Creep of thermally aged SnAgCu-solder joints
ABSTRACT The creep behaviour of Sn96.5Ag3.5- and Sn95.5Ag3.8Cu0.7-solder was studied specifically for its dependence on technological and environmental factors. The technological factors considered were typical cooling rates and pad metallizations for solder joints in electronic packaging. The environmental factors included microstructural changes as a result of thermal aging of solder joints. Creep experiments were conducted on three types of specimens—flip–chip joints, PCB solder joints and bulk specimens. flip–chip specimens were altered through the selection of various under bump metallizations (Cu vs. NiAu), cooling rates (40 K/min vs. 120 K/min), and thermal storage (24 h, 168 h, and 1176 h at 125 °C). PCB solder joints were studied by using a copper pin soldered into a thru-hole connection on a printed circuit board having a NiAu metallization. Bulk specimens contained the pure alloys. The creep behaviour of the SnAg and SnAgCu solders varied in dependence of specimen type, pad metallization and aging condition. Constitutive models for SnAg and SnAgCu solders as they depend on the reviewed factors are provided.
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ABSTRACT: Extensive data on 62Sn36Pb2Ag, 60Sn40Pb, 96.5Sn3.5Ag, 97.5Pb2.5Sn, and 95Pb5Sn solder are presented. All of the data were collected on soldered assemblies to properly account for the effects of grain size and intermetallic compound distribution. Tensile and shear loading were employed in the strain rate range between 10<sup>-8</sup> and 10<sup>-1 </sup> s<sup>-1</sup> and the temperature range between 25 and 135°C. It is remarkable to note that all of the data can be fit to the same general form of constitutive relations; i.e., only the constants depend on the solder alloy. The derived constitutive relations are used to predict solder joint response under thermal cycling. Based on the calculated hysteresis loops, it is apparent that each solder will have a different acceleration factor between field use cycling and accelerated test cyclingIEEE Transactions on Components Hybrids and Manufacturing Technology 01/1993;
- Journal of Electronic Packaging - J ELECTRON PACKAGING. 01/1995; 117(2).
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ABSTRACT: A multiphase diffusion model was constructed and used to analyze the growth of the ε- and η-phase intermetallic layers at a plane Cu-Sn interface in a semi-infinite diffusion couple. Experimental measurements of intermetallic layer growth were used to compute the interdiffusivities in theε andη phases and the positions of the interfaces as a function of time. The results suggest that interdiffusion in the ε phase(≈D ε) is well fit by an Arrhenius expression with D0 = 5.48 × 10−9 m2/s andQ = 61.9 kJ/mole, while that in the η phase (≈Dη) has D0 = 1.84 × 10−9 m2/s andQ = 53.9 kJ/mole. These values are in reasonable numerical agreement with previous results. The higher interdiffusivity in theη phase has the consequence that theη phase predominates in the intermetallic bilayer. However, the lower activation energy for interdiffusion in theη phase has the result that theε phase fills an increasing fraction of the intermetallic layer at higher temperature: at 20 °C, the predicted ε-phase thickness is ≈10 pct of that ofη, while at 200 °C, its thickness is 66 pct of that ofη. In the absence of a strong Kirkendall effect, the original Cu-Sn interface is located within theη-phase layer after diffusion. It lies near the midpoint of theη-phase layer at higher temperature (220 °C) and, hence, appears to shift toward the Sn side of the couple. The results are compared to experimental observations on intermetallic growth at solder-Cu interfaces.Metallurgical and Materials Transactions A 02/1992; 23(3):857-864. · 1.73 Impact Factor