ANTI-TOMBSTONING LEAD FREE ALLOYS FOR SURFACE MOUNT REFLOW SOLDERING
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United States of America Patent
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app pub date -
Oct 8, 2009
filing date -
Nov 6, 2003
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Abandoned
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Abstract
A lead-free solder alloy composition comprising tin, silver and copper, and a process for reflow soldering for minimizing tombstoning frequency are disclosed. In one particular exemplary embodiment, the lead-free Sn—Ag—Cu solder alloys for minimizing the tombstoning effect of the present disclosure display high mass fraction during melting and prolonged melting as shown by a widened DSC peaks, that allows for a balanced surface tension on both ends of the chip component to develop. In accordance with further aspects of this exemplary embodiment, the alloys display a mass fraction of solid during melting greater than 20% and a DSC peak width greater than 8° C. using a 5° C./min scan rate. In accordance with further aspects of this exemplary embodiment, the alloy comprises on a weight basis Ag 1-4.5%, Cu 0.3-1% balanced with Sn.
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