Research on the mechanism of thermal fatigue in near-eutectic Pb-Sn solders

Conference · Sun Jan 01 00:00:00 EST 1989

OSTI ID:6238958

Morris, Jr., J. W.; Grivas, D.; Tribula, D.; Summers, T.; Frear, D.

This paper discusses the microstructures of solder joints and the mechanisms of thermal fatigue, which is an important source of failure in electronic devices. The solder joints studied were near-eutectic Pb--Sn solder contacts on copper. The microstructure of the joints is described. While the fatigue life of near-eutectic solder joints is strongly dependent on the operating conditions and on the microstructure of the joint, the metallurgical mechanisms of failure are surprisingly constant. When the cyclic load is in shear at temperatures above room temperature the shear strain is inhomogeneous, and induces a rapid coarsening of the eutectic microstructure that concentrates the deformation in well-defined bands parallel to the joint interface. Fatigue cracks propagate along the Sn--Sn grain boundaries and join across the Pb-rich regions to cause ultimate failure. The failure occurs through the bulk solder unless the joint is so thin that the intermetallic layer at the interface is a significant fraction of the joint thickness, in which case failure may be accelerated by cracking through the intermetallic layer. The coarsening and subsequent failure is influenced more strongly by the number of thermal cycles than by the time of exposure to high temperature, at least for hold times up to one hour. Thermal fatigue in tension does not cause well-defined coarsened bands, but often leads to rapid failure through cracking of the brittle intermetallic layer. Implications are drawn for the design of accelerated fatigue tests and the development of new solders with exceptional fatigue resistance. 28 refs., 21 figs.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 6238958
• Report Number(s): LBL-26565; CONF-8903118-1; ON: DE89011430
• Resource Relation: Conference: 13. Department of Navy annual electronics manufacturing seminar, China Lake, CA, USA, 2 Mar 1989; Other Information: Portions of this document are illegible in microfiche products
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
LEAD
THERMAL FATIGUE
SOLDERED JOINTS
TIN
CRACK PROPAGATION
EMBRITTLEMENT
EUTECTICS
GRAIN BOUNDARIES
GRAIN SIZE
MICROSTRUCTURE
SHEAR
CRYSTAL STRUCTURE
ELEMENTS
FATIGUE
JOINTS
MECHANICAL PROPERTIES
METALS
SIZE
360103* - Metals & Alloys- Mechanical Properties
360102 - Metals & Alloys- Structure & Phase Studies
360101 - Metals & Alloys- Preparation & Fabrication