Component Reinforcement
Liquid epoxy resins fill the gap between the active surface of a flipped silicon chip and the underlying substrate to secure the assembly. Applying underfill encapsulation distributes mechanical and thermal stresses across the entire surface of the chip, which protects the delicate solder bumps from fracturing during operation. The process is commonly used in high-reliability mobile devices and automotive control units.
Capillary Flow
The liquid resin is dispensed along one or two edges of the package, from where it is drawn into the narrow gap by capillary force. Underfill encapsulation requires a heated substrate to lower the viscosity of the epoxy, ensuring that it flows smoothly around all the solder joints without leaving air pockets. Once the gap is completely filled, the board is placed in an oven to cure the epoxy into a solid, rigid layer.
Stress Redistribution
Curing the resin establishes a coefficient of thermal expansion that matches both the silicon and the substrate, minimizing differential movement during thermal cycles. This redistribution prevents localized shear forces from concentrating on the individual solder bumps.
Inspection Scan
Acoustic microscopy is utilized after the curing cycle to verify that the epoxy is free from voids or delamination. The presence of voids would undermine the mechanical integrity of the reinforcement.
