An Improved Automated SPI Data Analysis Report Generator for Printed Circuit Board Assembly

The growing need for dependable assembly procedures in electronic manufacturing, driven by the trend toward miniaturization, necessitates effective measures to counteract reflow defects arising from chip warpage in Ball Grid Array (BGA) packages. Out-of-plane deformation is common in BGAs, attributed to varying thermal expansion coefficients, and eventually results in opens, Head-in-Pillow (HIP), or bridging defects. This work addresses the shortcomings of existing stencil design guidelines, which often overlook chip warpage, leading to common reflow defects. We propose a novel approach utilizing the Shadow Moiré technique to numerically quantify chip warpage at all pin locations, enabling the automatic optimization of stencil apertures. By processing this data with an advanced algorithm, we design apertures considering the following parameters: localized chip warpage, stencil thickness, Cu pad size, and pitch. This automated method reduces the reliance on engineer experience and eliminates the need for extensive experimentation. In this research, we have substantiated a previously suggested framework by applying emulated warpage data and evaluating its effectiveness using three commercial BGA packages susceptible to warping during reflow. Through empirical experiments and utilizing the proposed framework, we successfully designed the optimal aperture opening for each Cu pad under the chip, automatically, eliminating defects like opens, bridging, and HIP during reflow. The robustness and reliability of this approach have been verified for addressing challenges associated with chip warpage in the Surface Mount Technology (SMT) reflow process. The outcomes underscore significant improvements in defect prevention and overall assembly quality.