The compression stress-strain behavior of Sn-Ag-Cu solder

The shear strength behavior and microstructural effects after aging for 100 h and 1,000 h at 150°C are reported for near-eutectic Sn-Ag-Cu (SAC) solder joints (joining to Cu) made from Sn-3.5Ag (wt.%) and a set of SAC alloys (including Co-and Fe-modified SAC alloys). All joints in the as-soldered and 100-h aged condition experienced shear failure in a ductile manner by either uniform shear of the solder matrix (in the strongest solders) or by a more localized shear of the solder matrix adjacent to the Cu 6 Sn 5 interfacial layer, consistent with other observations. After 1,000 h of aging, a level of embrittlement of the Cu 3 Sn/Cu interface can be detected in some solder joints made with all of the SAC alloys and with Sn-3.5Ag, which can lead to partial debonding during shear testing. However, only ductile failure was observed in all solder joints made from the Co-and Fe-modified SAC alloys after aging for 1,000 h. Thus, the strategy of modifying a strong (high Cu content) SAC solder alloy with a substitutional alloy addition for Cu seems to be effective for producing a solder joint that retains both strength and ductility for extended isothermal aging at high temperatures.

Section: Discussionsupporting

confidence: 57%

Elevated temperature aging of solder joints based on Sn-Ag-Cu: Effects on joint microstructure and shear strength

Anderson

Harringa

2004

“…For example, recent studies have shown that small differences in Cu content affect yield stress. 16 Therefore, it is important to establish an accurate and thorough database of time-dependent deformation for the Sn-Ag-0.6Cu composition, particularly for the development of a high-fidelity computational model that predicts the long-term reliability of soldered interconnections.…”

Section: Introductionmentioning

confidence: 99%

“…The compression test methodology was selected, based upon its successful use for measuring the time-independent properties of the Sn-Ag-0.6Cu solder. 2,16 The effect of the starting microstructure was examined through three test series. The first test series, the results of which are described in this report, used samples in the as-cast condition.…”

Section: Introductionmentioning

confidence: 99%

Creep behavior of the ternary 95.5Sn-3.9Ag-0.6Cu solder—Part I: As-cast condition

Vianco

Rejent

Kilgo

2004

Self Cite

The compression creep behavior was studied for the ternary solder alloy 95.5Sn-3.9Ag-0.6Cu in the as-cast condition. Samples were tested under stresses of 2-45 MPa and temperatures of Ϫ25-160°C. There was a significant variability in the creep curve shape, strain magnitude, and steady-state strainrate properties. A multivariable linear-regression analysis of the steady-state strain-rate data, using the sinh-law stress representation, indicated two mechanisms distinguished by low-and high-temperature regimes of Ϫ25-75°C and 75-160°C, respectively. The sinh-law stress exponent (n) and apparentactivation energy (∆H) in the Ϫ25-75°C regime were 4.4 Ϯ 0.7 kJ/mol and 25 Ϯ 7 kJ/mol (63% confidence intervals), respectively. Those same parameters in the 75-160°C regime were 5.2 Ϯ 0.8 kJ/mol and 95 Ϯ 14 kJ/mol, respectively, for the high-temperature regime. The values of ∆H suggested a short-circuit diffusion mechanism at low temperatures and a lattice or bulk-diffusion mechanism at high temperatures. The stress dependency of the steady-state strain rate did not indicate a strong power-law breakdown behavior or a threshold stress phenomenon. Cracks and grain-boundary sliding were not observed in any of the samples. As the creep temperature increased, a coarsened particle boundary and particle depletion zone formed in the region of fine Ag 3 Sn particles that existed between the Sn-rich phase areas. The coarsened particle boundary, as well as accelerated coarsening of Ag 3 Sn particles, were direct consequences of the creep deformation process.

“…Because recent studies have shown that small differences in Cu content can affect the mechanical properties of Sn-Ag-Cu solders, it is important to determine the creep properties database specific to the Sn-Ag-0.6Cu composition in order to maximize the fidelity of the computational model predictions. 17 A study was undertaken to assess the creep properties of bulk Sn-Ag-0.6Cu solder. In the first part of the study, the creep behavior of the Sn-Ag-0.6Cu alloy was determined for specimens in the as-cast condition.…”

Section: Introductionmentioning

confidence: 99%

Creep behavior of the ternary 95.5Sn-3.9Ag-0.6Cu solder: Part II—Aged condition

Vianco

Rejent

Kilgo

2004

Self Cite

Compression creep tests were performed on the 95.5Sn-3.9Ag-0.6Cu (wt.%) solder. The specimens were aged prior to testing at 125°C, 24 h or 150°C, 24 h. Applied stresses were 2-40 MPa. Test temperatures were Ϫ25°C to 160°C. The 125°C, 24-h aging treatment caused the formation of coarsened Ag 3 Sn particle boundaries within the larger ternary-eutectic regions. The 150°C, 24-h aging treatment resulted in contiguous Ag 3 Sn boundaries in the ternary-eutectic regions as well as a general coarsening of Ag 3 Sn particles. The 125°C, 24-h aging treatment had only a small effect on the strain-time curves vis-à-vis the as-cast condition. Negative creep was observed at 75°C for time periods Ͼ10 5 sec and stresses of 3-10 MPa. The creep kinetics exhibited a sinh term (stress) exponent, p, of 5.3 Ϯ 0.6 and an apparent-activation energy, ∆H, of 49 Ϯ 5 kJ/mol when data from all test temperatures were included. A good data correlation was observed over the [Ϫ25-125°C] temperature regime. Steady-state creep kinetics exhibited a greater variability in the [125-160°C] regime because of the simultaneous coarsening of Ag 3 Sn particles. The aging treatment of 150°C for 24 h resulted in a more consistent stress dependence and better reproducibility of the creep curves. Negative creep was observed in samples aged at 150°C for 24 h when tested at Ϫ25°C, 25°C, and 75°C. The values of p and ∆H were 4.9 Ϯ 0.3 kJ/mol and 6 Ϯ 5 kJ/mol, respectively. Only a slight improvement in the data correlation was observed when the analysis examined separated [Ϫ25-75°C] and [75-166°C] temperature regimes. Creep testing did not cause observable deformation in any of the sample microstructures.