Improving fatigue life in near-eutectic Sn Pb solders
Due to technical advances in packaging technology, solder joint thermal shear fatigue failures pose reliability concerns and limit current packaging designs in the electronics industry. Past work has shown that thermal fatigue failures, as well as isothermal fatigue and creep failures, in the commonly used near-eutectic Sn-Pb solders are preceded by the formation of a band of coarsened material. Examination of crept and fatigued eutectic solder joints shows that shear deformation concentrates along relatively soft heterogeneities, the eutectic grain and colony boundaries, in the as-cast microstructure which happen to line up into long straight bands parallel to the applied shear strain. Improvement of the fatigue properties requires an elimination or, at least, a reduction in the length of these long straight boundaries. Several methods of doing that are proposed. These methods basically fall into two groups: one involving homogenization of the as-cast microstructure aimed at eliminating these heterogeneities and the other involved with breaking up the as-cast microstructure in such a way that long straight boundaries do not form parallel to the direction of shear. To study the effect of homogenization of the microstructure, room temperature aging of solder joints was studied. Softening was found to occur over a period of about 40--50 weeks levelling off at about 70--75% of the initial strength (31 MPa). The effect of breaking up the as-cast microstructure was studied by comparing various off-eutectic alloys. The alloys studied consisted of Pb with 40 and 50 wt. % Sn in addition to the near-eutectic 63Sn-37Pb alloy. In addition, the Pb-rich 20Sn-80Pb and 5Sn-95Pb alloys were studied in fatigue at 75{degrees}C. 170 refs., 62 figs.
- Research Organization:
- Lawrence Berkeley Lab., CA (USA)
- Sponsoring Organization:
- USDOE; USDOE, Washington, DC (USA)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 5555245
- Report Number(s):
- LBL-30605; ON: DE91013844
- Resource Relation:
- Other Information: Thesis (Ph.D)
- Country of Publication:
- United States
- Language:
- English
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