PCB News - How to set grid points in PCB design

Reasonable use of the grid system can enable us to play a multiplier role in PCB design. But what is reasonable?

Many people think that the smaller the grid point is, the better. In fact, it is not. Here we mainly talk about two aspects: the first is the selection of grid points in different stages of design, and the second is the selection of different grid points for wiring. Of course, the grid setting needs to be flexibly grasped in practical applications. The copying of the text and the use of dogma are not allowed.

Different grid settings are required in different stages of design. In the layout stage, large grid points can be used for device layout; for large devices such as ICs and non-positioned connectors, a grid point accuracy of 50 to 100 mils can be used for layout, and for small passive components such as resistance-capacitance and inductance, a grid point of 25 mils can be used. Make the layout. The accuracy of the large grid points is conducive to the aesthetics of device alignment and layout. In the design with BGA, if the 1.27mm BGA is used, then we can set the grid point accuracy to 25mil when fanout is used, which is conducive to the fanout vias being exactly at the center of the four pins; for 1.0mm and 0. For 8mm BGA, we'd better use mm units for layout, so that the fanout vias can be set up well. For fanouts of other ICs, it is also recommended to design with large grid points. We recommend that the grid point of fanout should be 50mil or even larger. It is best if it can be ensured that wires can be routed between every two vias.

The grid point in the wiring stage can be 5mil (not necessarily). Remember not to set a 1mil wiring grid point, this will make the wiring very cumbersome and time-consuming. Now we talk about why it is recommended to use 5mil (or other grid points) design accuracy in wiring design. Usually there are two factors to determine the design grid: the line width factor and the line spacing factor. In order to match our design accuracy with our design, there can be a simple formula as follows: (line width + line spacing) /5=n, where n must be an integer greater than 1. From the actual design, the line width + line spacing can be greater than 10. Take 15 as an example. So when the line width is 6 mils, the line spacing is 9 mils; when the line width is 7 mils, the line spacing is 8 mils. Only in this way can we use the grid accuracy to ensure the correctness of the design rules during design adjustments. It is better to use more than 25mil for the grid points of the vias during wiring. We can achieve different grid points for wiring and vias by setting the size of the grid in ALLEGRO. In this way, large grid points and small wiring grid points can be achieved.

The above is an introduction to how to set grid points in PCB design. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology.