The Dissimilar Self-Alignment Characteristics of Smaller Passive Components in the Length and Width Directions

Motivation: As passive components' size gets smaller, quality rejects due to overhangs after the reflow appear more frequently. This situation is partly because the pass-fail criterion is set based on the offset concerning the component and pad dimensions. Therefore, understanding the self-alignment characteristics of electronic components becomes very critical for surface-mount assembly yield. This research investigates the dissimilarity of selfalignment in the length and width directions. Approach: To avoid the argument of sample to sample variations, data are collected from 81 printed circuit boards (PCB) and 182,250 assembled components. Within a PCB, 25 different solder paste printing offset locations and 81 component placement offset settings are implemented. Component-placement positions before and after the reflow are monitored. The results are compared to identify different component sizes' self-alignment characteristics in the length and width directions. Key findings: The misalignment of smaller passive components, e.g., R0402M (0.40 mm × 0.20 mm), is worse than the larger component under the identical solder paste printing and component placement conditions. Furthermore, the self-alignment characteristic in the length direction of these passive components, e.g., R0402M, to R1005M (1.00 mm × 0.50 mm) is superior to that of width direction. The observations are not consistent with the results found in earlier research that reported on the capacitors and resistors in variant sizes, e.g., 0402M (0.40 mm × 0.20 mm), to 3216M (3.20 mm × 1.60 mm).