T. Nishimori et al., CHARACTERISTICS AND POTENTIAL APPLICATION OF POLYIMIDE-CORE-BUMP TO FLIP-CHIP, IEEE transactions on components, packaging, and manufacturing technology. Part A, 19(1), 1996, pp. 18-23
Polyimide core bumps are formed by following these steps: first, formi
ng polyimide cores using photosensitive polyimide, next, metallization
on the polyimide cores by sputtering, and finally, patterning the met
allized layers. The polyimide core bumps thus prepared have the advant
ages of larger aspect ratios, and better bump height uniformity withou
t conventional levelling process, and larger elasticity compared with
solid metal bumps such as gold or solder. Also various bonding methods
are applicable as solderings, or gold-tin bonding with pressure and a
dhering, or other mechanical contact with adhesive.