Advanced Technology Symposium Conference Proceedings


COMPARISON OF MICROSTRUCTURES IN SAC305 AND SAC405 SOLDER JOINTS AND THE INFLUENCE OF SURFACE FINISH

Authors: Daryl Santos, et al.
Company: SUNY at Binghamton
Date Published: 6/11/2002   Conference: Advanced Technology Symposium


Abstract: One of the primary challenges in replacing traditional Pb-bearing solders with Pb-free are the need to ensure highly reliable solder joints. The microstructure of the solder alloy has a great influence on the mechanical properties of the joint, which in turn affects the reliability of the solder joint. Though various Pb-free alloys are in use (and/or being studied), compositions in the Sn-Ag-Cu ternary system are gaining wide acceptance as a preferred replacement for the conventional Pb-bearing alloys.

The weakest links in the case of Pb-free solders are commonly the interfacial intermetallic layers. Generally, the nature and composition of the intermetallic layers depend on the metallurgy of solder alloy, lead metallization and the pad surface finish. The primary goal of this study is to investigate and characterize any microstructural differences between solder joints formed by the Sn96.5Ag3.0Cu0.5 (SAC305) and Sn95.5Ag4.0Cu0.5 (SAC405) solder alloys.

The investigations include study of solder joints of selected surface mount components covering a range of lead metallizations in combination with different board surface finishes. To establish a baseline picture of the microstructural details for the surface mount chip resistors, the selected components are examined in an as-built condition without any subsequent thermal exposure. The current study employs a combination of reflected light optical microscopy, scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDX).

Keywords: Pb-free, Reliability, SAC Alloys, Intermetallics.



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