Abstract
In this work, a method that minimizes printed wiring board (PWB) warpage by dummy pattern design is proposed. This work suggests that dummy patterns are placed on a preset discretized location in the PWB to reduce the warpage. On each discretized candidate area, the dummy pattern can be set or unset. The warpage is numerically simulated based on direct modeling of the as-is PWB patterns to evaluate the warpage alongside the dummy pattern design set. The optimal pattern that minimizes warpage is determined using the human-based genetic algorithm where the objective function is evaluated by the structural simulation. The optimization method is realized in a spreadsheet that allows scripting language with which the input and output files of the simulation tool can be modified and read. Two different cases have been tested and the results show that the method can determine the optimal dummy patterns. The measured and simulated deflections agree well with each other. Moreover, it has been shown that certain dummy pattern designs that should reduce the warpage can be sought by the optimization.
Highlights
Warpage of the printed wiring board (PWB) raises serious quality issues including assemblage and long-term reliability [1,2,3,4]
This study proposes a method that can systematically set the dummy pattern in the PWB
The deflection has been evaluated by structural simulation
Summary
Warpage of the printed wiring board (PWB) raises serious quality issues including assemblage and long-term reliability [1,2,3,4] It incurs component misalignments and interconnect failures which can result in the failure of the entire assembly [2,5]. When heating up for the reflow process followed by cooling down to room temperature, the package experiences a dramatic difference in thermal strains depending on the location and materials during the cooling down. If such strains are restrained by mechanical joining, the corresponding residual stress will remain
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