After explaining the PCB wiring after the completion of the inspection work, first for everyone to introduce three kinds of PCB special alignment skills. Will be from the right angle alignment, differential alignment, serpentine line to explain the three aspects of PCB LAYOUT alignment:

One, right-sided alignment (three aspects)

Right angle alignment of the signal is mainly reflected in three aspects: First, the corner can be equivalent to the transmission line on the capacitive load, slow rise time; Second, the impedance will cause a continuous reflection of the signal; Third, Of EMI, to 10GHz above the RF design field, these small right angles may become a high-speed problem of key objects.

Second, the differential alignment ("equal length, equidistant, reference plane")

What is the differential signal? Differential? The vulgar is the drive side to send two equivalent, inverted signal, the receiver by comparing the difference between the two voltage to determine the logic state "0" or "1". And the pair of traces that carry the differential signal are called differential traces. Differential signal and ordinary single-ended signal traces compared to the most obvious advantages are reflected in the following three aspects:

1) strong anti-interference ability, because the coupling between the two differential traces is very good, when there is noise outside the interference, almost simultaneously coupled to the two lines, and the receiver is only concerned about the difference between the two signals, So the external common mode noise can be completely offset.

2) can effectively suppress EMI, the same reason, because the polarity of the two signals on the contrary, their external radiation electromagnetic field can offset each other, the closer the coupling, the less the electromagnetic energy released to the outside world.

3) timing positioning accuracy, because the differential signal switching is located at the intersection of two signals, rather than ordinary single-ended signal to rely on the level of the two threshold voltage to determine, and thus by the process, the temperature is small, can reduce the timing error , But also more suitable for low-amplitude signal circuit. The current popular LVDS (low voltage differential signaling) refers to this small amplitude differential signal technology.

Three, serpentine line (adjustment delay)

The serpentine line is a type of tracing that is often used in Layout. Its main purpose is to adjust the delay to meet the system timing design requirements. The most critical of the two parameters is the parallel coupling length (Lp) and the coupling distance (S), it is clear that the signal in the serpentine line transmission, parallel to each other between the lines will be coupled, was differential mode, S The smaller the Lp, the greater the degree of coupling. May lead to reduced transmission delay, and due to crosstalk and greatly reduce the quality of the signal, the mechanism can refer to the common mode and differential mode crosstalk analysis. Here are a few suggestions when the layout engineer handles the serpentine line:

1) As much as possible to increase the distance (S) of the parallel line segment, at least greater than 3H, H refers to the distance from the signal trace to the reference plane. Popular say is around the big bend line, as long as S is large enough to almost completely avoid mutual coupling effect.

2) reduce the coupling length Lp, when the double Lp delay close to or exceed the signal rise time, the resulting crosstalk will reach saturation.

3) Strip-line or embedded Micro-strip snake lines cause signal transmission delay less than microstrip (Micro-strip). In theory, the stripline does not affect the transmission rate due to differential mode crosstalk.

4) high-speed and timing requirements of the more stringent signal lines, try not to go serpentine line, in particular, can not be in a small range of winding routes.

5) can often use any angle of the serpentine line, can effectively reduce the coupling between each other.

6) high-speed PCB design, the serpentine line does not have the so-called filtering or anti-jamming capability, can only reduce the signal quality, so only for timing matching with no other purpose.

7) Sometimes the spiral traces can be considered in the way of winding, simulation shows that the effect is better than the normal serpentine alignment.

PCB wiring, then the cloth line on the finished? Obviously, not! PCB wiring inspection work is also very necessary, then how to PCB design wiring inspection, later designed to pave the way? Look below!

General PCB design drawings check items

1) circuit analysis did not? In order to smooth the signal circuit is divided into the basic unit did not?

2) Does the circuit allow the use of short or isolated key leads?

3) must be shielded, effectively shielded it?

4) take full advantage of the basic grid graphics without?

5) Is the size of the printed circuit board the best size?

6) Do you want to use the selected wire width and spacing as much as possible?

7) Is the preferred pad size and hole size used?

8) Is the camera and the sketch appropriate?

9) Is the jumper used at least? Are jumper wires passing through components and attachments?

L0) After the assembly can see the letter? Its size and model is correct?

11) In order to prevent the bubble, a large area of ​​the copper foil to open the window did not?

12) Is there a tool positioning hole?