Warpage reduction of thin dies by capillary action of underfill materials

The warpage reduction by capillary action is a new approach for the assembly of warped flexible thin silicon dies that do not need external pressure or a die carrier for mounting the die to the substrate. The warpage of the dies is reduced as a result of the capillary pressure of a liquid enclosed in the gap between die and substrate. Previous experiments, carried out with water and glycerol as liquid, showed the functionality of the approach. The aim of this study was the replacement of the mentioned liquids by (no-) flow Underfill. These materials have the advantage that they can cure and remain in the gap when assembly is finished. Three no-flow underfill (NFU) and one flow underfill (FU) were tested in the experiments of this study. A successful warpage reduction could be achieved with one of the NFUs and with the FU. If the two other NFU-Materials were used excessive air inclusions occurred in the gap and inhibited a warpage reduction. The reason of the air inclusions are a subject of further investigations. However, the results have shown that the warpage reduction is also possible with a NFU as liquid.