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Low Temperature Soldering: Reflow Enhanced Mechanical Reliability



Low Temperature Soldering: Reflow Enhanced Mechanical Reliability
In this work, we further discuss solderability and mechanical reliability of a novel low temperature proprietary alloy (generically called as X46).
Materials Tech

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Authored By:


Morgana Ribas, Ph.D., Bhaskar Vangapandu, Raghu Raj Rangaraju, Suresh Telu, Ph.D., Laxminarayana Pai, Ramesh Kumar, Vikas Patil, H. V. Ramakrishna, Ph.D., Traian Cucu, Ph.D., Siuli Sarkar, Ph.D.
Alpha Assembly Solutions, a MacDermid Performance Solutions Business
Bangalore, India

Summary


There is a growing interest surrounding use of Sn-Bi solder alloys for lowering reflow soldering temperature. Among the many benefits enabled by that are: Reduced dynamic warpage, more complex assemblies, reduced energy costs and increased production yields. Recently, low temperature solder alloys with micro-additives have been introduced as an alternative for replacing Sn-Ag-Cu solders while maintaining its mechanical (drop) shock performance. In this work, we further discuss solderability and mechanical reliability of a novel low temperature proprietary alloy (generically called as X46). Its drop shock performance evaluation is extended to include the effect of various reflow profiles, including the effect of time above liquidus (TAL) and peak reflow temperatures. Analysis of soldering performance, including voids measurements, and failure analysis are also included in the discussion. Based on these results, the following reflow conditions are recommended: (i) For BGA, peak temperature of 190-200oC (3oC) and TAL between 30 and 90s, (ii) For the LGA, 180-200oC (3oC) peak temperature and TAL between 30 and 90s.

Conclusions


In this work, we investigated the effect of various reflow profiles on solderability and solder joint mechanical shock reliability. Its key observations are:
  • Extended TAL of 120s results in more voids in BGA256 and does not pass IPC RSB test after 4 hrs conditioning.
  • LGA84 can be reflowed at 180, 190 or 200oC peak temperature using 30 to 120s TAL, without degradation of mechanical shock performance.
  • Mixed failure mode was observed for BGA reflowed at 180 and 200oC, but all BGA reflowed at 190oC showed cracks through the IMC after the drop shock test.
  • BGA84 can be reflowed at 190 or 200oC peak temperature using 30 to 120s TAL (or 30 to 90s TAL in case of 200oC peak), without degradation of mechanical shock performance.


Initially Published in the SMTA Proceedings

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