The rule of vertical routing means that the leads in adjacent signal layers need to be perpendicular to each other to reduce the crosstalk caused by mutual inductance. In high-frequency signals, crosstalk generated by capacitive coupling accounts for the main component, generating current spikes between the vertical leads.
When the signal changes along time, or at lower frequencies (less than a few GHz), the coupling capacitance of adjacent signal layer vertical wiring pieces interferes little. In the radio frequency (RF) band (tens of GHz), the interweaving between the leads produces cavity resonance, and not surrounded by ground conductor structure will produce electromagnetic resonance at some special frequency points. At this point, even if the leads are perpendicular to each other, it will also cause strong crosstalk between them.
In order to eliminate interference at all frequency points, a simple and effective method is to use multilayer boards and use isolation layers between signal layers. This is especially important in contemporary applications where signals change at high speeds. When you are not sure about the strength of coupling between orthogonal lines, you need to use the basic crosstalk simulation software to check the vertical leads to see if the crosstalk between them is within the noise tolerance range. At this point, you need more planning for the signal return path, which is a major issue in vertical wiring.
This is a classic "comply/avoid" rule, which often causes controversy. Some PCB designers say they never use to prevent thermal overshoot, and never encounter problems with soldering and assembly. While another group of people insist on preventing thermal vias need to be used when every plane is connected. Who are they right?
Their views are applicable to different situations. If you manually solder the board, you need to raise the temperature of the soldering iron tip to compensate for the soldering over-hole in the copper layer heat dissipation brought about by the soldering problem. But if you use wave soldering, you need to use the prevention of heat dissipation over-hole to prevent device loosening, cold soldering, standing monument and other phenomena, so I suggest you better bite the bullet and insist on using the prevention of heat dissipation over-hole design.
This PCB wiring rules are perhaps the most loved and hated. Today I still see many PCB designers insist that at no time wiring can not turn right angles, and the reasons are varied. For example, they say that the electrons in the lead movement when turning right-angle bends difficult, but they do not think about it, all the holes on the board can be perpendicular to the lead ah. Some reasons seem more reliable, such as by 45 ° corner can reduce the lead length, all right-angle corner wiring need to be chamfered. Others say that right-angle corners will produce acid corrosion traps in the board acidic etching solution, in the now widely used alkaline board etching solution is not the problem.
Unless your board is working at high frequencies above 50GHz (involving millimeter wave radar/5G communications) circuitry, you don't need to worry about right-angle lead turns. In fact, you can use any angle you like when routing the board to lay the leads. If you are using the PCB design software built-in electromagnetic field solver function which makes your wiring easier.
That is, the three wiring rules of thumb. The first version of the "3W" rule is that the interval between two adjacent leads should be greater than or equal to three times the width of the lead, in order to reduce the magnetic flux coupling between the leads, which reduces the electromagnetic interference between the leads.
This rule may forget that the electromagnetic coupling between the leads is proportional to the overlapping area of the lead loops, not the distance between the leads; therefore, by reducing the overlapping area of the lead loops, the lead spacing is not limited by the 3W rule. As with vertical wiring, the basic EMI simulation allows you to examine the effects of different wiring spacing.
Another version of the "3W" rule refers to the sawtooth wiring used in lead length matching, where the width of the sawtooth needs to be greater than or equal to three times the lead width, which minimizes the discontinuity of the lead impedance.
This rule defines the PCB ground layer and power layer overlap distance between the modern PCB design needs to lay the power supply in the vicinity of the ground, which can ensure that they have sufficient interlayer capacitance, which in turn reduces power fluctuations on high-speed circuit boards.
But the actual measurement results will find the results are complex. Some time results standard name at 300MHz to comply with the 20H rule can reduce electromagnetic radiation. But between the ground - power supply layer will appear high-frequency resonance, they are similar in structure to waveguide, but will instead aggravate the high-frequency interference between the lines.