Microscopic Experimental Investigation on Shear Failure of Solder Joints

Abstract

A microscopic investigation has been made on the shearing of one leaded and two leadfree solders by using an in situ SEM method. A shear lap joint specimen is designed and fabricated to accommodate a thin layer of solder alloy between copper strips. A non-contact method that measures strains in a very narrow area in the solder was applied. A laser grid was also used on the copper strip for measuring the back-face strain. Simultaneously micrographs at various stages were also taken. Where in situ measurements and micrographs are recorded they can reveal the continual development of damage and fracture mechanisms consistent with observations generated by low-cycle fatigue loading. This means that the shear test can be used as an alternative test to fatigue loading tests. By comparison, two lead-free solder specimens showed much smaller elongation to failure than the leaded solder, although all specimens showed similar sequence of events leading to final failure, including the boundary layer fracture phenomenon. The back-face strain indicator for the formation of a macro crack is due to the shifting of high stress concentration area from the joint-edge region to outside the joint region as revealed by a damage-coupled finite element procedure. The procedure also provides an estimate on the critical back-face strain.

Low-cycle fatigue failure behavior and life evaluation of lead-free solder joint under high temperature

“…It should be mentioned that the solder joint failure behavior is quite different from the solder alloy due to the presence of interfacial boundaries and size effect of the joint [10]. The thickness of a solder joint is much smaller than that of a bulk solder used for fatigue test, so that the amount of plastic deformation can be vastly different.…”

Anisotropic Crystal Plasticity Finite Element Modeling of the Effect of Crystal Orientation and Solder Joint Geometry on Deformation after Temperature Change

“…[19][20][21][22][23] Many studies examine the reliability of solder joints arising from evolution of intermetallic morphology in the interface. [24][25][26][27][28][29] In contrast to lead-tin-based solders, for which the probability of fracture is directly related to the strain amplitude, crystal orientations in initial tin-phase microstructure have a large impact on reliability of lead-free solders, [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] so damage can develop in any region of a package. To predict deformation during the TMF cycling of a solder joint, a deep knowledge of deformation mechanisms in Sn is required.…”

Quantification of creep strain in small lead-free solder joints with the in-situ micro electronic-resistance measurement

“…When there is no crack in the solder joint, its electronic-resistance Ro is computed as equation (2). h RO= pS (2) Where, p is the resistivity of Sn-3.5Ag and S is the equivalent section area of solder joint at vertical position of electric current. S = WL, W is the width and L is the length of solder joint.…”

“…SEM micrographs were captured and the load-displacement data were acquired during the shear test. Simultaneously, strains were measured with a view to compare microscopic observations of a laser grid on the copper strip and finite element analysis results [2]. Some literatures [3][4][5][6][7][8][9] have investigated and/or quantified the creep strain in small lead-free solder joints microcosmically.…”