Moisture Sensitivity Level relates to the packaging and handling precautions for some semiconductors. The MSL is an electronic

Electronics

Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

 standard for the time period in which a moisture sensitive device can be exposed to ambient room conditions (approximately 30°C/60%RH).

Increasingly, semiconductors have been manufactured in smaller sizes. Components such as thin fine-pitch devices and ball grid array

Ball grid array

A ball grid array is a type of surface-mount packaging used for integrated circuits.- Description :The BGA is descended from the pin grid array , which is a package with one face covered with pins in a grid pattern. These pins conduct electrical signals from the integrated circuit to the printed...

s could be damaged during SMT

Surface-mount technology

Surface mount technology is a method for constructing electronic circuits in which the components are mounted directly onto the surface of printed circuit boards . An electronic device so made is called a surface mount device...

 reflow when moisture trapped inside the component expands.

The expansion of trapped moisture can result in internal separation (delamination

Delamination

Delamination is a mode of failure for composite materials. Modes of failure are also known as 'failure mechanisms'. In laminated materials, repeated cyclic stresses, impact, and so on can cause layers to separate, forming a mica-like structure of separate layers, with significant loss of mechanical...

) of the plastic from the die or lead-frame, wire bond damage, die damage, and internal cracks. Most of this damage is not visible on the component surface. In extreme cases, cracks will extend to the component surface. In the most severe cases, the component will bulge and pop. This is known as the "popcorn" effect.

IPC

IPC (electronics)

IPC, the Association Connecting Electronics Industries, is an organization whose aim is to standardize the assembly and production requirements of electronic equipment and assemblies. It was founded in 1957 as the Institute for Printed Circuits...

 (Association Connecting Electronic Industries) created and released IPC-M-109, Moisture-sensitive Component Standards and Guideline Manual.

Moisture sensitive devices are packaged in a moisture barrier antistatic bag

Antistatic bag

An antistatic bag is a bag used for shipping components, which are prone to damage caused by electrostatic discharge.These bags are usually plastic and have a distinctive color . The polyethylene variant may also take the form of foam or bubble wrap, either as sheets or bags...

 with a desiccant

Desiccant

A desiccant is a hygroscopic substance that induces or sustains a state of dryness in its local vicinity in a moderately well-sealed container....

and a moisture indicator card which is sealed.

IPC-M-109 includes seven documents. According to IPC/JEDEC's J-STD-20: Moisture/Reflow Sensitivity Classification for Plastic
Integrated Circuit (IC) SMDs, there are eight levels of moisture sensitivity. Components must be mounted and reflowed within the allowable period of time (floor life out of the bag).

• 'MSL 6 - Mandatory Bake before use
• MSL 5A - 24 hours
• MSL 5 - 48 hours
• MSL 4 - 72 hours
• MSL 3 - 168 hours
• MSL 2A - 4 weeks
• MSL 2 - 1 year
• MSL 1 - Unlimited