Encapsulating and underfilling materials

Adhesives developed to increase the reliability of BGA, flip-chip, CSP components. The components are attached to the panel, thus reducing the mechanical stress on the solder joints.
Among the underfill materials, we distinguish panel-level (for encapsulated BGA components) and component-level (for unencapsulated Flip Chip components) underfill materials.
The most common are the capillary-flow materials, which after soldering are dispensed in an L-shape next to the component, and from there the capillary effect forces the adhesive to flow under the part, filling the space between the soldering balls. In addition, the so-called “Fluxing Underfill” materials are also available. When using this type of material, we do not apply solder paste under the BGA components, but instead add the underfiller material combined with the flux to the panel. Place the component in this. During soldering, it acts as a flux, promotes the fusion of the molten solder balls and the soldering surface, and then hardens after reflow. 
Newer capillary flow materials do not require preheating of the panel, so the process can be simpler and safer.
For high-reliability electronics, materials with a high Tg (glass transition temperature) and low coefficient of thermal expansion provide the best solution.
For portable equipment, repairability may arise as a requirement. This can also be solved with underfill materials that allow rework.