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What is MSL (moisture sensitivity level)?

A rating of how readily a surface-mount part absorbs moisture, defined by JEDEC's J-STD-020. It sets the floor life allowed between opening the moisture barrier bag and reflow: 168 hours at or below 30 °C/60% RH for MSL 3. Parts past their floor life are baked dry before mounting.

Japanese name: MSL(吸湿感度レベル)

MSL (moisture sensitivity level) appears in 3 practice questions across 2 topics, including Packaging and assembly, How to read datasheets.

Field: How to read datasheets

Try it: questions about MSL (moisture sensitivity level)

Which is the correct handling of a surface-mount part marked MSL 3 (moisture sensitivity level 3)?

  1. AAfter opening, reflow within 168 hours at 30 °C/60%RH or less; if exceeded, bake before mounting
  2. BThe number 3 means the number of times reflow soldering may be performed is limited to a maximum of three
  3. CIt is a part little affected by moisture absorption, so after the moisture barrier bag is opened it can be stored and mounted without regard to time limits
Show answer and explanation

Answer: A. After opening, reflow within 168 hours at 30 °C/60%RH or less; if exceeded, bake before mounting

MSL is a moisture sensitivity classification defined in a JEDEC standard (J-STD-020) that indicates the time allowed between opening the moisture barrier bag and reflow (floor life). For MSL 3, it is 168 hours (one week) at 30 °C/60%RH or less. If a part is heated in reflow after absorbing moisture, the internal moisture vaporizes suddenly and the package can crack or delaminate (the popcorn effect), so parts past their limit are dried by baking at 125 °C or similar. Only MSL 1 can be handled without a time limit, and higher numbers require stricter control.

MSL (moisture sensitivity level) in the explanations

Questions that mention MSL (moisture sensitivity level) (3)

  1. Which is the correct handling of a surface-mount part marked MSL 3 (moisture sensitivity level 3)?
  2. For surface-mount packages, which moisture-related rating specifies, among other things, how long they may be left after opening the moisture-proof packing before reflow?
  3. In reflow with lead-free solder (Sn-Ag-Cu), which is closest to the peak temperature that parts experience?

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