Common PCB Design Issues and Solutions for Circuit Board Novice(Part Two)

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PCB Design
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pcb design issue, pcb board, pcb,pcb design tutorial,pcb design knowledge
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Common PCB Design Issues and Solutions for Circuit Board Novice

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Catalogs
I.High speed PCB design, the distribution of copper in multiple signal layers in the distribution of grounding and power supply
II.Two commonly referred characteristic impedance formulas 
III.Can the testing point in high density PCB automatically generate test points by software can meet the requirements of mass production in general?
IV.Effects of adding test points on high speed signal quality
V.A system composed of several PCB, the connection between the ground lines of each board
VI.The signal lines on the power plane can use the microstrip line model to calculate the characteristic impedance; the signal between the power and the ground plane can also be calculated using a strip line model
VII.The selection principle of ground point for PCB and shell
VIII.Based on the IPC6013 standard Adagio
IX.The ground line in the middle of the differential signal line is generally not added
X.Three aspects of the road board DEBUG?
XI.Relevant information about "Common PCB Design Issues and Solutions for Circuit Board Novice(Part Two)"


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I.High speed PCB design, the distribution of copper in multiple signal layers in the distribution of grounding and power supply

Generally, most of the application of copper in the blank area is grounding. Just pay attention to the distance between the copper and the signal line when the copper is applied to the high speed signal line, because the copper applied will reduce the characteristic impedance of a little walk line. Also, be careful not to affect the characteristic impedance of its layer, such as the structure of dual stripline.

II.Two commonly referred characteristic impedance formulas

A. microstrip
Z={87/[sqrt (Er+1.41)]}ln[5.98H/ (0.8W+T)], where W is the line width, T is the thickness of copper skin, H is the distance from the line to the reference plane, Er is the dielectric constant of dielectric constant. This formula must be applied in the case of 0.1< (W/H) <2.0 and 1< (Er) <15.

B. stripline
Z=[60/sqrt (Er)]ln{4H/[0.67 PI (T+0.8W)]} the H two reference plane distance, intermediate and walk line at two reference plane. This formula must be applied in the case of W/H<0.35 and T/H<0.25.

III.Can the testing point in high density PCB automatically generate test points by software can meet the requirements of mass production in general?

The general software automatically generates test points to meet the testing requirements. It is necessary to see whether the specification of the added test points meets the requirements of the testing machine. In addition, if the line is too dense and the specification of the test point is relatively strict, it may not be possible to automatically add test points to each line. Of course, it is necessary to manually fill the testing area.

IV.Effects of adding test points on high speed signal quality

As to whether the quality of the signal will affect the quality of the signal, it depends on how fast and how fast the signal is added to the test point. Basically an additional test point (not using an existing via or DIP pin) as a test point may be added online or out of a small line from the line. The former is equivalent to a very small capacitance on line, and the latter is a branch. These two conditions will have a little or less impact on high speed signals, and the extent of the impact is related to the frequency of the signal and the rate of change of the edge rate. The impact size can be learned through simulation. In principle, the smaller the better the test points (and of course, to meet the requirements of the test machine), the shorter the better the branch.

V.A system composed of several PCB, the connection between the ground lines of each board

When the signal or power supply between each PCB board is interconnected, for example, the A board has power or signal to the B board, there will be equal amount of current flowing back to the A board from the stratum flow (this is Kirchoff current law). The current in this stratum will flow back where the impedance is minimized. Therefore, the number of pins allocated to the formation can not be too low at all interfaces, which are connected with the power or signal, so as to reduce the impedance, which can reduce the noise on the stratum. In addition, can also analyze the current loop, especially the larger part of the current adjustment, the formation or wire connecting method, to control the current law (for example, somewhere in the low impedance, make the most of the current from the place to go), to reduce the influence of other sensitive signal.

VI.The signal lines on the power plane can use the microstrip line model to calculate the characteristic impedance; the signal between the power and the ground plane can also be calculated using a strip line model

The signal line on the power plane can be used to calculate the characteristic impedance using the microstrip line model, and the signal between the power and ground plane can also be calculated by the strip line model. Both the power plane and the ground plane must be considered as the reference plane when the characteristic impedance is calculated. For example, four laminates: the top layer - the power layer - the stratum - bottom, and the model of the characteristic impedance of the top - level walking line is the microstrip line model with the power plane as the reference plane.

VII.The selection principle of ground point for PCB and shell

The principle of selecting the location of PCB and shell is to use chassis ground to provide low impedance path to return current (returning current) and control the path of reflux current. For example, usually in the vicinity of high-frequency devices or clock generators, we can connect the stratum of PCB with chassis ground by means of fixed screws, so as to minimize the area of the whole current circuit and reduce the electromagnetic radiation.

VIII.Based on the IPC6013 standard Adagio

Common PCB Design Issues and Solutions for Circuit Board Novice(Part Two)

The flexible circuit board (Flexible Printed Circuit) can be designed with the software of the general design of PCB. The same is used in Gerber format for the production of FPC manufacturers. Due to the difference between the manufacturing process and the general PCB, each manufacturer will have limitations on the minimum Xian Kuan, the minimum line distance and the minimum Kong Jing (via) based on their manufacturing capability. In addition, some copper skin can be made up at the turning point of the flexible circuit board. The inspection standard of the soft board is usually based on IPC6013.

IX.The ground line in the middle of the differential signal line is generally not added

In the middle of the differential signal, the ground line can not be added. Because the most important thing is the advantage of differential signal coupling (coupling), such as flux cancellation, anti noise (noise immunity), etc. If the ground wire is added in the middle, the coupling effect will be destroyed.

X.Three aspects of the road board DEBUG?

As far as digital circuits are concerned, three things are first determined in sequence:
(1) it is confirmed that all power supply values are required for the design. Some systems with multiple power sources may require some specification of the order and speed between some power sources.
(2) it is confirmed that all clock signal frequencies are working normally and there is no nonmonotone (non-monotonic) problem on the edge of the signal.
(3) confirm whether the reset signal has reached the standard requirements.
If these are normal, the chip should send out the signal of the first cycle (cycle). Then come to debug according to the operating principle of the system and bus protocol.

The above is the Common PCB Design Issues and Solutions for Circuit Board Novice(Part Two), next issue: the Common PCB Design Issues and Solutions for Circuit Board Novice(Part Three) welcome to follow me!

XI.Relevant information about "Common PCB Design Issues and Solutions for Circuit Board Novice(Part Two)"
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