A Novel Method for Alignment Deviation Automatic Correction in Wafer-level Flip-chip Direct Packaging

摘要

In the alignment process of flip-chip packaging, it is a key challenge to accurately align the solder ball array (BGA) and substrate. Due to the increase in the number of chip pins and the density of solder balls, advanced flip-chip packaging technology sets new requirements for fast and accurate alignment and automatic correction compensation. That is, in addition to the high-precision positioning of the XY axis, high-precision θ-axis adjustments are required for real-time alignment deviations. In the traditional motion stages, linear motor and DDR motor series are adopted for cooperative precision positioning, causing the problem of multi-axis coupling errors, lower positioning efficiency, and complicated controlling process. Therefore, in order to automatically adjust the alignment error, combining with the traditional positioning stage in a macro-micro composite manner, a 3-RRR parallel flexure microcompensator (PFM) is designed in this paper. Aiming at the problem that the displacement sensor cannot effectively detect the coupling motion displacement of the PFM in XYθ-axes, the sub-pixel visual inspection method (SVI) is proposed to solve this problem. Finally, in order to evaluate the effectiveness of the method, with the SVI-based closed-loop PID control strategy, a series of tests are successfully implemented, the results prove that the X-axis tracking error rate is reduced to 1.5%, the Y-axis tracking error rate is reduced to 3.4%, and the θ-axis tracking error rate is kept within 0.5%.