Studies and Analyses of Moisture Conditioned SMT-Components

One of the most challenging aspects of processing electronic parts is the abundance of influencing factors. These have a significant impact on the quality of the finished product. Particularly the affinity to embed moisture in the plastic matrix can lead to severe damage mechanisms. With a moisture gain of up to 0.5 percent by weight [1] delamination and the so-called “popcorn effect” may occur during reflow soldering [2]. This is due to the explosive vaporization and volume gain the embedded water experiences during the heating process. To prevent these failures the floor time has been established. It specifies the maximum amount of time a Surface Mount Device (SMD) can be exposed to certain conditions (floor life) before failures start to occur. After the floor life ends, time-consuming and costly preconditioning in a warm and dry atmosphere is necessary to restart the floor time. The Moisture Sensitivity Level (MSL) in combination with the JEDEC standard defines the exact conditions and times for preconditioning.The proposed article focuses on modeling cause-effect-relations between influence and target values to create a more efficient way to determine when preconditioning is necessary. A literature review of research papers and industry standards is used to determine the quality defining influence parameters. Transferring these insights into two simulation models, one based on the Fickian diffusion mechanism, the other on the two-stage Fickian diffusion, leads to a promising approach for concluding reversible and irreversible moisture diffusion into the SMD components.An experimental setup is determined using the derived dependence model. The experiments consist of defined loading and drying cycles of different samples of MSL 3 and 4 to quantify the moisture de- and absorbed by the part under defined conditions. Subsequently, several differently moisture-loaded parts are reflow soldered to recreate a variety of failure mechanisms. Which, in turn, are used to verify the critical moisture mass absorbed by the SMD-components