SMTA International Conference Proceedings


THE EFFECTS OF COPPER CONTENT ON THE RELIABILITY OF Sn-Ag BASED BUMP ALLOYS IN FLIP CHIP APPLICATIONS

Author: Shing Yeh
Company: Delphi Delco Electronics
Date Published: 9/22/2002   Conference: SMTA International


Abstract: This paper investigates flip chip reliability for near eutectic SnAgCu bump as a function of copper concentration. Both reflow experiments and DSC analysis were used to determine the maximum amount of copper that could be added to the eutectic SnAg alloy without impacting its reflow characteristics. Based on the results, Sn-3.5Ag, Sn-3.5Ag-1.0Cu, Sn-3.4Ag-2.0Cu, and Sn-3.3Ag-4.0Cu alloys were selected for further evaluation in wafer bumping, flip chip assembly, and reliability tests.

Excellent results were observed in wafer bump fabrication and assembly of die to various types of substrates for all four alloys given a single set of process parameters optimized for the melting temperature range of eutectic SnAgCu alloy. A series of reliability tests, including thermal cycling, HTS (High Temperature Storage), and HTOL (High Temperature Operating Life) tests, were conducted with these near eutectic SnAgCu bumps to determine the impact of copper concentration on flip chip reliability.

The copper concentration in the SnAgCu alloys was found to have a significant impact on the reliability of the flip chip bumps, particularly when diffusion related failure mechanisms were involved. Bump reliability increased substantially with increasing copper concentration in HTOL and HTS tests. However, the thermal fatigue lives of the SnAgCu bumps were not sensitive to copper concentration.

Key words: Pb-free, SnAgCu, flip chip, reliability, electromigration.



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