Can SnPb BGA's be reflowed reliably using SAC305 solder paste?

First, make sure that 63/37 BGA can withstand higher reflow temperature of of lead free SAC305

GSx

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You as, "What data is available showing the long term reliability of the intermetallics of the solder joints?"

Alloy||Microstructure Sn-Pb||Lamella or globules Sn-Cu||Sn-matrix, Cu6Sn5 needles or globules Sn-Cu-Sb||Sn-matrix, cuboids of SbSn and Cu6Sn5 needles or globules Sn-Cu-Ag||Sn-matrix, Cu6Sn5 needles or globules and Ag3Sn needles Sn-Ag||Sn-matrix, coarse Ag3Sn needles ["Microstructure Behavior of Lead-Free Solder Joints" B. Partee, SMTA Boston, 2001]

Certainly, an assessment of the long-term reliability of lead contaminated SAC solder connections is unrealistic, because of the short period SAC has been in use, much less lead contaminated SAC. Several studies have been made on lead contaminated lead-free solder connections. * Dynamics of Lead Contaminated Solder Joint Failure aimsolder.com/techarticles/Lead%20Contamination%20in%20Lead-Free%20Electronics%20Assembly.pdf * "Evaluation of Nickel/Palladium/Gold-Finished Surface-Mount Integrated Circuits (July 2001)" focus.ti.com/quality/docs/gencontent.tsp?templateId=5909&navigationId=11219&path=templatedata/cm/ecoinfo/data/leadfree_appnotes * Look for a 2004 JGPP lead-free study

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