Influence of the Substrate on the Creep of SN Solder Joints

Abstract

The creep rate of Sn solder joints is noticeably affected by joint metallization. Cu|Sn|Cu joints have significantly higher creep rates than Ni|Sn|Cu joints, which, in turn, have higher creep rates than Ni|Sn|Ni joints. Replacing Ni by Cu on both substrates increases the creep rate at 333 K (60°C) by roughly an order of magnitude. The increased creep rate appears with no apparent change in the dominant creep mechanism; the change in the constitutive equation for creep (the Dorn equation) is in the pre-exponential factor. The decreased creep rate on substituting Ni is accompanied by an increase in the hardness of the polygranular solder but a decrease in the nanohardness of the grain interiors. The source of the strong influence of the Ni substrate appears to be the introduction of an array of Ni 3 Sn 4 intermetallic precipitates along the grain boundaries. These precipitates inhibit grain boundary sliding, boundary reconfiguration, and grain growth during creep. The intermediate creep rate of the asymmetric Ni|Sn|Cu joint has two causes: a decrease in grain boundary mobility due to precipitate decoration and a restriction in the free volume of the joint due to rapid intermetallic growth from the substrate on the Ni side. The sources of this anomalous intermetallic growth are discussed.

Segregation engineering enables nanoscale martensite to austenite phase transformation at grain boundaries: A pathway to ductile martensite

“…A kinetic analysis of the segregation rate of Mn at 450°C was consistent with bulk diffusion of these elements in ferrite and resulting segregation. Further similar results on Mn segregation to grain boundaries has been reported in other studies [59][60][61][62][63][64][65][66][67]. Differences among the various results are due to the different alloys and the corresponding chemical potentials for Mn and also due to site competition effects.…”

The effects of creep on electromigration behaviors in Sn-based Pb-free solder joints

“…Failure mechanisms in microsystem products are many, and failures can be caused by either thermal, electrical, and mechanical or a combination of them [4] . The most reliability concerns on solder joint are generally the generation of microstructural damage by the action of high current densities [5][6][7] , the rate of creep deformation as a function of temperature and load and development of interfacial intermetallic during aging [3,8,9] . It is clearly that the majority of current investigations are focusing on the failure mechanisms under single factor such as electromigration (EM), thermomechanical fatigue (TMF) and creep, respectively.…”