source:Industry News release time:2023-04-07 Article author:yu Popular:pcb
When the PCB is encapsulated in PCB, the problem of poor grasping the pads often encounters the problem of poor grasping pads, because the information we consider is the size of the component itself, such as the width of the pin, the spacing, etc., but on the PCB board, but on the PCB board, etc. The corresponding pads should be slightly larger than the size of the pin, otherwise the reliability of welding will not be guaranteed. The following will mainly talk about the norms of the pad size.
In order to ensure the welding quality of the patch component (SMT), when designing the SMT printing board, except for the printed board, the 3mm-8mm process should be left out. In addition to the distance between the orientation of the meta component and the distance between the adjacent components, we believe that we should pay special attention to the following points:
(1) On the printed board, any of the conductive graphics (such as interconnection, grounding, interoperability panel, etc.) and the copper foil that are required should be nude copper foil. That is, the metal coating that is not allowed to be plated than the welding temperature, such as tin lead alloys, etc., to avoid causing the welding membrane at the coating layer to break or wrinkle to ensure the welding and appearance of the PCB board.
(2) When checking or calling the graphic size data of the pad, it should be matched with the size of the encapsulated shape, solder end, pins, etc. of the components you selected. It is necessary to overcome the bad habits of the graphic size of the pad in the software library that you see without analysis or control or call. When designing, selected or calling the graphic size of the pad, you should also distinguish the components you chose, its code (such as chip resistance, capacitance) and welding -related dimensions (such as SOIC, QFP, etc.).
(3) The welding reliability of the surface -sticker component depends mainly on the length of the pad rather than width.
(A) As shown in Figure 1, the length B of the pads is equal to the length T of the weld (or pin), plus the extension length B1 of the inner side (pad) of the weld (or pin) (Or pins) extension length B2, which is B = T+B1+B2. Among them, the length of B1 (about 0.05mm -0.6mm) should not only benefit the welding joints that can form a good moon -shaped outline when welded melting, but also to avoid the phenomenon of bridge and the installation deviation of the components. ; The length of B2 (about 0.25mm -1.5mm), mainly to ensure that the best welding joints that can form the best moon -shaped outline are advocated (for SOIC, QFP and other devices, it should also take into account the ability of its pads to resist and peeling).)
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