Methodology to control underfill fillet size, flow-out and bleed in flip chips (FC), chip scale packages (CSP) and ball grid arrays (BGA)

In a method and system for underfilling a gap ( 140 ) disposed between a substrate ( 120 ) and a die ( 110 ), a selective surface ( 152 ) of the substrate ( 120 ) is treated by a plasma source. A matching surface ( 154 ) of the die ( 110 ) may be treated by the plasma source. The treating results in a roughening of the selective surface ( 152 ) and the matching surface ( 154 ). The roughening improves welting of an underfill ( 150 ) on the selective surface ( 152 ) and the matching surface ( 154 ) compared to a non-treated surface. The underfill ( 150 ) is dispensed to substantially fill the gap ( 140 ) disposed between the selective surface ( 152 ) and the matching surface ( 154 ) of the die 110 . The underfill ( 150 ) is substantially contained within the gap ( 140 ) by the wetting, which reduces the backflow and the bleed of the underfill ( 150 ).