Patent ID: 6440836
Filing Date: 2002-08-27
Classification: H01L

Abstract:
A method for forming solder bumps on flip chips comprising the steps of:providing an electronic substrate having a metal bond pad formed on top, said bond pad being embedded in an insulating layer with only a top surface exposed, depositing a ball-limiting-metallurgy (BLM) layer on top of said electronic substrate, coating a first photoresist layer on top of said BLM layer, said first photoresist layer having a first thickness that is sufficiently small such that an exposure accuracy of at least Â±2 &mgr;m is obtained, etching said BLM layer away except an area over said bond pad, coating a second photoresist layer on top of said etched BLM layer, said second photoresist layer having a second thickness that is larger than said first thickness, forming a via opening in said second photoresist layer over said BLM layer and filling with a solder to form a solder bump, and removing said second photoresist layer and reflowing said solder bump into a solder ball.