Low Stress and Low Temperature Curable Photosensitive Polyimide

Low stress / low temperature curable photosensitive polyimide (PSPI) with excellent reliability during thermal cycle (TC) has been developed for a quite some time. The effect of residual stress concerning PSPI on copper-PSPI inter-connect structure was examined by Finite Element Method (FEM), and it became evident that the crack has tendency to appear at the top corner between copper and PSPI, where highest stress lay during the cooling process of TC test. Low stress PSPI is one of the candidates to reduce residual stress on copper-PSPI inter-connect structure, and indeed, no crack was found after FEM and TC test. Through a series of tests mentioned above, we came to realize that an introduction of soft segment into polyimide backbone of PSPI is the key factor to create a robust low stress PSPI. In addition of creating a robust low stress / low temperature curable PSPI, further research was conducted to improve the copper compatibility of PSPI through grasping the ways of controlling the oxidation of copper.