JP2904135B2 - Printed wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board used for a circuit configuration and a wiring member of an electronic device, and more particularly to an improvement of a printed wiring board intended for matching characteristic impedance of a transmission line.

[0002]

2. Description of the Related Art As the speed of an electronic circuit increases, the frequency of a signal to be transmitted also increases, and matching of the characteristic impedance of a transmission line becomes important. Here, if the characteristic impedance of the transmission line is matched, when transmitting a digital signal, it is effective to prevent erroneous recognition of a signal due to ringing or reflection, and to prevent electromagnetic wave interference. Also, when transmitting an analog signal, it is effective for transmitting a high-quality signal with suppressed waveform distortion, accentuation and attenuation.

Conventionally, methods for matching the characteristic impedance of a transmission line are roughly classified into a method performed at the stage of manufacturing a printed wiring board and a method performed after the printed wiring board is manufactured. The following various systems are known. In the following various systems, the first to third systems are performed at the stage of manufacturing a printed wiring board, and the fourth and fifth systems are performed after the printed wiring board is manufactured. The first method is a method of changing the conductor pattern width and thickness of the transmission line, for example, in a case where a rigid printed wiring board is connected by a flexible printed wiring board. By changing the thickness, the characteristic impedance of the transmission line is matched (for example, JP-A-7-106766). The second method is to adjust the thickness of the insulating layer according to the characteristics of the transmission line (for example, Japanese Patent Publication No. 7-5487).
No. 5). The third method is to select a material according to the characteristics of the transmission line and adjust the dielectric constant of the insulating layer (for example, Japanese Patent Publication No. 7-83185). The fourth method is to provide a plurality of ground wiring layer patterns and corresponding through holes, and selectively connect the through holes to match a characteristic impedance of a transmission line after manufacturing a multilayer printed wiring board. (For example, JP-A-6-252563). The fifth method is to insert a damping resistor or a terminating resistor into a signal line, which is generally known as a method of matching the characteristic impedance of a transmission line on a circuit.

[0004]

However, in the first method (the method of adjusting the width and thickness of the conductor pattern of the transmission line), if the characteristic impedance of the transmission line is increased, the width of the conductor pattern of the transmission line is reduced. Or the thickness must be reduced, so that the conductor pattern is easily cut or easily affected by the accuracy of the etching process. Not only is it easy to deviate from the intended characteristic impedance, but also the technical problem that the conduction resistance of the transmission line increases, and the transmission signal is unnecessarily attenuated. In the second method (the method of adjusting the thickness of the insulating layer), if the characteristic impedance of the transmission path is to be increased, the thickness of the insulating layer must be increased.
Difficult to apply to flexible printed wiring boards. Further, in the third method (the method of adjusting the dielectric constant of the insulating layer), it is necessary to select a material according to the characteristics of the transmission line. It is difficult to accurately match the characteristic impedances of the two. Furthermore, since these first to third methods are all intended to match the characteristic impedance at the stage of manufacturing the printed wiring board, it is not possible to adjust the characteristic impedance after manufacturing the printed wiring board. Can not.

In the fourth method (selective connection method for ground wiring layer), a plurality of ground wiring layers and a plurality of through holes are provided in advance for adjusting characteristic impedance, and the through holes are formed. Since selective connection is required, the space for the ground wiring layer and through hole for adjusting the characteristic impedance is indispensable, which not only increases the size of the printed wiring board but also increases the number of printed wiring board layers. However, there is a technical problem that it is difficult to apply it to a flexible printed wiring board as it is. Furthermore, among the fifth methods (damping resistance, terminating resistance insertion method), in the generally known damping resistance insertion method, the time constant on the circuit associated with the damping resistance is increased, so that it is reached. There are technical issues such as a decrease in signal potential and a decrease in transmission speed due to waveform distortion.On the other hand, in the case of a termination resistor insertion method,
Since the current consumption increases by the amount of insertion of the terminating resistor, the driving capability must be set high, and a situation arises in which the demand for lowering the power supply cost by increasing the power supply capacity is correspondingly raised.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problems, and it is an object of the present invention to easily and accurately match the characteristic impedance of a transmission line while reliably avoiding various disadvantages of the conventional system. It is intended to provide a printed wiring board capable of performing the following.

[0007]

Means for Solving the Problems That is, the present invention is, as shown in FIG. 1, the ground wiring in response to the signal wiring layer 1
In the printed wiring board on which the layer 2 is provided,
The wiring layer 2 includes a signal wiring layer 1 on a printed wiring board.
A first ground wiring layer 2a provided separately from
Connected to the first ground wiring layer 2a via the resistor 4.
The second ground wiring layer 2b is provided.
It is. In particular, representative embodiment of the present invention, as shown in FIG. 1, in the printed wiring board ground wiring layer 2 is provided corresponding to the signal wiring layer 1, the ground wiring layer 2, a printed wiring board And adjacent to the signal wiring layer 1
And a second ground wiring layer 2b provided with an insulating layer 3 interposed between the signal wiring layer 1 and the first ground wiring layer 2a and the second ground. A resistor 4 is interposed between the resistor 4 and the wiring layer 2b.

[0008]

In such technical means, the object of the present invention is to include all multilayer printed wiring boards,
Of course, it is preferable because it can be easily applied to a flexible printed wiring board requiring flexibility, as well as a hard printed wiring board. The method of manufacturing the printed wiring board is appropriately selected as long as the signal wiring layer 1 and the ground wiring layer 2 are formed using a substrate with a single-sided metal foil or a substrate with a double-sided metal foil and using a known etching process or the like. You can do it. The signal wiring layer 1 is formed by forming a signal wiring pattern with a conductor.
Is a wiring pattern connected to a reference potential formed of a conductor. It is obvious that the power supply layer may be used as a ground wiring layer if the power supply layer is set to a reference potential in addition to the ground, not to mention the grounded one. It may be.

Further, the characteristic impedance of the printed wiring board of the present invention is matched by adopting a microstrip structure or a strip structure. In this case, the wiring pattern of the signal wiring layer 1 and the wiring pattern of the second ground wiring layer 2b form a microstrip line or a strip line.

As the resistor 4, a resistor having a predetermined resistance value, a resistor component or a conductive paste printed material may be appropriately selected. Examples of the resistance component include a well-known resistance component with a lead made of carbon film or metal oxide, and a chip-type resistance component. Here, it is possible to easily obtain a desired resistance value by using an existing resistance component, and since the characteristic impedance is controlled by changing the resistance value, the desired characteristic impedance can be easily obtained. Can be In particular, mounting using a chip-type resistor component is preferable in that the interlayer connection and the insertion of the resistor can be performed at one time, and the device can be compactly mounted.

Further, if a conductive paste is used for the resistor 4, it is less expensive than a method of mounting a resistive component, and moreover, the interlayer is filled by filling the conductive paste in the buyer hole of the insulating layer 3. It is preferable in terms of space saving because it is connected. In particular, in the case of a type using a conductive paste, it is necessary to cover the conductive paste with a coverlay so that this portion does not accidentally come into contact with a conductor such as a frame.

The first ground wiring layer 2a and the second ground wiring layer 2b are usually formed on different surfaces with the insulating layer 3 interposed therebetween. This is preferable because it also serves as a means for making a connection and does not require a separate means for making an interlayer connection. On the other hand, when the first ground wiring layer 2a is formed over the opposite side surface of the insulating layer 3 via a conductive portion (such as through-hole plating) provided on the insulating layer 3, the first ground wiring layer 2a is formed. Since the second ground wiring layer 2b and the second ground wiring layer 2b are on the same plane, the resistor 4 may be interposed on the same plane at this time.

Next, the operation of the above technical means will be described. In the printed wiring board shown in FIG. 1, since the resistor 4 is interposed between the first ground wiring layer 2a and the second ground wiring layer 2b, the resistance value of the resistor 4 is adjusted. By doing so, the characteristic impedance of the transmission path is controlled.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. First Embodiment FIG. 2 shows a usage example of a first embodiment of a printed wiring board to which the present invention is applied. In the figure, a printed wiring board 20 to which the present invention is applied has flexibility and is used as a long wiring component for connecting between hard printed wiring boards 21 and 22. In the present embodiment, as shown in FIGS. 3 to 5, the printed wiring board 20 has a two-layer structure in which flexible single-sided printed boards 30 and 40 are stacked, and a single-sided one located on the lower side. The printed circuit board 30 has a signal wiring layer 3 on one surface (upper surface) of an insulating base 31 having a constant thickness.
2 and the first ground wiring layer 33 is formed on the outer side in the width direction of the signal wiring layer 32 region. On the other hand, the single-sided printed circuit board 40 located on the upper side has one side of the insulating base 41 having a constant thickness (FIG. The second ground wiring layer 42 is formed over substantially the entire area of the upper surface). In this embodiment, the wiring pattern of the signal wiring layer 32 and the wiring pattern of the second ground wiring layer 42 form a microstrip line.

In the present embodiment, the printed wiring board 2
As a method of manufacturing the signal wiring layer 32 and the first wiring, a known method such as etching is applied to a plate with a single-sided metal foil in which a metal foil (for example, a copper foil) is laminated on one side of the insulating bases 31 and 41, for example. By forming wiring patterns corresponding to the ground wiring layer 33 and the second ground wiring layer 42, single-sided printed boards 30 and 40 are formed, and a method of integrally stacking them while positioning them is adopted (for example, JP-A-6-334339).

Further, both ends in the longitudinal direction of the printed wiring board 20 according to the present embodiment have a shape in which the lower layer protrudes from the upper layer side, and the signal wiring layer 32 of the lower single-sided printed circuit board 30 and both sides thereof The ends of the first ground wiring layer 33 are configured as terminal portions 34 connected to the hard printed wiring boards 21 and 22, respectively. A chip-type resistor is provided between the first ground wiring layer 33 of the terminal portion 34 of the lower single-sided printed board 30 and the end of the second ground wiring layer 42 of the upper single-sided printed board 40. The component 50 is mounted and connected diagonally across the first and second ground wiring layers 33 and 42. Here, in the present embodiment, the resistance values of the chip-type resistor components 50 mounted on both ends of the printed wiring board are all set to the same value. Reference numeral 51 denotes solder for mounting the chip-type resistance component 50.

FIG. 6 schematically shows a transmission circuit (transmission path) according to the present embodiment. In the drawing, a second ground wiring layer 42 is connected to the first ground wiring layer 33 via a chip-type resistor component 50, and the first ground wiring layer 33 is grounded. Accordingly, the first ground wiring layer 33 functions as a normal ground line because it is arranged near the signal wiring layer 32 and does not pass through a resistor.

Next, the characteristic impedance of the transmission line of the printed wiring board according to the present embodiment is measured. The characteristic impedance measurement used in the present embodiment uses, for example, HP54120 manufactured by Hewlett-Packard Company, and uses TDR (Time Domain) using the response of a pulse signal.
(Reflectometry) method. At this time, the resistance values (20 Ω, 51 Ω in the present embodiment) of the chip-type resistance component 50 are changed, and the measurement results of the characteristic impedance are shown in FIG. In the figure, conduction means a state where both are short-circuited (resistance is zero), and non-connection means a state where both are insulated. In addition, in FIG. 7, when measuring the characteristic impedance, the width of the conductor of the signal wiring layer was appropriately changed, and the relationship between the two was also examined. According to FIG. 7, it is understood that the characteristic impedance is finely adjusted by appropriately changing the resistance value of the chip-type resistor component 50.

In this embodiment, the printed wiring board 2
0, two chip-type resistor components 50 are provided at both ends,
Although the respective resistance values are set to be the same, for example, the chip-type resistance parts 5 are provided one at each end of the printed wiring board 20.
0 may be provided, and even if two chip-type resistor components 50 are provided at both ends of the printed wiring board 20, respectively, the signal wiring layer 32 and the ground wiring layer 3 may be provided.
3 and 42, two chip-type resistor components 5
The resistance value of 0 may be changed to a different value.

Second Embodiment FIG. 8 shows a second embodiment of a printed wiring board to which the present invention is applied. In the figure, a printed wiring board 20 is a board with a double-sided metal foil in which metal foils are laminated on both sides of an insulating base 61, and is formed by a well-known through-hole plating and pattern formation by a subtractive method. 1. It was manufactured as a double-sided printed wiring board in which the second ground wiring layers 63 and 64 were laminated. In the present embodiment, the signal wiring layer 62 is provided on one surface (lower surface) of the insulating base 61.
Are formed, and a first ground wiring layer 63 is formed on both sides thereof, while a second ground wiring layer is formed on a portion of the insulating base 61 opposite to the signal wiring layer 62 on one other surface (upper surface). The first ground wiring layer 63 and the through-hole plating 6 are provided on both sides thereof.
A conductive layer 66 (corresponding to the first ground wiring layer 63) that conducts through the conductive layer 5 is laminated. The chip-type resistor component 50 is mounted and connected by the solder 51 on the same surface across the second ground wiring layer 64 and the conductive layer 66, and is grounded to the first ground wiring layer 63 and the second ground wiring layer 64. A chip-type resistance component 50 is interposed between the chip-type resistance component 50 and the ground wiring layer 64. In the figure, reference numeral 67 denotes a plating layer. Therefore,
In the present embodiment, as in the first embodiment, the characteristic impedance can be controlled by appropriately changing the resistance value of the chip-type resistor component 50.

Third Embodiment FIG. 9 shows a printed wiring board according to a third embodiment of the present invention. In the same figure, the printed wiring board 20 has a two-layer structure (single-sided two-layer FPC) in which flexible single-sided printed boards 30 and 40 are laminated, similarly to the first embodiment. The signal wiring layer 3 on the single-sided printed circuit board 30
2 and the first ground wiring layer 33, the second ground wiring layer 42 is formed on the upper single-sided printed circuit board 40, and the lower layer side of the longitudinal ends of the single-sided printed circuit boards 30, 40 is higher than the upper layer side. The terminal portion 34 (see FIG. 3) is projected. In the present embodiment, the connection structure of the first and second ground wiring layers 33 and 42 is different from that of the first embodiment in that a buyer hole is used to connect the first and second ground wiring layers 33 and 42. 71 was formed, and a carbon paste (Asahi Scientific Research Institute TU-30SKC) as the conductive paste 72 was filled therein. At this time, by using a carbon paste as the conductive material to be filled, the connection resistance of the buyer hole 71 was increased, and the same state as that in which a resistor was interposed between both layers was obtained. That is, it was confirmed that the characteristic impedance can be controlled by appropriately changing the resistance value of the conductive paste 72.
In the present embodiment, the surface of the printed wiring board is covered with a coverlay (not shown), and the situation where the conductive paste 72 contacts the outside is avoided.

[0023]

As described above, according to the present invention,
Since a resistor is interposed between the first ground wiring layer and the second ground wiring layer, and the resistance value of the resistor is adjusted, the characteristic impedance of the transmission line is controlled. Therefore, even after manufacturing the printed wiring board, the characteristic impedance can be easily and accurately adjusted, and the matching of the characteristic impedance of the transmission line can be reliably performed. Therefore, waveform distortion, noise, and erroneous recognition of signals due to impedance mismatching of digital signals and analog signals can be reduced, and signal transmission with good waveform quality can be reliably realized. Also, in the signal pattern of the microstrip structure and the strip structure,
It is possible to easily obtain a high characteristic impedance without reducing the width of the conductor pattern of the signal wiring layer or increasing the thickness of the insulating layer. For this reason, adverse effects (variation in characteristic impedance due to manufacturing errors due to cut-off or etching of the signal wiring layer) due to the signal wiring layer being too thin can be eliminated, and the insulating layer can be made as thin as necessary. Application to a flexible printed wiring board can be facilitated. Further, since it is not necessary to insert a damping resistor or a terminating resistor in the signal wiring layer, it is possible to reliably prevent various adverse effects such as a reduction in signal potential, a reduction in transmission speed, and an increase in power supply capacity.

Further, in the present invention, if the resistor also serves as the interlayer connection of the insulating layer, other means for making the interlayer connection becomes unnecessary, and the configuration of the printed wiring board is correspondingly simplified. can do.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an outline of a printed wiring board according to the present invention.

FIG. 2 is an explanatory diagram illustrating an example of use of the printed wiring board according to the first embodiment;

FIG. 3 is a detailed view of a portion III in FIG. 2 of the printed wiring board according to Embodiment 1;

FIG. 4 is a sectional view taken along line VI-VI in FIG. 3;

FIG. 5 is a sectional view taken along line VV in FIG. 3;

FIG. 6 is a schematic diagram showing a circuit configuration of the printed wiring board according to the first embodiment.

FIG. 7 is a graph showing a characteristic impedance change for each signal wiring layer conductor width when the resistance value of the chip-type resistance component is changed in the first embodiment.

FIG. 8 is an explanatory sectional view similar to FIG. 4, illustrating a printed wiring board according to a second embodiment;

FIG. 9 is an explanatory sectional view similar to FIG. 4, illustrating a printed wiring board according to a third embodiment;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... signal wiring layer, 2 ... ground wiring layer, 2a ... 1st ground wiring layer, 2b ... 2nd ground wiring layer, 3 ... insulating layer, 4 ... resistor, 20 ... printed wiring board, 31 ... insulating base 32, a signal wiring layer, 33, a first ground wiring layer, 41, an insulating base, 42, a second ground wiring layer,
Reference numeral 50: chip-type resistance component, 61: insulating base, 62: signal wiring layer, 63: first ground wiring layer, 64: second ground wiring layer, 65: through-hole plating, 66: conductive layer, 71: buyer Hole, 72 ... conductive paste

Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) H05K 1/02 H05K 3/46

Claims (8)

(57) [Claims] In a printed wiring board provided with a ground wiring layer (2) corresponding to a signal wiring layer (1), the ground wiring layer (2) is on the printed wiring board,
A first ground wiring layer (2a) provided adjacent to the signal wiring layer (1) , and a second ground wiring layer (2) provided with the insulating layer (3) interposed between the signal wiring layer (1).
b), wherein a resistor (4) is interposed between the first ground wiring layer (2a) and the second ground wiring layer (2b). 2. The printed wiring board according to claim 1, wherein the resistor (4) also serves as a means for making an interlayer connection between the insulating layers (3). 3. The printed wiring board according to claim 1, wherein the first ground wiring layer extends through a conductive portion provided on the insulating layer to an opposite side surface of the insulating layer. A printed wiring board formed, wherein a resistor (4) is interposed on the same surface as the second ground wiring layer (2b). 4. The printed wiring board according to claim 1, wherein the resistor (4) has a resistance component mounted thereon. 5. The printed wiring board according to claim 1, wherein the resistor is printed with a conductive paste. 6. The printed wiring board according to claim 1, wherein the wiring pattern of the signal wiring layer (1) and the wiring pattern of the second ground wiring layer (2b) form a microstrip line or a strip line. Printed wiring board featuring. 7. The printed wiring board according to claim 1, wherein the printed wiring board has flexibility. 8. A printed wiring board provided with a ground wiring layer (2) corresponding to the signal wiring layer (1), wherein the ground wiring layer (2) is on the printed wiring board,
A first ground wiring layer (2a) provided separately from the signal wiring layer (1); and a second ground wiring layer (2) connected to the first ground wiring layer (2a) via a resistor (4). 2b). A printed wiring board comprising: