/During Pcb manufacturing, how to set up solder mask and wire screen ?
There are two methods for applying the solder mask layer, liquid silk screen solder mask coating method and photo solder resist coating method. The dimensional accuracy of the solder mask fenestration depends on the technological level of the printed board manufacturer. When the liquid screen solder mask coating method is used, the solder mask opening window size needs to be 0.4 mm larger than the pad size. When using the photo solder resist coating method, the solder mask opening window size needs to be 0.15 mm larger than the pad size. For the finest solder mask layer, the screen printing technique should have a 0.3mm gap, while the photolithography technique should have a 0.2mm gap.
(1) Solder mask
1PCB manufacturing generally chooses hot air leveling process.
2 The size of the solder mask pattern is 0.05~0.254mm larger than the perimeter of the pad to prevent the solder mask from contaminating the pad. 3 When there is no wire passing between narrow pitch or adjacent pads, the solder resist pattern can be designed by the method of Figure 1. When there is a wire between adjacent pads, in order to prevent solder bridging, the method of Figure 2 should be used to design solder mask graphics.
(2) screen graphics
In general, the screen pattern of the component needs to be marked on the screen layer. The screen pattern includes the screen symbol, the component number, the polarity, and the IC’s 1-pin mark, as shown in Figure 3(a). High density, narrow spacing can be used, with simplified symbols, as shown in Figure 3 (b). In special cases, the component number can be omitted. OSP pad coating should be noted: the thickness of the simplified screen should not exceed the pad, otherwise it will easily pick up from one end of the component.
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