SMTA International Conference Proceedings


SOLDERING AND SOLDER JOINT RELIABILITY FOR SELECTED SURFACE FINISHES WITH LEAD FREE SAC305 ALLOY

Authors: George Milad and Don Gudeczauskas
Company: Uyemura International Corporation
Date Published: 10/11/2007   Conference: SMTA International


Abstract: The surface finishes Ni/Au (hereafter referred to ENIG), Ni/Pd/Au (hereafter referred to ENEPIG),Ag (IAg) and direct immersion Au (DIG) were prepared on ball grid array (BGA) circuit boards patterns by electroless/immersion plating methods. Solder balls of Sn37Pb and Sn3.0Ag0.5Cu were attached/soldered. The IMC (Inter metallic compound) formed and its propagation, as a result of artificial ageing (150 degress C for up to 1000 hours) was studied using SEM analysis. Ball pull was also conducted as an indicator of solder joint strength and reliability.

It was also found that the IMC crystal lattice is dependant on solder material and the solder joint reliability is dependant on both the solder material as well as the surface finish. It was found that all four surface finishes would transition well into LF SAC 305 soldering and would produce a reliable solder joint under the experimental conditions investigated.

The surprise finding was that ENEPIG made a particularly high reliability solder joint with SAC305 as compared to the Sn37Pb. The eutectic Sn37Pb solder joint was non-uniform and uneven when formed and got progressively weaker with thermal ageing as the IMC continued to propagate.



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