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MSL: MSL is the abbreviation of Moisture
Sensitivity Level, which means the moisture sensitivity level. MSL is proposed
to provide a classification standard for the packaging of moisture-sensitive
SMD components, so that different types of components can be packaged, stored and
handled correctly, and accidents can be avoided during assembly or repair.
Generally, the packaged IC, colloid or
Substrate PCB will absorb moisture in a normal environment, resulting in
"popcorn" (POPCORN) when the IC goes through SMT reflow soldering. Moisture
Sensitivity Level (MSL) is used to define the level of IC in terms of moisture
absorption and shelf life. If the IC exceeds the shelf life, there is no
guarantee that it will not absorb too much moisture and cause POPCORN during
SMT reflow soldering . Therefore, bake the IC beyond the shelf life.
The process of MSL determination is:
(1) Carry out SAT on the good product IC to
confirm that there is no delamination.
(2) Bake the IC to completely remove
moisture.
(3) Humidification according to MSL level.
(4) Pass IR-Reflow 3 times (analog IC
assembly, maintenance dismantling, maintenance and assembly).
(5) SAT inspection for delamination and IC
test function.
If it can pass the above test, it means
that the IC package meets the MSL level.
The classification of MSL has 8 levels, as
follows:
Class 1 - Less than or equal to 30°C/85% RH
Unlimited workshop life
Class 2 - Less than or equal to 30°C/60% RH
One year workshop life
Class 2a - Less than or equal to 30°C/60%
RH Four week workshop life
Class 3 - Less than or equal to 30°C/60% RH
168 hours workshop life
Class 4 - Less than or equal to 30°C/60% RH
72 hours workshop life
Class 5 - Less than or equal to 30°C/60% RH
48 hours workshop life
Class 5a - Less than or equal to 30°C/60%
RH 24 hour workshop life
Class 6 - Less than or equal to 30°C/60% RH
72 hours floor life (for Class 6, components must be baked prior to use and
must be reflowed within the time limit specified on the Moisture Sensitive
Caution Label)
Moisture not only seriously accelerates the
damage of electronic components, but also has a huge impact on the components
during the soldering process. This is because the component soldering on the
product production line is performed at high temperature by wave soldering or
reflow soldering and automatically by the soldering equipment. Completed. When
the components are fixed to the PCB board, the rapid heating of reflow
soldering will create pressure inside the components. Due to the different
coefficient of thermal expansion (CTE) rates of different package structure
materials, it may cause stress that the component package cannot bear.
When the components are exposed to reflow
soldering, the moisture inside the SMD components can generate enough vapor
pressure to damage or destroy the components due to the rising temperature
environment. Common conditions include plastic separation (delamination) from
the inside of the chip or lead frame, gold wire solder damage, chip damage, and
cracks inside the component (not visible on the component surface). In some
extreme cases, cracks can extend to the surface of the component, and in severe
cases, the component bulges and pops (called the "popcorn" effect).
Although a small amount of moisture is acceptable at 180°C to 200°C during
reflow soldering operations, any presence of humidity in lead-free processes in
the range of 230°C to 260°C can form enough to cause damage to the package.
Small explosions (popcorn-like) or layers of material. Therefore, it is
necessary to choose wise packaging materials, carefully control the assembly
environment, and adopt measures such as sealing packaging and placing desiccant
during transportation. In fact, foreign countries often use humidity tracking
systems equipped with radio frequency tags, local control units and special
software to display and control the humidity in packaging, testing lines,
transportation/operation and assembly operations in real time.
