Patterning of wafer level applied non-conductive adhesives (NCAs) for camera image sensor (CIS) modules

In this study, wafer level NCA patterning processes for CIS modules have been demonstrated and the effects of whole processes on NCAs were also investigated. At first, NCA solution was directly coated on a bumped wafer with Cu passivation on an image sensing area. Cu was sputtered on a NCA coated wafer, and then sputtered Cu layer was patterned using a photoresist lithography method. Subsequent NCA patterning and descumming were performed using spray etching of NCAs and reactive ion etching (RIE) as a descumming method. Finally, Cu mask on NCA was removed using a ferric chloride solution. At this stage, patterned NCAs on CIS wafers were completed. And then wafers with patterned NCAs were singulated into individual dies. To investigate the effects of the preceding processes on NCAs, degree of cure and chemical structure of NCA were measured using FT-IR during each processes. According to the results, NCAs have no dimensional change and chemical structural change during the whole preceding processes. Finally, singulated chips with patterned NCAs were assembled on a punched FPCB using a thermo-compression bonding method. These flip chip assembly showed stable bump contact resistances of 3∼5 mΩ/bump. The reliabilities of flip chip assemblies using NCA patterning process were evaluated in terms of thermal cycling, high temperature/humidity, and high temperature storage test and compared with those of conventional NCA flip chip assemblies. As a result, there was no difference of reliabilities among wafer level applied and conventional NCA flip chip assemblies.