No abstract

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 Joint Electron Device Engineering Council (JEDEC) bend test standard for handheld components.Index Terms-Cell phone, cyclic bending, field conditions, finiteelement modeling, four-point bend, handheld, key presses, life prediction, personal digital assistant (PDA), reliability testing, solder joint fatigue, three-point bend.

A characterization study is undertaken to monitor damage progression at the second-level interconnect in BGA’s on flip-chip electronic packages. Specifically, the progression of solder joint cracking under use conditions (thermal and combined thermomechanical loading) is investigated. The study uses a multi-color dye and peel failure analysis technique to track the initiation and propagation of solder joint cracks under loading. The approach being used differs from conventional failure analysis techniques in that multiple measurements of damage growth are obtained from the same part providing a full damage history. By using multiple dye colors, all crack initiation points, directions of propagation, and surface crack areas are obtainable experimentally. The scope of the study includes investigating the impact of such factors as die size, package size, BGA size, BGA pitch, enabling load, and internal heat spreaders (IHS’s) on the damage history observed. Based on this study, investigation of sequential loading can be pursued to identify directions and design guidelines for improving solder joint reliability of future BGA’s on flip-chip electronic packages.

For handheld electronic applications such as cell phones and Personal Digital Assistants (PDAs), drop/impact could result in considerable flexure of the printed circuit board (PCB) mounted inside the cell phone housing. The mechanical stresses may cause electrical failure of the components, with typical failure mechanisms of board trace cracking, solder joint fatigue, and solder pad cracking. A standardized test needs to be developed to assess reliability of handheld components subjected to impacts. The test should facilitate high volume testing, maximize margin for safety factors, and capture the failure mechanisms in the field environment. To develop the reliability test using use conditions based reliability methodology, comprehensive characterization of the mechanical field stresses during end use conditions is particularly essential. This paper discusses complete cell phone drop characterization along with the shock test developed to test the components subjected to such drops. Novel fixtures have been designed to simulate free fall of the cell phone in specific orientations. After the complete characterization of cell phone use conditions, board level shock test has been selected to assess component reliability. Test repeatability, number of components on the test board, and layout of the components are some of the factors considered during the board level shock test development. Several parameters like screw and washer designs, torque have been studied to yield excellent test repeatability. Nonlinear Dynamic Finite Element Simulation has been performed to provide more insight into the interaction of the bending modes and its impact on the solder joint failures. This paper demonstrates the process of understanding use conditions, developing reliability tests, validating test results and driving industry standards.