Title page for ETD etd-08162002-132705

Type of Document Master's Thesis
Author Stinson-Bagby, Kelly Lucile
URN etd-08162002-132705
Title Microstructural Evolution in Thermally Cycled Large-Area Lead and Lead-Free Solder Joints
Degree Master of Science
Department Materials Science and Engineering
Advisory Committee
Advisor Name Title
Lu, Guo-Quan Committee Chair
Reynolds, William T. Jr. Committee Member
van Wyk, Jacobus Daniel Committee Member
  • Microstructural Evolution
  • Thermal Aging
  • Lead-Free Solder
  • Reliability
  • Large-Area Solder Bond
  • Thermal Cycling
  • Die Attach
Date of Defense 2002-06-07
Availability unrestricted
Currently, there are two major driving forces for considering alternative materials to lead-

based products, specifically interconnections, in electronics applications, including the

impending legislation or regulations which may tax, restrict, or eliminate the use of lead

and the trend toward advanced interconnection technology, which may challenge the

limits of present soldering technology. The reliability of solder joints is a concern

because fracture failures in solder joints accounts for 70% of failures in electronic

components. Lead-free solders are being investigated as replacements for lead solders

currently used in electronics. Thermo-mechanical properties describe the stresses

accumulated due to thermal fatigue as a result of CTE mismatch within the system. By

understanding the failure mechanisms related to lead-free solders, the application of lead-

free solders could be more strategically designed for specific applications.

The objective of this thesis is to observe microstructural change in large-area solder joints

caused by thermal cycling and relate these changes to reliability issues in large-area lead

and lead-free solder constructed semiconductor power devices. This study focused on the

microstructural changes within the solder alloy of a large-area solder joint under thermal

cycling conditions. Two major primary observations were made from this research, they

are: 1) due to a combination of testing conditions and material properties, the lead-free

solders, Sn/3.5Ag and Sn/Ag/0.7Cu, sustained the most severe damage as compared to

Sn/37Pb, and 2) due to elevated stresses at the solder/substrate interface in a simulated

power semiconductor device sample damage was found to be most severe.

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