A STUDY OF THE MECHANISM AND DETERMINATION OF THE ACTIVATION ENERGY FOR DIE PAD UNDER BUMP METAL RESISTANCE INCREASE ON FLIP-CHIP DIE USING SCANNING ACOUSTIC MICROSCOPY AND HIGH TEMPERATURE STORAGE

摘要

Electrical failures were encountered after high temperature storage (HTS) stressing as part of a device qualification. The failure signature was an increase in resistance at input and output circuits. Failure analysis determine that the high resistance was due to voiding in the under bump metallization for the die solder bumps. Various other high temperature studies were conducted to characterize the failure mechanism and determine the activation energy so that reliability predictions could by performed. Initially, continuous monitoring of the increase in resistance was used as the indicator of the progress of the metallurgical degradation of the UBM. It was later determined that Scanning acoustic microscopy imaging could be used to monitor this degradation and could be used in a quantitative way to determine the activation energy. Different UBM metal systems and process variations could be studied quickly without the need for electrical monitoring or electrical testing. This paper presents the methodology and techniques used to develop and implement the scanning acoustic microscopy approach to the reliability studies.