Low-CTE, Strong-Adhesion, and High-Resolution Photosensitive Polyimide Materials for Advanced Packaging Applications: Structure and Properties

The use of traditional photosensitive polyimide (PSPI) insulating materials, which possess high coefficients of thermal expansion (CTE) and poor adhesion to copper, easily causes failure issues in the redistribution layers (RDLs). However, there are some trade-offs in the design of the low-CTE PSPI materials such as the ultraviolet (UV) transmittance of the precursors and the dielectric properties of the films. To overcome the above challenges, an AB2-type fluorinated monoamine (ETFPh-NH2) with a nonplanar steric structure was designed and synthesized, which was then used as an end-capper attached to poly(amic ester) (PAE) with a linear/stiff structure. The PSPI solutions were then developed by using the as-prepared PAE resins, solvents, and other additives. Despite the presence of ETFPh-NH2 with a relatively low molar ratio to the total precursor chains, the transparency of the PAE-4 was notably enhanced, resulting in the achievement of the high-resolution lithographic pattern. Meanwhile, the PI-4 film exhibited low-CTE characteristics (23.65 ppm K–1), and its mechanical and low dielectric properties were enhanced by the microbranched cross-link structure, which was constructed by the reaction of the arylethynyl groups during the imidization process. Furthermore, the adhesion between the PI films and Cu was significantly improved by introducing the aromatic silane (TMS). In short, PI-4, which exhibited high-dimensional stability, strong adhesion with Cu, and photopatternable capabilities, could be a feasible and reliable material for use in advanced packaging. In addition, the developed end-groups modification strategy seems to be an effective way to greatly improve the overall performance of PSPI materials.