Isothermal and thermomechanical fatigue of 63Sn/37Pb solder is studied under total strain-controlled tests. A standard definition of failure is proposed to allow inter-laboratory comparison. Based on the suggested failure criterion, load drop per cycle, the Young’s modulus and the ratio of the maximum tensile to maximum compressive stresses remain constant, and the fatigue response of the solder is stable before failure, although cyclic softening was observed from the beginning. Experimental results of isothermal fatigue tests for a total strain range from 0.3 to 3 percent show that the log-log plot of the number of cycles to failure versus the plastic strain range has a kink at the point where the elastic strain is approximately equal to the plastic strain. In this paper, it is shown how the isothermal fatigue life of near-eutectic solder at lower strain ranges can be predicted by using the experimental data of fatigue tests at high strain ranges and early stage information of a fatigue test at the strain range in question. A thermomechanical fatigue life prediction is also given based on a dislocation pile-up model. Comparison with experimental results shows a good agreement.

Amorphous carbon nitride coatings of thickness of 5 and 30 nm were deposited onto 65 and 95 mm magnetic thin-film rigid disks surfaces using single-cathode and dual-cathode magnetron sputtering systems containing nitrogen-argon plasmas. Under optimum deposition conditions, amorphous carbon nitride coatings can be synthesized on ultrasmooth thin-film disks with no significant pinholes at thickness down to 5 nm, with hardness 22–28 GPa (compared to 7–12 GPa for amorphous carbon), and r.m.s. roughness as low as 0.25 nm. These amorphous carbon nitride coatings were shown to have better contact-start-stop performance and three-to-four times better pin-on-disk contact durability compared with amorphous carbon overcoats under identical testing conditions. Amorphous carbon nitride appears to be a promising candidate overcoat material for replacing amorphous carbon in the next-generation magnetic thin-film rigid disk systems.

The effects of aging, strain range, hold time at maximum strain and temperature on the isothermal fatigue life of bulk 63Sn-37Pn solder samples over the total strain range (Δ εT) from 0.3 to 3.0 percent (tension-tension) and within the temperature range of 25° C to 100° C were studied. The cycles to failure (Nf) were defined as the number of cycles at which the ratio of the maximum tensile stress to the maximum compressive stress starts to drop appreciably. Fatigue life increases rapidly after a day or two of aging after heat treatment at 150° C for 2 hours followed by air cooling but levels off after a week. The log of fatigue life decreases linearly with increasing log of plastic strain range above Δ εT = 0.6 percent. Hold time at maximum strain dramatically decreases the cycles to failure, however, an increase of hold time more than a few minutes eventually leads to a constant Nf. Temperature variation from 25°C to 100° C was found to have little effect on the fatigue life of the solder in tests with and without hold time. Separation of Pb-rich and Sn-rich phases and cracking of the Sn-rich phases are the main modes of fracture under all conditions used. Damage is concentrated along crisscrossing shear bands oriented approximately 45 deg to the load direction.

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