A FEM study on debonding process for BCB cap transfer packaging

This paper presents a FEM analysis of a wafer-level BCB cap transfer packaging process utilizing simple and easy detachment of the carrier wafer. The detachment has been implemented through hydrophobic monolayer coating of Si carrier wafer surface before BCB cap patterning. Razor blade insertion between Si carrier and device wafer is used to separate BCB caps from the carrier wafer to complete the packaging. The behaviour of the Si carrier wafer detachment is investigated through FEM-modelling of the stack of Si carrier wafer and BCB caps. Especially, the hydrophobic monolayer interface is modelled using ANSYS CZM method to include its low surface energy properties. Load-displacement curves are first examined to comprehend the debonding behaviour of Si carrier in view of BCB cap detachment. It is found that fracture at the interface is initiated at low applied force level of tens mN thanks to the monolayer coating and the Si carrier wafer is separated from the BCB cap just after maximum deflection and maximum stress of BCB cap are attained. In addition, it is found that BCB cap deflection is linearly proportional to BCB cap size and maximum stress increases as function of BCB cap size.