In mass PCB production, fully automatic printing machines are typically utilized for the application of solder paste. When the printed circuit board (PCB) is fed into the printing machine for solder paste coating, it must be securely fixed within the machine. There are generally two methods to stabilize the PCB in the printer: the first involves using a conveying and positioning guide rail; the second relies on vacuum suction to secure the bottom of the conveying guide.
For thin and fragile printed circuit boards, if the first method is employed, we may encounter issues. Once the PCB is placed on the transfer rail of the printing machine and positioned correctly, the two transfer rails will clamp the PCB together. This can cause the middle section of the PCB to slightly bulge. This clamping force not only risks damaging the PCB but also results in the board being raised in the center, leading to uneven coating across the entire surface. Such inconsistencies can significantly impact the quality of the solder paste application.
1. If solder paste is applied using the second fixed printed circuit board (PCB) method, the issues mentioned earlier can be avoided. In this approach, the conveying rails do not face each other, eliminating opposing forces on the PCB’s sides, which prevents any bulging in the middle. This printer utilizes a vacuum suction device beneath the conveying rail to securely hold the PCB, preventing breakage from external clamping forces. Additionally, the PCB is suspended in the middle, so to maintain a flat, unbent surface during coating, we will incorporate a custom platform within the vacuum suction device to support the PCB during operation. This platform’s area is tailored to the PCB size, effectively addressing the issue of an uneven surface that could impact coating quality.
2. To ensure yield and product quality, the second type of printing with vacuum adsorption and fixation is utilized in production. After solder paste application, the PCB moves to the placement process. Before entering the placement machine, the PCB must be secured. Typically, there are two methods for clamping: the first involves moving the transfer rails on the placement platform toward each other to fix and position the PCB; the second utilizes a compression strip on the rail that automatically presses down on the PCB as it reaches the designated spot, securing both sides against the guide rail. Regardless of the method used, the absence of bottom support results in suspension, which poses a risk for thin PCBs that may break during placement. With movement during the placement process, ensuring the PCB surface remains flat is challenging, potentially compromising chip placement accuracy.
3. Furthermore, the first PCB method poses risks for thin, fragile boards, as the opposing clamping forces can easily cause bulging in the center. For PCBs with jigsaw patterns, this could lead to joint breakage. To mitigate this, we secure the PCB in a custom-made tray that is sent along the conveyor rail into the placement machine, thus shielding it from direct external forces. This tray provides necessary support, preventing deformation during placement and ensuring placement accuracy. This approach necessitates good consistency among the trays, including their shape, frame, size, and PCB positioning parameters, as inconsistencies can directly affect placement accuracy.
4. However, this method is not without its flaws. It demands high standards for pallet manufacturing, particularly in terms of consistency, while also addressing the challenge of securing the PCB within the tray. It is essential to ensure that the PCB remains stable in the pallet while allowing for easy handling, which complicates and increases the cost of pallet production. To address these issues, we propose an alternative solution: designing the pallet as a simple frame that uses vacuum adsorption to secure the PCB. This simplifies tray manufacturing while maintaining consistency and facilitating PCB handling. However, this solution requires slight modifications to the existing placement machine, as it currently lacks vacuum adsorption capabilities. Thus, a small vacuum device must be integrated, with its pump synchronized to the conveying rail’s movement to properly clamp and secure the PCB.
