Placement of surface mount components: machine accuracy and performance modeling

An experimental study was undertaken to determine the accuracy and performance characteristics of a surface mount placement system. Calibrated glass components and glass plates were used in these experiments to decouple the influence of the board and device related distortions. The metric used for the performance-measure included the translational and rotational misalignment of devices subsequent to placement. The results clearly demonstrate that the fiducial parameters are more crucial than many other process variables. The measurements indicate that the machine accuracy is ±1.25 mils. Although it may seem excellent, this figure of merit, as determined using calibrated rigid-bodies for devices and substrates, accounts for 16.7% of the budgeted margin of error for misalignment in 25 mil pitch assembly (using a quality metric of half of the pad displacement for misalignment). Its error contribution increases exponentially as the leadpitch decreases below 25 mils. At 10 mil pitch, it amounts to more than 50% of the margin of errors