Underfill provides a strong mechanical bond between the chip and the PCB's connection, protecting the solder joints from mechanical stress. It also helps transfer heat. Underfill softens the mismatch between the coefficient of thermal expansion (CTE) between the chip and the board.

What is underfill used for?

The use of underfill enables structural coupling of the chip and substrate, effectively decreasing the shear stress and thus lowering the applied strain on the solder joints [35]. The key properties of underfill materials are detailed in Table 2.23. CTE: Coefficient of thermal expansion.

What is underfill in BGA?

Introduction. Underfill technique is used under the BGA to strengthen solder joints, and reinforce the product's resistance against vibration and thermal shock.