CONTROLLING MOISTURE-SENSITIVE DEVICES (MSDS) FOR DOUBLE-SIDED REFLOW APPLICATIONS

摘要

Moisture-sensitive devices are commonly used in the industry for many different applications. These components require special handling procedures that must conform to IPC/JEDEC standard J-STD-033 in order to prevent them from absorbing too much moisture prior to reflow. Otherwise they might cause a failure at test or even worse, a latent defect that will cause an early failure in the field. The guidelines of J-STD-033 are very challenging to implement using a manual tracking system. With the advent of double-sided reflow applications, some design limitations can force the use of moisture-sensitive devices on both sides of the board. It is then necessary to monitor not only the components that are placed during second pass prior to second reflow but also the components that were placed during first pass since they continue to absorb moisture between first and second pass. What was already very challenging can become almost impossible to do using a manual tracking system. This paper explains how this issue was solved by the design and implementation of an automatic tracking system for moisture-sensitive devices during first and second pass. The foremost objective of the system is to avoid processing components that have exceeded their allowable limit through the reflow process during first and second pass. This is achieved by automatically tracking each reel or stack of trays from the time they are removed from their original dry bag until all parts are placed prior to reflow and also by tracking the first pass boards until they go through the process in second pass. The automatic system made this possible while maintaining an efficient operation by providing real-time status of the materials and advanced warnings of expiration for decision making.