Microstructural observations of the Sn-Pb solder/Cu system and thermal fatigue of the solder joint

Technical Report · Mon Jun 01 04:00:00 EDT 1987

OSTI ID:6114447

Frear, D R

This study was performed in order to understand the microstructural mechanisms that lead to solder joint failures in thermal fatigue. The solders studied were 5Sn-95Pb and 60Sn-40Pb joined to Cu. The precipitation process of ..beta..-Sn in 5Sn-95Pb was fully characterized. On fast cooling from single phase ..cap alpha..-Pb the Sn precipitates homogeneously. On slow cooling the precipitation process is cellular. The 60Sn-40Pb had a two phase microstructure. The Sn-rich phase was interconnected and polygranular. Both phases, and Sn grains, coarsened with time at 125/sup 0/C. Coarsened 60Sn-40Pb microstructure was deleterious to the mechanical properties. Failures initiated and propagated through interfacial intermetallics only at extremely fast strain rates. Interfacial intermetallics had no influence on thermal fatigue properties. Cu/sub 6/Sn/sub 5/ eta-phase whiskers formed at the intermetallic solder interface. Thermal cycling tests were performed on both joints using a -55/sup 0/C to 125/sup 0/C cycle and 19% imposed shear strain. Failures in 5Sn-95Pb occurred at Pb grain boundaries. Isothermal fatigue tests on 5Sn-95Pb give similar results. A heterogeneously coarsened region of both Pb and Sn-rich phases develops within the 60Sn-40Pb solder joints. Cracks initiate and propagate through the heterogeneously coarsened region. Heterogeneous coarsening and failure occurs in high and low thermal cycles. Isothermal fatigue cannot be compared to thermal fatigue results of 60Sn-40Pb on Cu. 115 refs., 105 figs., 5 tabs.

• Research Organization: Lawrence Berkeley Lab., CA (USA)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 6114447
• Report Number(s): LBL-23879; ON: DE88001392
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360102* -- Metals & Alloys-- Structure & Phase Studies
360103 -- Metals & Alloys-- Mechanical Properties
ALLOYS
COOLING
COPPER
CRACKS
CRYSTAL STRUCTURE
CRYSTALS
DIAGRAMS
ELECTRON MICROSCOPY
ELEMENTS
FABRICATION
FATIGUE
GRAIN BOUNDARIES
JOINING
JOINTS
LEAD ALLOYS
MECHANICAL PROPERTIES
METALS
MICROELECTRONICS
MICROSCOPY
MICROSTRUCTURE
MONOCRYSTALS
PHASE DIAGRAMS
POLISHING
SEGREGATION
SOLDERED JOINTS
SOLDERING
STRAINS
SURFACE FINISHING
TEMPERATURE EFFECTS
THERMAL CYCLING
THERMAL FATIGUE
TIN ALLOYS
TRANSITION ELEMENTS
TRANSMISSION ELECTRON MICROSCOPY
WELDING
WHISKERS