A study on effect of wafer bow in wafer-level BCB cap transfer packaging

This paper investigates the effects of wafer bow of Si carrier wafer to achieve high-yield BCB cap transfer in wafer-scale packaging. BCB caps are built-up on Si carrier wafer and then they are bonded and transferred to a target wafer. The height of BCB cap is 25 mu m and the thickness of Si carrier wafer is 380 mu m. Through several experiments, it is found that BCB cap transfer rate is mainly dependent on wafer bow of Si carrier wafer rather than that of the target wafer due to relatively large thickness of BCB caps. Therefore, Si carrier wafer bow with the BCB layers is investigated as a function of temperature. It is to figure out the effect of the wafer bow at certain temperature and applying pressure on BCB cap transfer rate. Through the study, it is found that zero wafer bow is very important for the cap transfer. Hence, aluminum metal layer is introduced to compensate the existing wafer bow of the Si carrier wafer.