Lead Free Requires Increased Moisture Management
Moisture Sensitive Devices (MSDs) are electronic devices encapsulated with plastic compounds and other organic materials. These include PCBs. Moisture from atmospheric humidity will enter these permeable materials by diffusion and preferentially collect at the dissimilar material interfaces.
During solder reflow, the combination of rapid moisture expansion and materials mismatch can result in package cracking and/or delamination of critical interfaces within the package.
These defects are nearly impossible to detect during the PCB assembly and test process. They lead to a number of failure modes that have a negative impact on manufacturing yields and cause early life field failure of the finished electronic products.
The risk of damage during reflow is directly related to the concentration of moisture at the critical interface, which is near the center of the package. The maximum acceptable moisture content and the rate of moisture diffusion vary for each package.
Lead Free Reflow
Reflow temperatures and profiles for lead free soldering increase the risk of damage to components from absorbed moisture. A lead free process will create as much as 3X the Saturated Vapor Pressure as a lead process.
Correspondingly, the Moisture Sensitivity Level (MSL) of the same component (and PCB) increases by as many as two levels when used in a lead free process. The result is shorter floor life for components and PCBs. Parts that had unlimited floor life before lead free are now “moisture sensitive” and must be managed. The SMTA MSD Council has cited even chip resistors and capacitors as potentially problematic.
Europe and America
Earlier and stricter RoHS legislation in Europe is one significant reason why Moisture Management and MSD Control Procedures are so much more mature than those deployed in most of the US. And also why more advanced solutions to extending component floor life were developed and implemented there first. If virtually overnight, all parts in your shop were MSDs, how would you fare?
Totech offers a range of drying and storage solutions to safeguard your MSDs in accordance with IPC/JEDEC J-Std-033 handling standards. View our product range.