SMTA International Conference Proceedings


SOLDER JOINT RELIABILITY OF Pb-FREE TIN-SILVER-COPPER CERAMIC BALL GRID ARRAY (CBGA) PACKAGES AS A FUNCTION OF COOLING RATE AND SILVER CONTENT

Authors: Richard Coyle, Peter Read, Debra Fleming, Richard Popowich, Iulia Muntele; Robert Kinyanjui, Jonathon Shirey, Mulugeta Abtew, John Manock
Company: Alcatel-Lucent; Sanmina-SCI Corp.
Date Published: 10/24/2010   Conference: SMTA International


Abstract: Accelerated temperature cycling (ATC) testing was used to evaluate the influence of microstructure on the thermal fatigue life of Pb-free ceramic ball grid array (CBGA) solder joints. The two key experimental variables that controlled and defined the initial microstructures were the solder joint cooling rate during printed circuit board (PCB) assembly and the Ag content of the CBGA solder balls. The cooling rates bracketed the range expected for a moderately complex telecom printed circuit assembly (1-3?C/sec). The CBGA components were manufactured with Sn3.0Ag0.5Cu (SAC305) or Sn1.0Ag0.5Cu (SAC105) solder balls. SnPb eutectic test cells were included in the matrix for reliability comparisons and as an experimental control.

The ATC test data and failure analysis results are discussed in terms of the relationship to the evolving microstructure and the resultant mechanical behavior from temperature cycling. The results show the influence of the assembly cooling rate and Ag content on the characteristic thermal fatigue lifetime. However, the magnitude of those effects was reduced significantly when the ATC testing is performed using longer dwell test times. Additionally, the results show that the reliability of SnPb eutectic solder likewise is sensitive to cooling rate and cycling dwell time but the dependencies are different than those for SAC solders.

Key words: CBGA, Pb-free solder, accelerated temperature cycling, cooling rate



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