Journal of SMT Article

TERNARY INTERMETALLIC COMPOUND - A REAL THREAT TO BGA SOLDER JOINT RELIABILITY

Authors: Shelgon Yee, Ph. D., et al.
Company: Solectron (Suzhou) Technology
Date Published: 4/1/2004   Volume: 17-2

Abstract: BGA solder joints formed between surfaces with dissimilar metals will lead to the formation of intermetallic compounds (IMC), which can result in serious reliability problems. With gold over nickel on the component side and OSP, silver, tin or HASL finish on the board side, it is common to find rapid growth of nickel-copper-tin ternary intermetallic com-pounds at the component pad interface as copper diffuses from the PCB side to component substrate side. Once this ternary IMC forms a continuous layer, the interface becomes highly susceptible to fracture under stress.

This paper will demonstrate the effect of BGA pad finish on Ni-Cu-Sn ternary IMC growth. Methods for characterizing related solder joint failures and techniques for measuring the strength of the solder joints will also be discussed. Although this phenomenon is still not fully understood, it has proven to be a real threat to BGA solder joint reliability.

Key words: BGA, reliability, intermetallic, ternary IMC, SEM/EDX.



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