What Is Moisture Sensitivity Level(MSL) ?

The Moisture Sensitivity Level (MSL) indicates the time period in which a moisture-sensitive device can be exposed to ambient room MSL is an electronic standard related to the packaging and handling precautions defined in J-STD-020.

Electronic devices (SMD) like QFP, BGA, TSSOP, SOP, Etc. encapsulated with plastic compounds & other organic materials which absorbs moisture from atmospheric Humidity.

SMT components, the entire assembly is placed into reflow ovens where 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 causes dramatic cracking or damaging of the package. Most of this damage is not visible on the component surface.

Moisture Sensitivity Level chart

As IPC/ JEDEC’s standard moisture sensitivity level (MSL) can be defined in the below table. 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, as well as to 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

Moisture sensitivity level bake time that has been exposed only to production ambient conditions of 60% RH for any length of time may be adequately dried by high or low-temperature baking according to Table in next slide for re-bake prior to 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 as well as 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

Upon opening the Moisture Barrier Bag, the floor lifetime starts. If an MBB is opened and the components will not be used within the specified floor life the following table will be used for baking.

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, which details the 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 in the carriers 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 time 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):- A bag designed to limit the transmission of water vapor and used to pack moisture-sensitive devices. For the plastic packages not to absorb moisture, the moisture barrier bag (dry pack bag) must be handled carefully. In order to ensure the safety of your Microsemi devices,

Shelf Life:-The minimum time that a dry-packed moisture-sensitive device can be stored in an unopened Moisture barrier bag (MBB) such that the specified interior bag ambient humidity is not exceeded.

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:- It 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

jedec moisture sensitivity level to avoid the potential for moisture-related damage during the reflow soldering process Handling MSD components must be taken care of as per below-

We must ensure that the bag is properly sealed after each use and that each bag contains its HIC.
Prior to 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, the period of time during which the bag was open.
During board assembly, the “Floor life” exposure times must be controlled to ensure that they do not exceed the limits for the specified category level.
Manufacturers must ensure that unused components are immediately re-bagged to limit exposure.
For those manufacturers that have existing nitrogen chambers, they can also be used to store partially-used bags under low humidity conditions.
When the monitoring log and/or HIC indicates that exposure time limits have been exceeded, the SMT manufacturer should re-bake the components (at 125° C for 24 hours) to ensure dryness prior to usage.

Conclusion – Wrapping it up

As a result, efficient moisture sensitivity level (MSL) control has become important for EMS companies, particularly those working with 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. Moisture Sensitivity Level (MSL) of Microsemi plastic packaging ranges from 3 to 4. If a user plans to store any device beyond the recommended floor life at a temperature or relative humidity above their recommendation, Microsemi recommends the user perform a bake-out before reflow soldering.

Furthermore, markets such as medical, automotive, aerospace and defense, 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 (MSL)?