Baking Moisture Sensitive Devices

A moisture sensitive device is defined as any non-hermetic SMD package that is subjected to solder reflow process during PCB assembly.  Based on moisture sensitivity, devices could be classified from level 1 to level 6, with 6 being the most moisture sensitive level.  The packaging, handling, and repacking of moisture sensitive components requires steps derived from IPC/JEDEC J-STD-033C dated April 2018, “Joint IPC/JEDEC Standard for Handling, Packing, Shipping, and Use of Moisture/Reflow Sensitive Surface Mount Devices.”
•     Moisture Barrier Bags, (MBB) meet JEDEC J-STD-033C (excluding MIL-PRF-81705), requirements for flexibility, ESD protection, mechanical strength, and puncture resistance.  The bags are heat sealable.  The Water Vapor Transmission Rate (WVTR) shall be ≤0.002 gm/100 in2 in 24 hrs. at 40°C after flex testing per condition ‘‘E’’ASTM F 392.  The WVTR is measured using ASTM F 1249.
•     Desiccant materials meet MIL-D-3464, TYPE II. Desiccant is dustless, noncorrosive, and absorbent to amounts specified in the standard.  Desiccant is packaged in moisture permeable bags or pouches.
•     Humidity Indicator Cards, (HIC) are placed inside the moisture barrier bag to serve as an aid in determining the content’s exposure level to moisture.  The humidity indicator card must comply with the JEDEC J-STD-033C.  At a minimum, the HIC shall have three (3) color spots with sensitivity values of 5%, 10% RH and 60% RH.
•     Shelf Life: The calculated shelf life for dry packed SMD packages is a minimum of 12 months from the bag seal date when stored in a non-condensing atmospheric environment of <40°C/90% RH.
•     Floor Life is the allowable time-period, after removal from a moisture barrier bag and before the solder reflow process, for a moisture sensitive device to be exposed to a factory ambient temperature not exceeding 30°C and 60%RH.  The floor life clock shall be stopped/paused while parts that arrive at OX3 in dry-pack condition are being processed.
•     Manufacturer’s Exposure Time (MET) is the maximum time after baking that the component manufacturer requires to process components prior to bag seal.  It also includes the maximum time allowed at the distributor for having the bag open to split out smaller shipments.  When parts come in for baking, OX3 bakes them to allow for a maximum total of 24-hour MET.
The recommended pack quantity for dry packed Plastic Surface Mount Components, PSMCs, is five tubes per bag or one tray plus cover per bag, or one reel per bag.
Components have been exposed to a level of moisture beyond that recommended if the moisture barrier bag is found to have holes, tears or punctures that could expose the contents, if there is no humidity indicator card inside the bag, or if the 5% dot on the humidity indicator card is pink and the 10% dot is not blue.
Parts need to be re-baked as per OX3’s “Work Instruction for Baking,” OX3.5 WI-079.  In such cases, a customer Disposition Form must be initiated.  If the parts are adequately protected as evidenced by the indicator card, then the moisture barrier bag should be resealed as soon as possible to minimize exposure time of components.  The cumulative out-of-bag time for such components shall not exceed 30 minutes.
The “outside of bag time” shall be monitored by stamping the bag with “Date/Time Opened” and “Date/Time Sealed.”  In certain cases where the bag will be opened multiple times during processing, “Exposure Time Form,” OX3.5-FM-097 shall be used.  If the components have been processed, inspected and dry-packed within one hour, the floor life clock will pause/stop.  If the exposure is greater than one hour, then:
i.    For moisture sensitivity levels 2-4, with out-of-bag exposure not greater than 12 hours, a minimum desiccating period of 5x the exposure time is required to dry the SMD packages enough to reset the floor life clock.
ii.   For moisture sensitivity levels 5-5a, with an out-of-bag exposure not greater than 8 hours, a minimum desiccating period of 10x the exposure time is required to dry the SMD packages enough to reset the floor life clock.
iii.  The above requirement does not apply to the parts that have been baked by OX3 before packaging.
Finished parts are readied for shipment in a moisture barrier bag with the correct number of desiccants as specified in “Desiccant Units Table,” OX3.5WI-080, and a humidity-indicator card.  While sealing bag, care should be taken not to evacuate the bag completely, since this will reduce the effectiveness of the desiccant and possibly damage the components.
The desiccant container shall be immediately resealed after each use.  A humidity indicator card shall be placed inside before resealing, if not already present.  If during subsequent reopening of container, the indicator card reads the moisture content to be higher than 10%, the desiccants in the container must be scrapped.
To calculate the number of Desiccant Units required per bag, consult the formula provided in “Desiccant Units Table,” OX3.5 WI-80.
Baking Moisture Sensitive Devices

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