The MARK point is the position identification point on the automatic placement machine used by the PCB in the design, and is also called the reference point. The diameter is 1MM. The stencil mark point is the position identification point when the PCB is printed with solder paste/red glue in the circuit board placement process. The selection of Mark points directly affects the printing efficiency of the stencil and ensures that the SMT equipment can accurately locate the PCB board components. Therefore, the MARK point is very important for SMT production.
① MARK point: SMT production equipment uses this point to automatically locate the position of the PCB board, which must be designed when designing the PCB board. Otherwise, SMT is difficult to produce, or even impossible to produce.
1. It is recommended to design the MARK point as a circle or a square parallel to the edge of the board. The circle is the best. The diameter of the circular MARK point is generally 1.0mm, 1.5mm, 2.0mm. It is recommended that the design diameter of the MARK point is 1.0mm. If the size is too small, the MARK dots produced by PCB manufacturers are not flat, the MARK dots are not easily recognized by the machine or the recognition accuracy is poor, which will affect the accuracy of printing and placement components. If it is too large, it will exceed the window size recognized by the machine, especially the DEK screen printer) ；
2. The position of the MARK point is generally designed on the opposite corner of the PCB board. The MARK point must be at least 5mm away from the edge of the board, otherwise the MARK point will be easily clamped by the machine clamping device, causing the machine camera to fail to capture the MARK point;
3. Try not to design the position of the MARK point to be symmetrical. The main purpose is to prevent the operator’s carelessness in the production process from causing the PCB to be reversed, resulting in incorrect placement of the machine and loss of production;
4. Do not have similar test points or pads in the space of at least 5mm around the MARK point, otherwise, the machine will misidentify the MARK point, which will cause loss to production;
② Position of via design: Improper via design will cause less tin or even empty soldering in SMT production welding, which will seriously affect the reliability of the product. It is recommended that designers do not design on the pads when designing vias. When the via hole is designed around the pad, it is recommended that the edge of the via hole and the pad edge around the ordinary resistor, capacitor, inductance, and magnetic bead pad should be kept at least 0.15mm or more. Other ICs, SOTs, large inductors, electrolytic capacitors, etc. The edges of the vias and pads around the pads of diodes, connectors, etc. are kept at least 0.5mm or more (because the size of these components will be expanded when the stencil is designed) to prevent the solder paste from losing through the vias when the components are reflowed ；
③ When designing the circuit, pay attention to the width of the circuit connecting the pad not to exceed the width of the pad, otherwise, some fine-pitch components are easy to be connected or soldered and less tinned. When the adjacent pins of IC components are used for grounding, it is recommended that designers not design them on a large pad, so that the design of SMT soldering is not easy to control;
Due to the wide variety of components, only the pad sizes of most standard components and some non-standard components are currently regulated. In the future work, we will continue to do this part of the work, service design and manufacturing, in order to achieve everyone’s satisfaction. .