Search

The critical strain energy release rate for the solder joint fracturewasmeasured as a function of the strain rate and the mode ratio of loading. These data are useful in predicting the fracture of solder joints loaded under arbitrary combinations of tension and shear during the impact conditions typical of falling portable electronic devices. In this study, strain rates from quasi-static (close to 0 s-1) to 61 s-1 were investigated at phase angles from 0 to 60°, typical of the range found in microelectronic devices. Copper-solder-copper double cantilever beam (DCB) model specimens were prepared using SAC305 solder at cooling rates and times above liquidus typical of actual ball grid arrays (BGAs). A drop tester was designed and built to achieve different strain rates at various mode ratios. The critical initiation strain energy release rate, Jci, increased about 70% fromquasi-static to intermediate strain rates, before decreasing by more than 67% from intermediate strain rates to 42 s-1. [ABSTRACT FROM AUTHOR]

Solder joint fracture toughness was measured using double-cantilever-beam specimens over a range of strain rates and mode ratios as a function of five key processing parameters: the type of lead-free solder alloy, solder thickness, time above liquidus, aging time, and the geometry of the end of the solder layer. Although the toughness was a strong function of the loading phase angle and strain rate, relatively small differences were due to the solder composition, time above liquidus, and aging. The effects of solder thickness and local end geometry were found to be significant only at the higher strain rates. [ABSTRACT FROM AUTHOR]

Solder joint fracture toughness was measured using double-cantilever-beam specimens over a range of strain rates and mode ratios as a function of five key processing parameters: the type of lead-free solder alloy, solder thickness, time above liquidus, aging time, and the geometry of the end of the solder layer. Although the toughness was a strong function of the loading phase angle and strain rate, relatively small differences were due to the solder composition, time above liquidus, and aging. The effects of solder thickness and local end geometry were found to be significant only at the higher strain rates. [ABSTRACT FROM AUTHOR]

Abstract: Copper bars were soldered along their length with a thin layer of lead-free Sn3.0Ag05.Cu alloy under standard surface mount processing conditions to prepare double cantilever beam (DCB) specimens. The geometry of the DCBs was varied by changing the thickness of the solder layer and the copper bars. These specimens were then fractured under mode-I and two mixed-mode loading conditions. The initiation strain energy release rate, Gci , increased with the relative fraction of mode-II, but was unaffected by the changes in either the substrate stiffness or the solder layer thickness. However, the steady-state strain energy release rate, realized after several millimeters of crack growth, was found to increase with the solder layer thickness at the various mode ratios. The crack path was found to be influenced by mode ratio of loading and followed a path that maximizes the von Mises strain rather than maximum principal stress. Finally, some preliminary results indicated that the loading rate significantly affects the Gci . [Copyright &y& Elsevier]

Abstract: Double cantilever beam (DCB) specimens were prepared with three different time–temperature profiles to achieve distinct intermetallic microstructures and then tested under mode I and various mixed-mode loading conditions to obtain the R-curves. The time above solder liquidus and the cooling rate were selected to be representative of typical microelectronics production. Both the initiation strain energy release rate and the steady-state values were found to increase with the relative amount of mode II loading and decrease with the thickness of the intermetallic compound layer between the solder and the copper. The effect of the local geometry of the end of the solder layer was found to have only a small effect on the initiation strain energy release rate. [Copyright &y& Elsevier]

Ball grid array (BGA) test vehicles, assembled in a standard surface mount technology (SMT) line, were used to prepare fracture specimens in seven configurations in order to measure solder ball fracture loads at two different strain rate regimes for a range of loading mode ratios. The measured strengths of the specimens were compared with the predictions of a cohesive zone model (CZM). The phase angle of the specimens under bending was found to be close to mode I and hence the fracture criterion was governed predominantly by mode I parameters. The mode I peak stress and fracture energy of the CZM were obtained in two separate ways: (i) The fracture energy was obtained from separate copper-solder-copper double cantilever beam (DCB) tests, while the peak stress was obtained from one of the BGA specimen configurations. (ii) One BGA specimen configuration was used to obtain the mode I fracture energy, and the peak stress was assumed to be given by the yield stress. In both cases (i) and (ii), the rising slopes of the modes I and II traction-separation laws corresponded to the compliance of the system. The accuracy and generality of these CZ models was then assessed by using them to predict the fracture loads of the remaining BGA specimens that had different geometries and hence fracture strengths. The fracture loads predicted using either model were in reasonable agreement with the measured forces at a given strain rate. Therefore, once the CZM parameters have been defined for a given solder system using one BGA specimen, the CZM could predict the fracture of BGA solder joints with different geometries and strengths. [ABSTRACT FROM AUTHOR]

The mixed-mode fracture energies of copper–SAC305–copper solder joints were measured using both an Arcan-type specimen and a double-cantilever beam (DCB) specimen. The critical strain energy release rate, J ci , values obtained from Arcan-type specimens were in the range of 10–80 J/m 2 , depending on the strain rate and phase angle of loading, while those obtained from DCB specimens were much higher, in the range of 380–2300 J/m 2 . This large difference in the measured J ci values, which is consistent with the literature, was explained in terms of the stress distributions, constraint and plastic zone sizes in the solder layers in these two specimens. [ABSTRACT FROM AUTHOR]

Fracture experiments with ball grid array (BGA) specimens having different adherend rigidities were performed under bending loads at intermediate strain rates (0.2–1 s −1 ) and a high strain rate of 30 s −1 . A cohesive zone model (CZM) was established and the predictive capability of the model was assessed for the specimens with different rigidities. The predicted fracture loads were within 12% of the measured forces when the CZM parameters were obtained using specimens with a similar degree of constraint. This suggests that in many practical cases, the effect of adherend stiffness can be neglected in predicting the strength of BGA solder joints. [ABSTRACT FROM AUTHOR]