Toray Industries has developed the STF-2000, a photosensitive polyimide solution that enables high-aspect-ratio fine patterning with 30-micrometer line widths in films up to 200 micrometers thick.

This breakthrough came from applying advanced high-sensitivity negative-tone formulation and proprietary photoresist design technology, which controls curing stress.

STF-2000 photosensitive polyimide solution. (Source: Toray)

STF-2000 thick-film processing example. (Source: Toray)

High-performing and sustainable

STF-2000 retains the inherent advantages of a polyimide structure. These include excellent resistance to heat and chemicals, mechanical strength, insulation, and X-ray durability. At the same time, it enables fine microfabrication with aspect ratios of up to 7.

Sustainability is also in the engineering of STF-2000. Toray formulated STF-2000 without PFAS and adopted an alkaline development process that avoids organic solvents. The new material is free of N-Methyl-2-pyrrolidone (NMP) and per- and polyfluoroalkyl substances (PFAS), helping to shrink the environmental footprints of electronic components, micro-electromechanical systems (MEMS) devices, and other applications.

Thick film sheet version available

While the standard formulation of this material is as a solution, Toray is developing a thick-film sheet version. Customer evaluations are underway with a view to commercialization during fiscal 2025.

Examples of thick film and high aspect ratio processing. This photosensitive polyimide material can form various patterns using a standard exposure system with an h-line process. (Source: Toray)

STF-2000 has overcome four key challenges for thick-film photosensitive materials, including deformation and cracking, incomplete ultraviolet curing, inadequate development, and foreign particles and interlayer delamination.

Thick film for electronics industry

Applying the new material to form thick films could enhance insulation of electronic components and support high-aspect-ratio wiring. In structural material applications, it will offer engineers greater design flexibility for microstructures using photolithography so they can develop more advanced MEMS devices.

The material will simplify manufacturing by forming thick-film patterns through a single coating, exposure, and development step, thus boosting productivity and helping cut process costs.

This material also delivers high-resolution patterning with line/space ratios of 4 micrometers or less in the 10-30 micrometer film thickness range traditionally served by conventional polyimides.