Surface Mounting SMT LED Indicator Components - App Note

The optical grade materials used in SMT LED components absorb moisture directly from the air. Moisture absorbed in SMT LED components that have been reflow soldered to a pc board is typically on minor concern. However, moisture absorption in SMT LED components prior to reflow soldering is of serious concern. If moisture is absorbed by SMT LED components prior to soldering, the entrapped moisture turns to superheated steam during the solder process. The pressure of this superheated stem fractures the packages of the components causing catastrophic failure. Therefore, it is of vital importance to protect SMT LED components from a absorbing moisture prior to soldering. To protect the SMT LED components from moisture adsorption during shipping and handling, reels for SMT LED components may be packaged in moisture barrier envelopes, as illustrated in Figure 1. Each envelope contains desiccant. To assure the moisture barrier seal, it is important to protect these envelopes from being punctured by sharp objects such as staples. Once opened, SMT LED components should be handled in accordance with the recommendations for their appropriate moisture sensitivity classification. The Joint Industry Standard J-STD-020, Moisture/Reflow Sensitivity Classification for Plastic Integrated Circuit Surface Mount Devices, issued by the EIA/JEDEC JC-14.1 Committee establishes the necessary handling recommendations for each moisture sensitivity classification. For information on the appropriate moisture sensitivity classification of Avago Technologies SMT LED components, please refer to application note AN 5305.