1、 Process edge
The PCB process edge, also known as the working edge, is a long strip blank board edge set up to reserve track transmission positions and place assembly mark points during SMT. The width of the process edge is generally 5-8mm. Some people, in order to save some PCB costs, do not make process edges or set the process edges to 3mm, which is not advisable.
Under what circumstances can the process edge be cancelled? When your PCB has a regular rectangular shape for easy rail transmission, and the shape of the SMD component closest to the board edge is more than 5mm away from the board edge, you can cancel the process edge. Alternatively, if your PCB is similar to a mobile phone board (with hundreds of SMT components on a single chip board, and the PCB is an expensive multi-layer board with a continuous high product volume), you can cancel it and have the SMT factory spend thousands of yuan on a one-time fixture to replace the continuous cost expenditure during the process.
PCB process edges are generally set by PCB factories, and designers can inspect them according to the following key points:
1. Width 5-8mm;
2. The mark points placed on it are standardized and reasonable;
3. The support and connection of the PCB are stable and reliable, enabling stable transmission of the PCB on the track;
2、 MARK point
The Mark point, also known as an optical reference point, is a measurable reference point set for various assembly steps to compensate for PCB manufacturing errors and equipment positioning errors. The production process of PCB boards determines that the accuracy of circuit graphics is one to two orders of magnitude higher than the accuracy of appearance and drilling. Mark points are essentially part of the circuit graphics. Using Mark points as the identification and positioning benchmark for SMT equipment can automatically correct various deviations and eliminate errors. Therefore, Mark is crucial for SMT production.
The shape of Mark points is generally a solid circle. The setting method is as follows: Set a component (the advantage of using the Mark point as a component is that when exporting component coordinates, the Mark point coordinates are also exported, and the Mark point coordinates are very important). The component is a solid circular pad with a pad diameter of 1mm and a solder mask window diameter of 3mm. Solid circles require a clean and flat surface, smooth and neat edges, and distinct colors from the surrounding background. The surface should be treated with gold deposition, and the 3mm solder mask window should be kept blank. No solder pads, holes, wiring, solder mask ink, or screen markings are allowed to create a high contrast between the Mark points and the substrate of the PCB board.
The Mark points are located on the four diagonal corners of the circuit board or assembly process edge, but the Mark points set around the board cannot be symmetrical to prevent the machine from recognizing the situation where the board is placed upside down (unable to prevent fooling). As shown in the following figure, just place one of the four Mark points about 1cm away from each other.
