Creep And Isothermal Fatigue Behaviour Of Eutectic SnPb, SnBi And SnZn Solders For Microelectronic Packaging At Mildly Elevated Temperatures
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Date
2011-01
Authors
Hashim, Md Amin
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Publisher
Universiti Sains Malaysia
Abstract
Interconnect materials are used to connect surface mounting components and other passive and discrete circuit components on to copper pads or lands, and in holes on the printed circuit boards. Presently, the industrial practice is using thermal cycling as a method for reliability testing of circuit boards with assembled components. Bulk specimens of 63Sn37Pn solder alloy were subjected to isothermal fatigue at three mildly elevated temperatures (30, 40 and 50oC), loading frequencies (6, 60 and 600 CPM) and at different applied peak stresses (ranging from 8.75 to 33.25 MPa). The specimens were found to fail predominantly due to creep with activation energy of about 60 KJ mol-1 with stress exponents varying between 1 and 2, and under the same experimental conditions, static creep tests showed activation energy of 85 KJ mol-1 and an average stress exponents of 1.5. Strain-controlled fatigue tests conducted at different temperatures, loading frequencies, three different applied peak strains and different R-values resulted in the mean stress responses to decay exponentially. At R=-1, the mean stress responses decayed instantaneously to zero value for all applied peak strains, loading frequencies and temperatures. Isothermal fatigue tests conducted at R=-1, 600 CPM frequency and at two different temperatures showed creep damage repair mechanism and enhances creep-fatigue interaction phenomenon in the bulk solder material during mechanical cycling. Fractography of fractured specimen showed a change in fracture mechanism, that is, from micro-voids to micro-cracks observations. Even though, thermal cycling data were unavailable for comparison with those from isothermal fatigue, observations obtained from the experiments conducted suggested suitable and appropriate methods in conducting isothermal fatigue tests. Hence, in comparison with presence of some thermal cycling data, the isothermal fatigue test is a proposed alternative test for reliability testing of eutectic interconnects.
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Keywords
The isothermal fatigue test is a proposed , alternative test for reliability testing of eutectic interconnects