CN100471365C - Method for printed circuit board wiring and printed circuit board - Google Patents

Abstract

The invention relates to a wiring method of printed circuit board and relative printed circuit board. Wherein, said printed circuit board has several receivers; the pin welding discs of receivers are connected via transmission wires; and the inventive method comprises distributing one fine transmission wire between the pin welding disc and the transmission wire, whose one end is connected to pin welding disc and another end is connected to the transmission wire; therefore, the capacitor of pin is distributed to the fine transmission wire whose length can be controlled to make the resistance of fine transmission wire equal to the resistance of thick transmission wire at other places; especially when the fine transmission wires at two ends of pin are at same lengths, the capacity of pin can be uniformly distributed to the fine transmission wire.

Description

A kind of wiring method of printed circuit board (PCB) and printed circuit board (PCB)

Technical field

The invention belongs to the print circuit plates making field, relate in particular to a kind of wiring method and printed circuit board (PCB) of printed circuit board (PCB).

Background technology

The speed of chip is more and more higher, and (Print Circuit Board, cabling requirement PCB) is also more and more higher to printed circuit board (PCB).When transmitting on the cabling of signal at pcb board, if matching, impedance will not produce reflection, the circuit theory of a unmatched pcb board of impedance as shown in Figure 1, from left to right be followed successively by driver, first receiving device, second receiving device and four devices of the 3rd receiving device, connect by transmission line between the pin pad of device, its wiring on pcb board as shown in Figure 2.When the impedance of all transmission lines is 33 ohm, when the speed of driver is 500Mhz, simulation waveform as shown in Figure 3, waveform from left to right is followed successively by driver, first receiving device, second receiving device and the 3rd receiving device.As can be seen, because impedance does not match and causes signal reflex, waveform superposes, and high level is more and more higher, surpasses the level that chip can bear.

Existing a kind of scheme increases build-out resistor by the end at network and eliminates reflection, and as shown in Figure 4, when the resistance of resistance was 33 ohm, simulation waveform as shown in Figure 5.Comparison diagram 3 reflects and has reduced much as can be seen.

Yet, because all there is certain electric capacity in each Chip Packaging, this electric capacity is added in and will makes the impedance that becomes of the continuous transmission line of original impedance discontinuous on the cabling of pcb board, though above-mentioned mode by resistors match can be eliminated end reflection, but can not eliminate the discontinuous reflection that produces of the impedance that brings owing to Chip Packaging electric capacity, for example the waveform of first receiving device has obvious distortion among Fig. 5 when descending, and from left to right waveform is followed successively by driver, first receiving device, second receiving device and the 3rd receiving device among the figure.This distortion makes the significant level narrowed width, and the receiving device erroneous judgement can cause error in data.

Summary of the invention

The object of the present invention is to provide a kind of wiring method of printed circuit board (PCB), be intended to solve the discontinuous problem that produces reflection of the impedance that brings owing to Chip Packaging electric capacity that exists in the prior art.

Another object of the present invention is to provide a kind of printed circuit board (PCB).

The present invention is achieved in that a kind of wiring method of printed circuit board (PCB), and described printed circuit board (PCB) is provided with a plurality of receiving devices, connects by transmission line between the pin pad of described receiving device, and described method comprises:

Cloth one thin transmission line between the pin pad of described receiving device and described transmission line, the pin pad of the described receiving device of a termination of described thin transmission line, the described transmission line of another termination.

The length of described thin transmission line is pressed following formula and is determined:

$E_p=\frac{C_I{L}_u}{C_u{L}_t-C_t{L}_u};$

Wherein, C _IBe the pin electric capacity of described receiving device, L _uAnd C _uBe distributed inductance on the described transmission line and distributed capacitance, L _tAnd C _tBe distributed inductance and the distributed capacitance on the described thin transmission line.

The length of the thin transmission line at the pin pad two ends of described receiving device is isometric.

A kind of printed circuit board (PCB), described printed circuit board (PCB) is provided with a plurality of receiving devices, connect by transmission line between the pin pad of described receiving device, be furnished with a thin transmission line between the pin pad of described receiving device and the described transmission line, the pin pad of the described receiving device of one termination of described thin transmission line, the described transmission line of another termination.

The length of described thin transmission line is pressed following formula and is determined:

$E_p=\frac{C_I{L}_u}{C_u{L}_t-C_t{L}_u};$

Wherein, C _IBe the pin electric capacity of described receiving device, L _uAnd C _uBe distributed inductance on the described transmission line and distributed capacitance, L _tAnd C _tBe distributed inductance and the distributed capacitance on the described thin transmission line.

The length of the thin transmission line at the pin pad two ends of described receiving device is isometric.

The present invention is by cloth one thin transmission line on the pin pad of receiving device, with the capacitance profile on the pin of receiving device to this thin transmission line, make the equiva lent impedance of this thin transmission line equate by the length of controlling this thin transmission line, realize impedance matching with the impedance of the thick transmission line in other places.Especially when the thin transmission line at the pin two ends of receiving device kept isometric, the electric capacity of the pin of receiving device more can Approximate Equivalent be evenly distributed on this thin transmission line.

Description of drawings

Fig. 1 is the circuit theory diagrams of the pcb board of prior art middle impedance when not matching;

Fig. 2 is the pcb board wiring diagram corresponding with the circuit theory of pcb board among Fig. 1;

Fig. 3 is the wave simulation figure of prior art middle impedance when not matching;

Fig. 4 is the pcb board circuit theory diagrams when network end-point increases build-out resistor in the prior art;

Fig. 5 is the wave simulation figure when network end-point increases build-out resistor in the prior art;

Fig. 6 is the circuit theory diagrams of the pcb board that provides in the one embodiment of the invention;

Fig. 7 is the present invention wave simulation figure corresponding with Fig. 6;

Fig. 8～9th, the process schematic diagram of pcb board wiring among the present invention.

Embodiment

In order to make purpose of the present invention, technical scheme and advantage clearer,, the present invention is further elaborated below in conjunction with drawings and Examples.Should be appreciated that specific embodiment described herein only in order to explanation the present invention, and be not used in qualification the present invention.

The present invention is by cloth one thin transmission line on the receiving device pin pad of pcb board, electric capacity on the pin of receiving device is evenly distributed on this thin transmission line, make the equiva lent impedance of thin transmission line equate by the length of controlling this thin transmission line, realize impedance matching with the impedance of the thick transmission line in other places.

Because all there is certain electric capacity in each Chip Packaging, this electric capacity is added in and will makes the impedance that becomes of the continuous transmission line of original impedance discontinuous on the cabling of pcb board.The present invention is at the pin pad of receiving device and be connected cloth one thin transmission line between the former transmission line on the pin pad of receiving device, the pin pad of one termination receiving device of thin transmission line, the former transmission line of another termination, can be similar to and regard as the capacitance profile on the pin of receiving device to thin transmission line, make the equiva lent impedance of thin transmission line become big.Impedance and the length of controlling thin transmission line can be so that carefully the equiva lent impedance of transmission line equate with impedances of other local thick transmission lines.

The impedance of supposing one section thick transmission line linking to each other with the pin pad of receiving device in original pcb board is:

$Z_u=\sqrt{L_u/C_u};$

Wherein, L _uAnd C _uBe distributed inductance and the distributed capacitance on the former thick transmission line of this pcb board.

For with the capacitance profile on the pin of receiving device to the cabling of pcb board and the impedance of one section newly-increased thin transmission line is:

$Z_t=\sqrt{L_t/C_t};$

Wherein, L _tAnd C _tBe distributed inductance and the distributed capacitance on the thin transmission line of this pcb board.

With the approximate distributed capacitance of seeing as of the pin electric capacity of receiving device, then the equiva lent impedance of the pin of receiving device and thin transmission line is:

$Z_{\mathrm{leff}}=\sqrt{L_t/(C_t+C_I/E_p)};$

Wherein, C _IBe the pin electric capacity of receiving device, E _pLength for thin transmission line.

Continuous in order to guarantee impedance, then require Zu=Zleff, thereby the length that calculates the newly-increased thin transmission line of pcb board is:

$E_p=\frac{C_I{L}_u}{C_u{L}_t-C_t{L}_u};$

Wherein, the pin capacitor C of receiving device _IManufacturer provides by receiving device.

As a preferred embodiment of the present invention, in order to allow the electric capacity of pin of receiving device more can Approximate Equivalent be evenly distributed on the thin transmission line, thin transmission line cloth is at the two ends of the pin pad of receiving device, the isometric (E of the length of the thin transmission line in two ends _p/ 2).

Fig. 6 shows the circuit theory of pcb board provided by the invention, and driver is A, and first, second and third receiving device is followed successively by B, C, D, and the node of the newly-increased thin transmission line of pcb board is respectively 1,2,3,4,5,6.Suppose the length Ep=10mil (mil of thin transmission line 1-2,1mil=0.0254mm), then the thin transmission line with receiving device pin two ends keeps isometric, be B-1=B-2=5mil, so that the electric capacity of the first receiving device pin more can Approximate Equivalent be evenly distributed on the thin transmission line 1-2, for more can being similar to, the electric capacity that makes second, third receiving device pin is evenly distributed on thin transmission line 3-4, the 5-6 accordingly, thin transmission line C-3 and C-4, D-5 and D-6 also satisfy above-mentioned relation respectively, repeat no more.

After by the newly-increased thin transmission line of pcb board impedance being adjusted, as shown in Figure 7, obvious disappearance is colluded in returning of the simulation waveform of receiving device.

Below to use the pcb board software for drawing, for example candence, power PCB or Protel etc. are elaborated for the wiring process of example to above-mentioned pcb board:

Suppose that network is called I28B_RDR1_DQB8, cabling from U20.A14 point (being A point Fig. 7) to U49.T7 point (being the B point among Fig. 7), length 1200-1250mil (mil, 1mil=0.0254mm) in the scope, wherein thin length of transmission line (being the B1 among Fig. 7) in the 460-480mil scope.

1. the thick transmission line create-rule that network I28B_RDR1_DQB8 is set in rule management is as shown in the table, clicks executive button, and software generates corresponding thick transmission line automatically, as shown in Figure 8.

U20.A14:U49.T7 in the last table is illustrated in and generates thick transmission line between U20.A14 and the U49.T7.Min be 1200 and Max be 1250 the expression require the track lengths of thick transmission line between 1200mil-1250mil.Actual represents on the pcb board length of the actual cabling of thick transmission line, and Margin represents the actual cabling surplus of thick transmission line, promptly is respectively the poor of the difference of Actual value and Min value and Max value and Actual value.

2. choose the network that need attenuate, can choose one or more networks, during elected majority network, software will extract each topology of networks, and relatively whether each topology of networks is consistent, if unanimity then proceed following operation, otherwise need reselect network.

3. the direction of the transmission line that attenuates as required, length, live width, manually (T point is to add an individual virtual point on certain section at network selecting, be provided with the T point on the network, to make things convenient for definition rule) be I28B_RDR1_DQB8.T.1, it is as shown in the table to increase corresponding rule simultaneously in rule management:

Click the corresponding button, software generates thin transmission line with corresponding cabling between U49 on the network and T point automatically, as shown in Figure 9.

Except the cabling of above-mentioned mode by selecting network with pcb board attenuates and can also attenuate by the cabling of receiving device name (or encapsulation) with some pcb board, the receiving device name is unique in the time of single board design, encapsulation is a kind of representation of receiving device profile on pcb board, and detailed process is as follows:

1. understand to need change the receiving device (or encapsulation) of live width, put the network on each receiving device in order, if do not need the network that attenuates then it is defined as power supply or zone network.

2. choose the receiving device (or encapsulation) that needs to change live width, in the rule management of software, increase the T point, generate corresponding rule, the minimum length Min that for example imports thin transmission line is 460mil, the maximum length Max of thin transmission line is 480mil, thin transmission line width W idth is 4mil etc., and is as shown in the table:

3. the network on the receiving device chosen of software analysis (or encapsulation) if power supply ground attribute is arranged on the network, does not then deal with, otherwise is the center with this receiving device (or encapsulation) pin, all generates long 460mil on its cabling both sides, the thin transmission line of wide 4mil.

The above only is preferred embodiment of the present invention, not in order to restriction the present invention, all any modifications of being done within the spirit and principles in the present invention, is equal to and replaces and improvement etc., all should be included within protection scope of the present invention.

Claims (4)

1, a kind of wiring method of printed circuit board (PCB), described printed circuit board (PCB) is provided with a plurality of receiving devices, connects by transmission line between the pin pad of described receiving device, it is characterized in that described method comprises:

Cloth one thin transmission line between the pin pad of described receiving device and described transmission line, the pin pad of the described receiving device of a termination of described thin transmission line, the described transmission line of another termination, wherein, the length of described thin transmission line is pressed following formula and is determined:

$E_p=\frac{C_I{L}_u}{C_u{L}_t-C_t{L}_u};$

Wherein, C _IBe the pin electric capacity of receiving device, L _uAnd C _uBe distributed inductance on the described transmission line and distributed capacitance, L _tAnd C _tBe distributed inductance and the distributed capacitance on the described thin transmission line.

2, the wiring method of printed circuit board (PCB) as claimed in claim 1 is characterized in that, at the two ends of the pin pad of described receiving device, wherein, the length of the thin transmission line at the pin pad two ends of described receiving device is isometric with described thin transmission line cloth.

3, a kind of printed circuit board (PCB), described printed circuit board (PCB) is provided with a plurality of receiving devices, connect by transmission line between the pin pad of described receiving device, it is characterized in that, be furnished with a thin transmission line between the pin pad of described receiving device and the described transmission line, the pin pad of the described receiving device of a termination of described thin transmission line, the described transmission line of another termination, wherein, the length of described thin transmission line is pressed following formula and is determined:

$E_p=\frac{C_I{L}_u}{C_u{L}_t-C_t{L}_u};$

Wherein, C _IBe the pin electric capacity of described receiving device, L _uAnd C _uBe distributed inductance on the described transmission line and distributed capacitance, L _tAnd C _tBe distributed inductance and the distributed capacitance on the described thin transmission line.

4, printed circuit board (PCB) as claimed in claim 3 is characterized in that, at the two ends of the pin pad of described receiving device, wherein, the length of the thin transmission line at the pin pad two ends of described receiving device is isometric with described thin transmission line cloth.

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