Yield estimation through component placement accuracy evaluation in surface mount PWB assembly

The effectiveness of the placement process in ultrafine pitch surface mount PWB assembly is influenced primarily by the accuracy of the Printed Wiring Boards (PWBs), the dimensional stability of the Surface Mount Components (SMCs), and the capability of the pick and place machine used. Engineers in a PWB assembly facility often need to evaluate the capability of their respective manufacturing processes (more specifically, their SMC placement process). Consequently, they need to understand the variations associated with the primary attributes of the PWBs, the SMCs and the placement equipment, and their impact on the yields of the placement process. This knowledge will guide the manufacturer in determining alternative courses of action which might improve process yields. This research attempted to understand how variations in the functional parameters of the PWBs, peripheral leaded SMCs and pick and place machines affect the objective function that was considered, namely the lead to pad coverage. A global system model was formulated to quantitatively determine the impact of each set of inputs on this objective function. Computer-based simulation was used to estimate the lead to pad coverage. This solution methodology provided a reasonable estimate of the distribution of the lead to pad coverage based on the specific PWB, SMCs and placement machine characteristic data. The software developed to simulate the placement process is user friendly. The output format used combines textual and graphical modes. The simulation software has been rigorously tested and verified, and found to provide excellent results.