Fill Gap
This tool is used to help fill the gaps between the dies or chips on a PCB (printed circuit board). When several dies/chips are placed near each other, it is essential to fill the gap between them before creating an underfill around them. The gap can be filled partially or entirely, depending on the required height.
Chip bodies on one side
Select the chips/dies on one side. When there are multiple stacked dies, it is essential to ensure that all of them are selected.
Chip bodies on other side
Select the chips/dies on other side. When there are multiple stacked dies, it is essential to ensure that all of them are selected.
PCB
Select the PCB body.
Example
Case1: Underfill height = OFF
Case2 : Underfill height = ON