How to read datasheets
Which is the correct handling of a surface-mount part marked MSL 3 (moisture sensitivity level 3)?
- AAfter opening, reflow within 168 hours at 30 °C/60%RH or less; if exceeded, bake before mounting
- BThe number 3 means the number of times reflow soldering may be performed is limited to a maximum of three
- 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.