In order to insure that final product reliability has not been compromised during the manufacturing process, it is critical that PCB assemblers have in place a robust system to track the exposure time of moisture-sensitive components and to apply the proper rules and tables documented in the joint IPC/JEDEC standard J-STD-033: Standard for Handling, Packing, Shipping and Use of Moisture/Reflow Sensitive Surface Mount Devices. The standard and the resulting manufacturing procedures always represem a compromise that must err on the conservative side. This can have a very significant cost and reliability inoact since the baking process that is necessary to restore the floor life has many negative implications. The moisture diffusion phenomenon is very complex and the actual absorpt on/desorption curves are different for every component. The IPC/JEDEC guidelines provide a conservative compromise, based on worse case conditions, while providing rules and tables that are as simple as possible to implemen on the assembly floor. The standard includes many rules and tables to determine the remaining floor life based on the time in dry storage and ambient conditions. These rules are still frequently misunderstood and misapplied on the shop floor. The collective experience in the industry has shown that it is very challenging to track a large number of components and their associated floor life with manual logs and procedures For this reason, many manufacturers have already taken the first step to automate the control of moisture-sensitive components on the manufacturing floor. Once the infrastructure is available it can be very beneficial to take more parameters into account to further optimize the overall process.
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