Use-condition-based cyclic bend test development for handheld components

For handheld electronic applications such as cell phones and personal digital assistants (PDAs), repeated key strokes could result in considerable flexure of the printed circuit board (PCB) mounted inside the housing. In this study, a standardized four-point bend test, including test board design, test setup, and test input level, has been developed. The S-N curve has been obtained by plotting the reliability at all deflection levels as a function of solder joint strain energy density. The effect of test frequency has also been evaluated. The reliability model prediction of three-point bend reliability matches the experimental data extremely well. The transfer function between reliability stressing and field condition is a strain-energy-density-based power law relationship. Finite element simulation has been conducted for the worst-case cell phone subjected to key presses. The use condition data including strain profiles and frequency have been incorporated in the field life prediction. The four-point bend performance can be converted into the component reliability during cell-phone field use conditions. This study establishes the correlation between the use conditions and reliability tests. The cyclic four-point bend test will be implemented in the JEDEC bend test standard for handheld components.