1. Stencil opening considerations

1) A single pad cannot be larger than 3 * 4MM, and a larger one should be reinforced 0.2-0.3MM

2) All pad opening round size should not be less than 0.05MM

3) Pay attention to the safety distance when expanding, generally 0.25MM

4) The MARK point is in principle the same as the PCB size. When the diameter exceeds 1.5MM, it needs to be confirmed.

5) All openings must not exceed the edge of the PCB, 0.2MM inside the edge

6) The pad is one big and one small phenomenon. If the tin plate is a PCB design phenomenon, it should be opened by one big and one small . If it is caused by solder mask printing, it should be opened according to the small one; the copper plate should be opened one big and one small.

7) When the original pad has a large internal distance, but it needs to be attached with a small distance in the soldering position, it is generally made into a way of pulling and then cutting the pad, which not only ensures good soldering, but also achieves the effect of anti-tin beads.

8) When the original PAD of the CHIP part is square, the anti-tin beads should pay attention to the direction.

2. SMT stencil opening size and PCB pad size comparison

1) The general design standard states that the opening size should be reduced correspondingly to the PCB pad.

2) When using no-clean solder paste, the opening size of the template should be reduced by 5%-10% when using the no-clean process.

3) Reducing the area and correcting the shape of the opening is usually to improve the printing quality of the solder paste. The reflow process and the stencil are cleaner in the solder paste printing process, which helps to reduce the chance of the solder paste printing deviating from the pad.

4) In the absence of a narrow pitch, the shape and size of the opening of the template may be the same as the corresponding pad.

5) Rounding all the holes can promote the cleanliness of the template.

6) Appropriate opening shape can improve the placement effect. Printing off the pad can easily lead to solder beads and bridging. The template opening is usually changed compared to the original PCB pad.