The Mark point is the position identification point where the PCB is used on the automatic placement machine in circuit board design. It is also called the reference point. The diameter is generally 1.0mm. Mark points provide a common, positionable circuit pattern for all steps in the assembly process, which is crucial for SMT production.
Classification and functions of Mark points
According to the role of Mark points on PCB, they can be divided into single board Mark points, panel Mark points and local Mark points.
1. Single board Mark, its function is to locate the positions of all circuit features on a single board, which is essential;
2. Puzzle Mark, which is used to assist in locating the positions of all circuit features on the puzzle board and assisting in positioning;
3. Local Mark, which is used to locate the reference point mark of a single component to improve placement accuracy (important components such as QFP, CSP, BGA, etc. must have local Mark), which is essential.
Precautions:
1. There should be at least one pair of Mark points on each surface of the PCB board located in the diagonal direction of the PCB board, with the relative distance as far as possible. There should be at least three Marks on the process side of the panel and on the single board that does not require panelization. Points are distributed in an L shape, and the diagonal Mark points are asymmetrical about the center (to prevent stupidity).
2. For a rectangle with two Mark points as diagonal vertices, the more components it contains, the better.
3. If there are mounted components on both sides, there should be Mark points on each side.
Mark point design
1. The shape of the Mark point is a solid circle with a diameter of 1mm. The material is copper and the surface is sprayed with tin. Pay attention to the flatness, the edges are smooth and neat, and the color is obviously different from the surrounding background color; the solder mask window is concentric with the Mark point. , the diameter is 3mm for puzzle pieces and single boards, and the diameter for local Mark points is 1mm.
2. The distance between the edge of the Mark point and the edge of the PCB board is at least 3.5mm (the center of the circle is at least 4mm from the edge of the board). The distance between the Mark point and other metal dots of the same type (such as test points, etc.) should not be less than 5mm.
3. In order to ensure the recognition effect of printing and patching, there should be no pads, vias, test points, traces, silk screen marks, etc. within the Mark point range, and it should not be cut by the V-CUT slot, causing the machine to be unable to identify it. If the mark point is made on the copper foil, it must be isolated from the copper foil.
4. If there is no place to add Mark points on the single board, you need to add a 5MM process edge and add Mark points on the process edge.
