Moisture Sensitivity Level Receiving Audit and Dry Bake Containment
Receiving verification of moisture barrier packaging and strict floor life tracking prevent reflow delamination yield losses in surface mount assembly.
Ambient Floor Life
Exposure Duration
Permissible time limits govern the storage of moisture-sensitive electronic components outside of protective sealed packaging. This duration is called the ambient floor life of the device. Once this duration is exceeded, the component must undergo a baking cycle to remove absorbed moisture.
The value varies from a few hours to an indefinite duration depending on the specific sensitivity rating of the part.
Degradation Mechanism
Plastic packages absorb moisture from the surrounding environment when exposed to room temperature and humidity. Ambient floor life decreases when the ambient relative humidity rises above the standard storage baseline of fifty percent. Absorbed moisture vaporizes rapidly during subsequent reflow soldering, which can cause internal package cracking or delamination.
This thermal expansion risk means that exposure time must be kept within strict boundaries. When the protective barrier is breached, the plastic immediately begins to accumulate moisture at a rate determined by the vapor pressure of the surrounding air.
Verification Process
Traceability cards are attached to each reel or tray of parts to track cumulative exposure. Operators record the date and time when the protective barrier bag is first opened. Automated software systems can scan barcode labels to calculate the remaining available time.
If the parts are returned to a low humidity environment, the tracking clock is paused.
Control Threshold
Industry standards such as those from IPC and JEDEC establish standard durations for different device classes. For instance, class three devices typically allow one hundred and sixty eight hours of room exposure. Storage in a dry cabinet or a nitrogen-purged chamber extends the usable life.
If the threshold is exceeded, a thermal bake of eight or twenty four hours is required.