Highly reliable photoimageable dielectric resins for wafer level CSP redistribution

The use of photoimageable dielectric resins for rewiring of WL-CSP's and passivation is increasing dramatically. Initial material selection for WL-CSP dielectrics was made from passivation materials. High processing temperatures, high shrinkage, difficult processing, poor adhesion, and poor electrical or thermal-cycle reliability are problems often experienced with these materials. A highly reliable epoxy based dielectric resin was designed specifically for use on wafer substrates. Excellent physical properties and extremely low shrinkage were obtained with low temperature cure schedules. Excellent electrical and thermal-mechanical properties gave superb reliability and fine resolution was obtained using alkaline development. This paper will focus on advancements made with regards to photolithography, thermal-mechanical properties, adhesion, and reliability.