PCBs are moisture sensitive devices.
Advances in IC package design and manufacturing process allows much more components to be mounted in a smaller surface on multi-layer PCBs. But reliability of a finished PCB relies heavily on the proper moisture control beginning from the lamination process. If any trapped moisture are present during the reflow process, delamination, blistering and other defects will occur. But the question is, how far in advance must this be considered?
Proper Prepreg Handling
High humidity condition will cause moisture to be absorbed by the prepreg, especially when an open bag of prepreg is transported from cold storage to the processing area. This change in temperature will cause rapid moisture condensation on the prepreg. Best practice recommends allowing the prepreg to equilibrate to room temperature before the bag is opened. Some prepreg that does not require low temperature storage, can be stored in Eureka's dry cabinet at less than 50%RH until the material is needed for use. For prepregs that requires lower temperature storage can be stored in Eureka's dry cabinet while waiting for it to reach temperature. Assuring all excessive moisture are eliminated while decreasing the amount of harmful baking cycles the board needs to go thru.
Proper PCB Handling
PCBs are typically shipped in vacuum sealed anti-static or Moisture Barrier Bags (MBB) with desiccants and humidity indicator cards (HICs) inside to ensure it's quality. But once the PCBs are removed from the MBB for processing, natural moisture absorption begins. Some PCBs require mounting of devices of both sides. Moisture continues to be absorbed by the PCB while waiting for the second side to be assembled. Depending on the ambient humidity levels and the length of exposure, moisture content could reach critical levels before assembly is completed, leading to higher chances of delamination.
These are examples of the type of moisture related damage to a PCB assembly that can occur if incorrect storage or handling is not followed.
Image sourced from : Bob Willis [email protected] www.Bobwillis.co.uk /https://www.youtube.com/watch?v=pn7P-knw_lg&feature=youtu.be
While baking the boards to remove moisture is an option. However, it comes at the cost of solderability, oxidation and intermetallic growth. Storing the unmounted PCBs in a nitrogen purge system is costly and will not remove the moisture that has been absorbed by the PCB. For the safest and most effective storage and proper handling of PCBs is to store it in Eureka's Ultra Low Humidity Fast Super Dryer.
Eureka's Ultra Low Humidity SMT dry cabinets are safe and effective methods for storing PCB, MSD, contact leads, solders and other moisture sensitive materials used in the electronic manufacturing. Eureka's dry cabinet will provide alternative moisture removal solution to standard baking oven and increase production yields, while producing higher quality and reliability products.
Eureka's SMT dry cabinets does not require nitrogen purge to function and is available in various sizes and moisture control capabilities. Our XDC and SDC series Fast Super Dryer SMT Dry Cabinets provides the most suitable storage environments for PCB and other moisture sensitive material in the production floor. Ensure your production line is protected from harmful moisture and increase the yield & quality of your products with Eureka's ultra low humidity SMT Dry Cabinets today.
For more details and specs about Eureka's products, please click on the links below.