The deformation properties of near-eutectic Sn-Ag-Cu alloy were measured in temperatures ranging from Ϫ25 to 125°C, and down to strain rates of about 10 ϫ 10 Ϫ9 . Results have been combined into a stress versus strain rate master curve. The measurements were done with dog-bone specimens that have a 1-mm diameter, which corresponds to a typical solder joint diameter in ball grid arrays (BGAs). Effects of cooling rate were also studied, with cooling rates from 0.1 to 1 degrees/sec. The stress exponent of the fast-cooled samples was high, about 16. The activation energy was about 1 eV. The relatively high temperature dependence suggests that bulk diffusion is dominating. Optical microscopy, scanning electron microscopy (SEM) and electron backscattering diffraction (EBSD) were used to study the microstructures of the test samples. The slower cooled samples had large Ag3Sn plates, but the size of the plates was significantly reduced with the faster cooling rates. The yield strength increased with cooling rate, reflecting the larger amount of alloying elements remaining in the solution and smaller, dispersed precipitates. For comparison, experiments were also performed on binary AgSn and CuSn solders, pure Sn, and with two reduced silver content SAC alloys, Sn-2.5% Ag-0.7% Cu and Sn-3.0% Ag-0.7% Cu.

Purpose The purpose of this paper is to describe a novel methodology for predicting reliability for consumer electronics or any other hardware systems that experience a complex lifecycle environmental profile. Design/methodology/approach This Physics-of-Failure–based three-step methodology can be used to predict the degradation rate of a population using a Monte Carlo approach. The three steps include: using an empirical equation describing the degradation of a performance metric, a degradation consistency condition and a technique to account for cumulative degradation across multiple life-cycle stress conditions (e.g. temperature, voltage, mechanical load, etc.). Findings Two case studies are provided to illustrate the methodology including one related to repeated touch-load induced artifacts for displays. Originality/value This novel methodology can be applied to a wide range of applications from mechanical systems to electrical circuits. The results can be fed into the several stages of engineering validation to speed up product qualification.

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Display light guides, commonly constructed of a polymer such as polymethyl methacrylate (PMMA), are known to be susceptible to moisture absorption, swelling, and warping in the field when exposed to elevated ambient humidity levels. This work presents a quantitative theoretical framework for calculating water absorption over time. In addition, a simple theory is laid out, which connects mass absorption of water to linear expansion of the polymer. Finally, a simple quantitative analysis of out-of-plane warping of the light guide is presented. Experimental data from laboratory PMMA coupons and two different sizes of large displays are used to establish the values of key parameters of the theoretical model. General purpose results for any size of PMMA display are presented. The approach can easily be adapted to light guides fabricated using other polymers.