Modified Norris–Landzberg Model and Optimum Design of Temperature Cycling ALT

Accelerated life testing (ALT) is an effective way to assess the lifetime of a product. Due to the complex nature of its testing profile, it is difficult to carry out temperature cycling ALT. This paper establishes a modified Norris–Landzberg model as acceleration model, and proposes the optimum design method of temperature cycling ALT. First, the FEA method is used to study the influence of temperature cycling profile parameters on the thermal fatigue life of 63Sn–37Pb solder joints. Then, a modified Norris–Landzberg model is proposed by introducing ramp time and dwell time with an added weight value. Finally, the temperature cycling ALT is regarded as a special multi-stress ALT to study its optimum design method. The uniform design theory is used to determine the combined mode. The optimum model is established with the objective of minimizing the asymptotic variance of the estimation of median lifetime under normal use conditions, and the simulation example shows the workability of the proposed method

Body-centered-cubic Ni and its magnetic properties

The body-centered-cubic (bec) phase of Ni, which does not exist in nature, has been achieved as a thin film on GaAs(001) at 170 K via molecular beam epitaxy. The bec Ni is ferromagnetic with a Curie temperature of 456 K and possesses a magnetic moment of 0.52 \uc2\ub1 0.08 \uce\ubcB/atom. The cubic magneto-crystalline anisotropy of bec Ni is determined to be +4.0 \uc3\u97 105 ergs \uc2\ub7 cm-3, as opposed to -5.7 \uc3\u97 10 4 ergs \uc2\ub7 cm-3 for the naturally occurring face-centered-cubic (fcc) Ni. This sharp contrast in the magnetic anisotropy is attributed to the different electronic band structures between bec Ni and fcc Ni, which are determined using angle-resolved photoemission with synchrotron radiation