PCB News - Precautions for PCB design novices

1. Single-sided pad:

Do not use filler blocks as the pads of surface mount components. Single-sided pads should be used. Normally, single-sided pads are not drilled, so the aperture should be set to 0.

2. Vias and pads:

Do not replace vias with pads, and vice versa.

3. The expression of metallized holes and non-metallized holes:

Generally, the multilayer pad holes that are not explained in any way will be metalized. If you do not want to metalize the holes, please mark them on the Mech1 layer with arrows and text. For irregular holes, square grooves, square holes, etc. in the board, if the edges are surrounded by copper foil, please indicate whether the holes are metallized. Conventional bottom holes are as large as the pads or holes without pads and without electrical properties are regarded as non-metallized holes.

4. The relationship between the setting of the hole diameter and the minimum value of the pad:

Generally, the component foot diameter, pad diameter, via hole diameter and via hole diameter should be considered when placing components in the early stage of wiring, so as to avoid the inconvenience caused by modifying the wiring after wiring. If the finished hole diameter of the component pad is set to X mil, the pad diameter should be set to ≥X+18mil.

5. Requirements for copper paving area:

Whether the large area copper paving is made into grid or solid copper, the distance from the edge of the board is required to be greater than 0.5mm. The copper-free grid point size of the grid is required to be greater than 15mil*15mil, that is, in the Plane Settings window of the grid parameter setting window

(Grid Size value)-(Track Width value) ≥15mil, Track Width value ≥10, if the grid has no copper grid points less than 15mil*15mil, it is easy to cause other parts of the circuit board to open during production. At this time, the copper should be laid and set Certainly:

(Grid Size value)-(Track Width value)≤-1mil.

6. Requirements for solder mask green oil:

A. For all designs according to specifications, the solder joints of the components are represented by pads. These pads (including vias) will automatically not be solder masked, but if you use filler blocks as surface pads or wire segments as gold finger plugs Without special treatment, the solder mask will cover these pads and golden fingers, which is easy to cause misunderstanding errors.

B. Except for the pads on the circuit board, if you need some areas without solder mask (ie special solder mask), they should be on the corresponding layer (the top layer is drawn on the Top Solder Mark layer, and the bottom layer is drawn on the Bottom On the Solder Mask layer) use solid graphics to express the areas where solder mask ink is not to be applied. For example, if you want to expose a rectangular area on a large copper surface of the Top layer, you can draw this solid rectangle directly on the Top Solder Mask layer, without editing a single-sided pad to express the solder mask ink.

C. For BGA boards, the via pads next to the BGA pads must be covered with green oil on the component surface.

7. Expression of appearance:

The outline processing drawing should be drawn on the Mech1 layer. If there are special-shaped holes, square grooves, square holes, etc. in the board, also drawn on the Mech1 layer. It is best to write the word CUT and the size in the groove. When drawing square holes, square grooves, etc. The turning point and the arc of the end point should be considered when the contour line is processed. Because it is processed by a CNC milling machine, the diameter of the milling cutter is generally φ2.4mm, and the minimum is not less than φ1.2mm. If the 1/4 arc is not used to indicate the turning point and the end fillet, it should be marked with an arrow on the Mech1 layer, and at the same time, please mark the tolerance range of the final shape.

8. The expression of the long hole on the pad:

The hole diameter of the pad should be set to the width of the long hole, and the outline of the long hole should be drawn on the Mech1 layer. Note that the two ends are arcs and consider the installation size.

9. How to set the hole size when the component feet are square:

Generally, when the side length of the square pin is less than 3mm, it can be assembled with a round hole. The hole diameter should be set slightly larger than the diagonal value of the square (considering the dynamic fit). For larger square feet, the outline of the square hole should be drawn in Mech1.

10. When multiple different boards are drawn in one file, and you want to divide the delivery, please draw a frame for each board on the Mech1 layer, and leave a space of 100mil between the PCB boards.

11. Text requirements:

Character labeling should be avoided as much as possible, especially the soldering pads of surface mount components and the soldering pads on the Bottem layer, and there should be no characters and labels printed. If the actual space is too small to fit the characters and need to be placed on the pad, and there is no special statement whether to retain the characters, we will cut off any part of the upper pad on the Bottem layer (not the entire character) and cut off when making the board. The character part on the pad of the surface mount component on the TOP layer to ensure the reliability of soldering. If the characters are printed on the large copper skin, the characters are printed after the tin is sprayed, and the characters are not cut. All characters outside the board are deleted.

The above is an introduction to the precautions for PCB designnovices. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology