What Is Moisture Sensitivity Level(MSL) ?

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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 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.

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.

Upon opening the Moisture Barrier Bag, the floor life time 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

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 Life :- 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.

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 non condensing 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 take care 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.

Final Thoughts

As a result, efficient moisture sensitivity level (msl) control has become important for EMS companies, particularly those working with high-reliability products.

Furthermore, markets such as medical, automotive, aerospace and defence, 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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