwise indicated by the manufacturer, moisture sensitivity level (MSL) components shipped in high-temperature carriers (e.g., high-temperature trays) can be baked at 125°C.
Low-Temperature Carriers:-moisture sensitivity level (MSL) Components shipped in low-temperature carriers (e.g., tubes, low-temperature trays, tape, and reel) may not be baked in the carriers at any temperature higher than 40°C.

If a higher bake temperature is required, moisture sensitivity level (MSL) components must be removed from the low-temperature carriers to thermally safe carriers, baked, and returned to the low-temperature carriers.

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.

Desiccant:-An absorbent material 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 for the plastic packages not to 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.

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

Handling of Moisture sensitivity level (MSL) Components

Moisture sensitivity levels should be used to avoid moisture-related damage during the reflow soldering process. MSD components should be handled as follows

We must ensure that the bag is sealed correctly after each use and contains its HIC.
Before using the contents, the handler must verify that the HIC indicates an acceptable humidity level.
When accessing the components, the handler should record the date and the period during which the bag was open.
Board assembly must be controlled so that “Floor life” exposure times do not exceed the limits for the specific category level.
Manufacturers must ensure that unused components are immediately re-bagged to limit exposure.
If you have a nitrogen chamber, you can also store partially used bags under low humidity conditions.
When the monitoring log and HIC indicate that exposure time limits have been exceeded, the SMT manufacturer should re-bake the components (at 125° C for 24 hours) to ensure dryness before usage.

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 set-ups and product changeover.

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What is Moisture Sensitivity Level? How is MSL level defined!