Low-temperature Curable and high Tg Polyimide with a pyrazine-contained unsaturated diamine

Polyimides (PIs) are widely applied in semiconductor industry, serving as stress buffers, passivation layers and interlayer dielectrics in the redistribution layer of wafer level package, for their outstanding comprehensive performance. However, a high curing temperature (>350°C) is required usually for PI precursors (poly amic acid or poly amic ester), which limit the application scope in semiconductor devices. And to avoid the warpage of the device wafer because of the CTE mismatch of the heterostructure in the high-temperature curing process, the novel low-temperature curable polyimide is highly deserved. Herein, a new diamine (4,4'-(pyrazine-2,5-diylbis(ethyne-2,1-diyl))dianiline, short for PRZYDA) with a heteroaromatic skeleton of pyrazine and unsaturated bond was synthesized at first. And after carefully co-polymerization with PMDA, ODA and PRZYDA, the imidization temperature can be successfully reduced to 250 °C because of the existence of the pyrazine ring, comparing with controlled non-additive group. Besides, the low-temperature cured PI films exhibited excellent mechanical properties and thermal stability (tensile strength of 146 MPa, enlongation of 32.4%, modulus of 2.67GPa, CTE of 29.7 ppm/K and T g of 388°C). In a word, this study proves that the introduce of the novel diamine of PRZYDA is a very feasible method to get a low-temperature curable and high T g polyimide, and it also provides a good reference for polyimide in wafer level advanced packaging.