Method for forming solder bumps on flip chips and devices formed

Abstract

The present invention discloses a dual-photoresist method for forming fine-pitched solder bumps on flip chips by utilizing two separate layers of photoresist, i.e., a first thin photoresist layer for patterning the BLM layers on top of the aluminum bonding pads and a second thick photoresist layer for patterning the via openings on top of the BLM layers to supply the necessary thickness required for the solder bumps. The first, thin photoresist layer permits an accurate imaging process to be conducted without focusing problems which are normally associated with thick photoresist layers. As an optional step, the present invention may further utilize a thin layer of non-leachable metal such as Cu or Ni for coating on top of the BLM layer and thus further improving the electrical characteristics of the solder bumps subsequently formed thereon. A majority of the BLM layer is removed with the first, thin photoresist layer and thus, in the final BLM removal process, only a very thin adhesion sublayer of the BLM layer needs to be removed and as a result, ensures a clean removal process without damaging the solder bumps already formed with a fine-pitch.

Dependencies are inferred from the claim text.