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

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 theta-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 XY theta-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 theta-axis tracking error rate is kept within 0.5%.