A novel placement method for mini-scale passive components in surface mount technology

Abstract

This paper aims to propose a novel placing method, i.e., place-between-paste-andpad (PB), for mini-scale passive components to enhance electronic assembly lines' yield. PB means a component is designed to be placed at the midpoint between the pastes and pads on the length direction while it aligns with the pads' center on the width direction. An experiment that involves 12 printed circuit boards (PCB) is designed and conducted to get comparative results. Four PCBs are employed for place-on-pad (PP), place-on-paste (PPS), and PB separately. On each board, 375 resistors R0402M (0.40 mm × 0.20 mm) are assembled horizontally.To study the components' misalignment under various solder paste offset conditions in different placement methods, a stencil with 25 solder paste offset settings is utilized. Based on this experiment's results, PB has superior performance to the other two methods to minimize components' misalignment. Regarding the number of acceptable components when post-reflow offsets are within 25% of components' dimensions, PB and PP have equivalent performances, and they both outperform PPS. Furthermore, PB is a lowcost placing strategy because PB needs not the real-time communication between the solder paste inspection machine and the pickand-place machine. With the miniaturization trend in electronic products, the postreflow components' misalignment is more frequently observed than before. The placement method proposed in this study is expected to offer a low-cost exploration in the component pick-and-place procedure to enhance the surface mount technology (SMT) assembly quality.Keywords SMT assembly • mini-scale passive components • pick-and-place • place-on-pad • place-on-paste beneficial for large components in decreasing 56 the misalignment [3]-[5], it did not perform so 57 well for mini-scale components.

A Pick-and-Place Process Control Based On the Bootstrapping Method for Quality Enhancement in Surface Mount Technology

“…In [7], APC improves the assembly quality by decreasing the number of solder bridging defects. However, APC shows inconsistent and unstable results in terms of component misalignment [6]. Components placed between the solder paste and pad center tend to have smaller misalignment, but those placed farther from the solder paste location and the pad center have larger offset after soldering.…”

“…Components placed between the pad center and solder paste are located around the pad center after soldering, but those placed farther from the solder paste and the pad center show large misalignment from the pad center. PB is a rule-based strategy developed to reduce the average and variance of final misalignment by considering mounter placement accuracy [6]. PB places components at the midpoint between solder paste and pads in the length direction if the solder paste offsets are greater than 20 µm.…”

“…With the miniaturization trend in electronic products, it becomes more frequent to observe that misalignment in mini-scale components exceeds acceptable tolerances after the reflow process [6]. Advanced chip placement methods have been developed to address this issue.…”

“…PP places components directly on the pad center without considering solder paste offset. It is the traditional and prevalent method in the industry [6]. APC and PB are advanced techniques that place components away from the pad center by aligning them with the observed solder paste location.…”

“…APC improves assembly quality by reducing the occurrence of solder bridging defects in components positioned on solder paste [7]. However, since the mounter cannot place chips exactly on solder paste, APC shows a large mean and variance of component misalignment compared to PP [6]. Components placed between the pad center and solder paste are located around the pad center after soldering, but those placed farther from the solder paste and the pad center show large misalignment from the pad center.…”