| The electronics packaging domain has evolved significantly over the last few decades. Miniaturization, high functionality, low cost and excellent reliability have been the hallmarks of this evolution. An outcome of the demands is 'stacked die DRAMs'. These innovative packages are entering high-volume manufacturing. At the module level, the use of polyimide flexible substrates for the assembly of compactly folded memory modules has proven to be useful for applications in high-end server boards. The use of rigid substrates (memory cards) to assemble stacked high density memory modules is a unique technology that was studied in this research endeavor.;This product technology, named bridge LRDIMM, uses two independently built high density memory cards that can be stacked together using an interposer and a heat sink assembly. LRDIMM-related product technology is relatively new, and has not been systematically and thoroughly researched. There is a definite need for methodical research with respect to product design and process stability, which is the overall objective of this research endeavor. The experimental approach utilized for this study enabled the characterization of the bridge LRDIMM sub-assembly reflow process, and provided an understanding of the effects of interposer weight on the solder joint stand off and substrate warpage during reflow. A threshold weight was calculated based on this study. The evaluation of the stacking mechanism enabled the analysis and improvement of the existing stacking mechanism. Therefore, a stable repeatable stacking process was established based on the outcome of this experimental analysis. Next, to enhance the thermal performance of the module during operation, cooling guidelines were established based on the results of a simulation and an experimental study. A convective fan with a minimum air speed of 4 m/s was recommended. Further, the assembly process was validated by performing reliability tests on the newly assembled modules. The results indicated that the module had the required robustness in design and quality to perform reliably in the field. |
