Characteristics and potential application of polyimide-core-bump to flip chip

Polyimide core bumps are formed by following these steps: first, forming polyimide cores using photosensitive polyimide, next, metallization on the polyimide cores by sputtering, and finally, patterning the metallized layers. The polyimide core bumps thus prepared have the advantages of larger aspect ratios, and better bump height uniformity without 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 adhering, or other mechanical contact with adhesive.