Pan Pacific Symposium Conference Proceedings


Authors: Heather McCormick, Polina Snugovsky, Craig Hamilton, Zohreh Bagheri, and Simin Bagheri
Company: Celestica Inc.
Date Published: 1/31/2007   Conference: Pan Pacific Symposium

Abstract: Although the electronics industry has largely settled on the use of SAC alloys for the assembly of the majority of lead free products, debate continues to exist over which SAC alloy – SAC305 (Sn3.0Ag0.5Cu) or SAC405 (Sn3.8Ag0.7Cu) – to use. The North American industry generally favours SAC405, while the Asian industry favours SAC305. SAC305 has the significant benefit of being less expensive than SAC405 owing to its lower silver content. However, there are lingering questions about whether the reliability of SAC305 is comparable to that of SAC405. Recent studies have concluded that no significant difference exists, but many potential applications were not studied. This paper compares the results of reliability testing of SAC305 and SAC405 in three different cases on a test vehicle representative of a mid-complexity server-type product which included a range of component types from CBGAs to discrete resistors. The first case compares the reliability of pure SAC305 assemblies to pure SAC405 on a variety of surface finishes, including ENIG, ImmAg, ImmSn, Electrolytic Ni/Au and OSP. These assemblies differ from those used in many other studies1-4 in that SAC305 balled area array components were used on assemblies screened with SAC305 paste, and SAC405 balled area array components were used on assemblies screened with SAC405 paste, resulting in pure SAC305 or pure SAC405 systems. Many previous studies have used area array components balled with SAC405, but increasing use of SAC305 by component suppliers for balling area array components means it can no longer be assumed that BGA components will have SAC405 balls. The reliability of these assemblies was determined in 0°C to 100°C thermal cycling. In the second case, a small sub-set of the assemblies, again, either pure SAC305 or pure SAC405 systems, were tested in harsher -55°C to 125°C thermal cycling more representative of a military or aerospace end-use environment. In the third case, the reliability of mixed assemblies created with either SAC305 or SAC405 balled components and tin/lead paste was studied using the 0°C to 100°C thermal cycle to determine if the difference in composition of the component ball affects the reliability of the resulting assembly. Key words: Lead Free, SAC 305, SAC405, Mixed Joints

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