Development of Novel Low-Temperature Curable Positive-Tone Photosensitive Dielectric Materials with High Reliability

Novel low-temperature curable positive-tone photosensitive polyimide (posi-PSPI) with high reliability has been developed as dielectric layers for copper redistribution layers (RDLs) in Fan-Out wafer/panel level packages (FOWLP, FOPLP). The posi-PSPI shows high tolerance to thermal cycle test, high temperature storage test and Cu migration test. In order to achieve these properties, we investigated both segments of flexible and rigid molecular skeletons within the base polymer backbone. Through a modification of suitable flexible segment contributed to Cu migration resistance with its assumed characteristics to have better flow coverage of Cu patterns. In addition to segmental modification, we also came to realize that a balance between flexible and rigid segment was an important factor for the stabilization of elongation under freezing temperature and thermal cycle test. Furthermore, we have also investigated an additive within the material such as anti-oxidant. This additive suppressed the voids from generating between Cu and Polyimide, which are the initial cause of delamination. This phenomenon of void formation was due to rapid speed of Cu oxide diffusion during a high temperature storage test. The posi-PSPI offers fine pattern with good sensitivity by photolithographic system. It can also be processed by laser direct imager (LDI) instead of i-line stepper or aligner, and the patterned material made by photolithography can be reworked by organic solvents. In addition, this posi-PSPI showed high adhesion to various substrates, such as Si, Cu, Mold resin, and PI itself. These features certify that this material is suitable for applications of FOWLP/FOPLP.