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The impact of bumping stress on Cu RDL structure

Wafer-level-packaging (WLP) is widely used in consumer products and is directly packaged on wafers. Wafer warpage and internal stress is a big challenge.RDL direct on passivation structure is mainly used for power management device because they have better electrical carrying capability and performance. However, a thick Cu RDL is located in the structure of the passivation layer, which leads to the bumping stress direct to the passivation layer. Bumping stress comes from Cu plating (plating stress), PI curing and solder ball reflow process because of Coefficient of Thermal Expansion mismatch of different material (Silicon, Cu, PI material, Solder ball). The method to reduce the wafer warpage and internal stress and reduce the impact on the reliability of the device during the collision are investigated in the present study.