摘要： The standard pillar bump structure [1-3] is shown in Figure 2. Polyimide Re-passivation (PI) layer is widely used for pillar bump structure due to the increasingly stringent reliability requirements [4-5]. PI layer serves as stress buffer layer which can enhance the structure reliability performance. And PI will be the direct surface contact material to FCBGA molding compound, so the PI surface roughness is a key factor to the adhesion between PI and molding compound. Lower surface roughness will cause delamination between PI and molding compound while higher surface roughness may cause flip chip process issue like back-grinding tape residue due to higher adhesion between PI and back-grinding tape [6-7]. During the pillar bump process, the PI surface roughness is influenced by many plasma steps like gas and so on. In the present paper, plasma process parameters such as gas, process power and process time are studied in order to get the correlation between these process parameters and PI surface roughness result. This correlation can be used to further study the surface roughness with the assembly site required at the assembly process. As depicted in Figure 3, there are distinctions in the diffraction values of Selected Area Diffraction Pattern (SADP) in different process steps (PI Curing, O2 Descum, RF, Etch, Ar Descum). The influence of different gases plasma on PI surface roughness is quite significant, among which O2 plasma has more significant impact than others, which provides guidance for further research of PI surface roughness in FCBGA