Evaluation of commercially available, thick, photosensitive filmsas a stress compensation layer for wafer level packaging

摘要

Commercially available, photosensitive dielectrics for use as abump encapsulation or “stress compensation layer” (SCL) forwafer level chip-scale packaging (WL-CSP) were evaluated. Four materialswere identified as potential SCL's. Filled and unfilled photosensitivematerials were evaluated. To be successful as a SCL in WL-CSP, thecommercially available material must be at least 125 μm thick, bephotosensitive, have 1:1 via and saw street resolution, have a totalprocess time of less than 4 hours, have a cure process that does noteffect the under-bump metallurgy, adhere to underlying passivation, andhave a radius of curvature greater than 1.25 m. One commerciallyavailable unfilled photosensitive material had a glass transitiontemperature of 285° C, a CTE of 55 ppm/° C, and a E of 2.5 Gpa.Since the company supplying this material had significant experience inthick, photosensitive film development and processing, they hadexcellent potential as a partner for evaluation. Another unfilled,photosensitive material supplied for this study had a glass transitiontemperature of 330° C, a CTE of 80 ppm/° C, and an elastic modulusof 1.0 GPa. A filled, photosensitive material evaluated had a glasstransition temperature of 130-150° C, a CTE of 45 ppm/° C, and anelongation at break of 2.5%. Of the four materials evaluated, all typesof materials showed potential