JP6226739B2 - Printed wiring board - Google Patents

Description

  The present invention relates to a printed wiring board for differential transmission.

Signal transmission performed on a printed wiring board is roughly classified into single-ended transmission and differential transmission. As shown in FIG. 11 (a), differential transmission is composed of a set of two transmission lines, and positive (P: Positive) and negative (N: Negative) logic signals are simultaneously transmitted from signal 1 and signal 2, respectively. Output from the driver and input to the receiver. FIG. 11B shows the time change of the voltage amplitude of the signal 1 and the signal 2. The vertical axis represents voltage amplitude, and the horizontal axis represents time. The positive logic signal 1 has a Hi level signal of 1 and a Low level signal of 0. In the negative logic signal 2, the Hi level signal is 0 and the Low level signal is 1. Signal 1 and signal 2 are simultaneously output from the driver, and the receiver processes the two signals so as to obtain a difference at the same timing. A difference in voltage amplitude acquired by the receiver is represented by V _SIGNAL (P) −V _SIGNAL (N) shown in FIG. As shown in the figure, the receiver can obtain an amplitude twice as large as the individual voltage amplitude at the same rising speed. Therefore, the differential signal circuit has two output and input wirings for one signal, and the two signals are always at different levels of the Hi level and the Low level.

  In the case of a linear differential transmission line, even when receiving noise as shown in FIG. 11 (d), the line structures on the signal 1 side and the signal 2 side are substantially the same and the influence of noise is also substantially the same. Thus, the reading value of the voltage acquired as the difference is not affected (see FIG. 11E). Since there is a merit against noise as described above, the differential transmission method is widely adopted in many high-speed serial transmission standards.

  In recent years, differential transmission lines having a wide variety of wiring patterns have been provided, and a differential transmission line having a curved wiring path is often required as shown in FIG. As described above, when the logic signal changes, the Hi level signal changes simultaneously to the Low level signal, and the Low level signal changes simultaneously to the Hi level signal. If the wiring lengths of the two signal lines are the same, it is possible to transmit a signal from the driver to the receiver without timing deviation. However, in a transmission line with a bent portion as shown in FIG. 12A, the length of the signal line located on the outer circumference side of the bend is different from the length of the signal line located on the inner circumference side. It will be different. For this reason, as shown in FIG. 12B, a deviation occurs at the timing when the signal reaches the receiver. If a deviation occurs in the arrival timing of the signal, as shown in FIG. 12C, the voltage waveform obtained by the difference in the receiver may be collapsed and a reading error may occur.

  Therefore, in order to align the line lengths of the paired signal lines in the differential transmission line, as shown in FIG. 9 of Patent Document 1, zigzag meander wiring can be applied to the signal lines located on the inner peripheral side. Proposed. By applying the meander wiring, the signal lengths of the inner and outer signal lines of the bent portion are equalized, and therefore the signal propagation time from one end of these signal lines to the other is equal. For this reason, even when noise is mixed in the signal (input signal) output from the driver, the timing at which the noise reaches the receiver coincides. Therefore, this noise can be removed by acquiring the difference in voltage amplitude between the Hi level signal and the Low level signal with the receiver.

  However, since the meander wiring needs to prepare a region that protrudes in a zigzag manner in the width direction of the signal line, there is a problem that a large wiring space is required in the width direction of the signal line. In addition, the meander wiring causes signal reflection at the zigzag portion to generate new noise, and the characteristic impedance changes due to the gap between the signal lines changing at the zigzag portion, resulting in impedance mismatch. There is a problem.

  On the other hand, in Patent Document 1, the first and second dielectric layers are stacked so as to sandwich the wiring layer on which a plurality of signal lines are formed, and the signal line region with a shorter line length is the signal line. The effective dielectric constant of the second dielectric layer immediately above is increased (see Patent Document 1: FIG. 2). As a result, the wavelength shortening rate of a signal transmitted through a signal line having a short line length is increased and the delay time of the signal is increased, so that the propagation time of the signal transmitted through the differential signal line pair is equalized. .

  Further, Patent Document 2 describes a wiring board in which a large number of openings are formed in a pattern on a ground layer facing a wiring layer on which a plurality of signal lines are formed. By increasing the aperture ratio of the opening pattern in the area where the signal line with a short line length is formed, the transmission speed of the signal passing through the signal line decreases, so the signal delay in multiple signal lines with different line lengths It is assumed that time (propagation time) becomes equal.

JP 2005-175078 A JP 2000-77802 A

  However, in the invention of Patent Document 1, since the second dielectric layer needs to be formed above the wiring layer, there is a problem that the thickness dimension of the printed wiring board is increased. The first dielectric layer sandwiched between the ground conductor and the signal line greatly contributes to increasing the signal wavelength reduction rate, but the second dielectric layer formed on the opposite side of the ground conductor from the signal line. The dielectric layer has very little effect of increasing the wavelength shortening rate of the signal. For this reason, in the case of a wiring pattern having a large difference in signal line length, the delay time in the paired signal lines cannot be made sufficiently equal by the method of Patent Document 1.

  In the invention of Patent Document 2, it is possible to equalize the signal delay time between a plurality of pairs of differential wirings, but the signal propagation times in a pair of differential wirings cannot be made equal to each other. This is because the scale of the opening formed in the ground layer is much larger than the wiring interval of the differential wiring pair, so that the line structures of the differential wiring pair are substantially equal. For this reason, it is not possible to eliminate the deviation in the arrival timing of the signals due to the difference in the line length between the signal lines on the inner peripheral side and the outer peripheral side. In the invention of Patent Document 2, a large number of openings are formed in the ground layer, so that the shielding effect by the ground layer is lowered. Furthermore, the ground layer has a function of a conductor layer through which a return signal of the signal transmitted through the signal line flows. However, since the opening is formed in the ground layer, the return signal transmission path becomes complicated. The path length of the return signal varies. For this reason, it becomes difficult to control the transmission rate of the return signal.

  The present invention has been made in view of the problems as described above, and suppresses the occurrence of deviation in signal arrival timing even when the signal line for differential transmission is formed with a curved or bent wiring pattern. A printed wiring board capable of stable signal transmission is provided.

According to the present invention, at least a pair of signal lines for differential transmission formed in parallel, a conductor layer provided opposite to the signal line, and the signal layer and the conductor layer are sandwiched. An insulating resin layer, and the pair of signal lines have a bent portion that is bent or bent in a plane of the signal layer, and the first signal line located on the outer peripheral side of the bent portion; The second signal line, which is located on the inner peripheral side of the bent portion and has a line length shorter than that of the first signal line, and the insulating resin layer is located at a position facing the first signal line. A low dielectric region having a dielectric constant lower than that of the insulating resin layer is provided, and the low dielectric region is a void provided in the insulating resin layer and includes a vent hole communicating with the outside. A wiring board is provided.

  According to the printed wiring board of the present invention, the low dielectric region is provided at a position facing the first signal line located on the outer peripheral side of the bent portion. Here, since the signal propagation speed has a negative correlation with the relative dielectric constant of the insulating resin layer sandwiched between the signal layer and the conductor layer, the propagation speed in the first signal line facing the low dielectric region is improved. Therefore, the signal propagation time can be equalized between the second signal line on the inner circumference side and the first signal line on the outer circumference side, and the signal line for differential transmission is formed with a curved or bent wiring pattern. Even in this case, it is possible to prevent the signal arrival timing from being shifted. For this reason, according to the printed wiring board of the present invention, stable signal transmission is possible.

It is a top view of the printed wiring board concerning the first embodiment of the present invention. (A) is an enlarged view of the area | region X shown in FIG. FIG. 2B is an enlarged view of a region Y shown in FIG. It is the sectional view on the AA line shown to Fig.2 (a). FIG. 3 is a sectional view taken along line BB shown in FIG. It is CC sectional view taken on the line shown to Fig.2 (a). It is the DD sectional view taken on the line shown in FIG.2 (b). It is sectional drawing which shows the modification of the printed wiring board of 1st embodiment. It is an enlarged plan view of the signal line of the first embodiment. (A) to (f) is a cross-sectional view showing the method for manufacturing a printed wiring board of the first embodiment. (A) to (f) is a cross-sectional view showing a method for manufacturing a printed wiring board according to a second embodiment of the present invention. (A)-(e) is a figure explaining the principle of differential transmission. (A) is a conceptual diagram of a differential transmission line, (b) is a graph showing temporal changes in voltage amplitude of positive and negative logic signals, (c) is a graph showing a difference in voltage amplitude of (b), (d) is The graph which shows the time change of the voltage amplitude of the logic signal containing a noise, (e) is a graph which shows the difference of the voltage amplitude of (d). (A) is a conceptual diagram of a differential transmission line having a bent portion, (b) is a graph showing a temporal change in voltage amplitude of a positive and negative logic signal, (c) is a graph showing a difference in voltage amplitude of (b). is there.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same constituent elements are denoted by the same reference numerals, and redundant description is omitted as appropriate. In the following description, there are cases in which the stacking direction is referred to as the vertical direction, but this is to explain the relative positional relationship between the layers, and the direction in which the printed wiring board 100 according to this embodiment is manufactured or used. It is not intended to limit.

<First embodiment>
A printed wiring board 100 according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a plan view of the printed wiring board 100. A region X shown in FIG. 1 is a straight portion 26, and a region Y is a bent portion 28. 2A is an enlarged view of the region X, and FIG. 2B is an enlarged view of the region Y. 3 to 5 are cross-sectional views taken along lines AA, BB, and CC shown in FIG. 2A, respectively. 6 is a cross-sectional view taken along the line DD shown in FIG. Note that the cross-sectional view taken along the line EE shown in FIG. 2B is the same as the cross-sectional view taken along the line CC in FIG.

  First, an outline of the present embodiment will be described. The printed wiring board 100 of this embodiment includes a signal layer 25, a conductor layer (ground layer 70), and an insulating resin layer 60. In the signal layer 25, at least a pair of parallel differential transmission signal lines 20 (a first signal line 21 and a second signal line 22) are formed. The conductor layer (ground layer 70) is provided to face the signal lines (first signal line 21 and second signal line 22). The insulating resin layer 60 is sandwiched between the signal layer 25 and the conductor layer (ground layer 70). The pair of signal lines 20 includes a bent portion 28 that is bent or bent in the plane of the signal layer 25, a first signal line (first signal line 21) located on the outer peripheral side of the bent portion 28, and a bent portion. 28, and a second signal line (second signal line 22) that is located on the inner peripheral side of the 28 and has a line length shorter than that of the first signal line 21. The insulating resin layer 60 of the printed wiring board 100 of the present embodiment is provided with a low dielectric region 40 having a dielectric constant lower than that of the insulating resin layer 60 at a position facing the first signal line 21. And

Next, this embodiment will be described in detail.
The printed wiring board 100 of the present embodiment is used in, for example, a portable electronic device, and the line length of each signal line 20 is several tens mm to several hundred mm. The printed wiring board 100 has a sheet shape. In the present specification, a film and a sheet are not distinguished.

  The printed wiring board 100 is provided with a signal layer 25 covered with a protective layer 80 (see FIG. 3) not shown in FIG. The printed wiring board 100 includes an insulating resin layer 60 as an inner layer. In FIG. 1, a part of the insulating resin layer 60 is viewed from the signal layer 25 located below the protective layer 80 (not shown). The signal layer 25 is a conductor layer that includes the signal line 20. In the vicinity of both ends of the signal line 20, ground pads 30 are arranged on both outer sides in the width direction. As shown in FIG. 3, the ground pad 30 and the signal layer 25 are in the same layer.

  The printed wiring board 100 of the present embodiment has one or more signal layers 25. Although FIG. 1 illustrates only the signal layer 25 including the pair of first signal lines 21 and second signal lines 22, a plurality of pairs of differential transmission lines may be included. The number of the signal lines 20 is arbitrary, and the signal layer 25 may optionally include a single-ended transmission line in addition to the differential transmission line. A printed wiring board 100 shown in FIG. 1 has a ground layer 70 that is a conductor layer on a surface opposite to the first signal line 21 and the second signal line 22 for differential transmission in a pair of two so-called micro-circuits. This is a differential transmission line having a stripline structure. The first signal line 21 and the second signal line 22 are differential transmission lines that are parallel to each other over substantially the entire length, and both are collectively referred to as a signal line 20.

  The signal line 20 includes the bent portion 28, and the specific shape and dimensions are not particularly limited. As an example, the signal line 20 of the present embodiment has a rounded U shape, has a plurality of bent portions 28 (28a, 28b), and has straight portions 26 between and at both ends.

  The straight portion 26 is a portion formed substantially straight and may be slightly curved. The bent portion 28 is a portion that is curved or bent in the plane of the signal layer 25 with a smaller radius of curvature than the straight portion 26. The bent portion 28 may be curved in a smooth solitary manner, or may be bent so as to be bent. Hereinafter, except for an explicit case, a curve and a bend are not distinguished and are collectively referred to as a curve. The shape of the printed wiring board 100 (insulating resin layer 60) in plan view is arbitrary, but in the present embodiment, the printed wiring board 100 (insulating resin layer 60) has a curved strip shape extending along the signal line 20. Further, unless explicitly indicated, the straight line portion / bending portion of the signal line 20 and the straight line portion / bending portion of the printed wiring board 100 (insulating resin layer 60) are not distinguished, and the straight line portion 26 / bending portion 28 Call it.

  As shown in FIG. 1, the pair of signal lines 20 (the first signal line 21 and the second signal line 22) have a plurality of bent portions 28a and 28b that are bent or bent in the same direction. The low dielectric region 40 is provided to face the first signal line 21 for each of the plurality of bent portions 28a and 28b. That is, since the bending directions of the plurality of bent portions 28a and 28b are the same, the difference in line length between the first signal line 21 and the second signal line 22 in each bent portion 28a and 28b is added. The signal delay time in the dynamic wiring pair becomes remarkable. On the other hand, in this embodiment, by providing the low dielectric region 40 for each of the bent portions 28a and 28b, signal delay in the first signal line 21 on the outer peripheral side is suppressed.

  The radius of curvature and the central angle of the bent portion 28 are not particularly limited, and the radius of curvature and the central angle of the plurality of bent portions 28a and 28b may be the same or different from each other. In the present embodiment, the radius of curvature R and the central angle (90 degrees) of the bent portions 28a and 28b are common. The curvature radius R is one order (10 times) or more larger than the line width of the signal line 20 (the first signal line 21 and the second signal line 22).

  As shown in FIG. 2A, in the straight portion 26 formed at the end portion of the printed wiring board 100, the insulating resin layer 60 is composed of a low dielectric region 40 and an insulating resin portion 45, and is viewed in plan view. In addition, a low dielectric region 40 is provided at a position overlapping the signal line 20. The low dielectric regions 40 and the insulating resin portions 45 are arranged alternately and regularly along the extending direction of the printed wiring board 100.

  The low dielectric region 40 of the present embodiment is a void provided in the insulating resin layer 60. However, as in the second embodiment described later, the low dielectric region 40 may be filled with another resin material having a dielectric constant lower than that of the insulating resin portion 45.

  In the bent portion 28 shown in FIG. 2B, a low dielectric region 40 is provided to face the first signal line (first signal line 21) which is a signal line on the outer peripheral side. The low dielectric region 40 in the bent portion 28 does not face the second signal line (second signal line 22) but faces only the first signal line 21.

  Thereby, the propagation speeds of the first signal line 21 and the second signal line 22 in the bent portion 28 are equalized. The reason will be described below.

The propagation speed τ of the signal transmitted through the signal line 20 is expressed by the following equation (2).
τ = C ₀ / √ε (2)
Where τ is the signal propagation speed, C ₀ is the speed of light, and ε is the effective relative dielectric constant of the insulating layer 10 (see FIG. 3) sandwiched between the signal layer 25 and the ground layer 70. As will be described later, the effective relative dielectric constant ε is obtained as ε ₁ and ε ₂ in the insulating resin portion 45 and the low dielectric region 40, respectively.

  From the above equation (2), it can be seen that the propagation speed τ decreases as the effective relative permittivity ε of the insulating layer 10 increases, and conversely, the propagation speed τ increases as the effective relative permittivity ε decreases. In the printed wiring board 100 of the present embodiment, a signal passing through the bending portion 28 is provided by providing the low dielectric region 40 at a position facing the first signal line 21 that is located on the outer peripheral side of the bending portion 28 and has a long line length. Can be made faster than the second signal line 22. For this reason, since the signal propagation time is equalized between the signal passing through the second signal line 22 having a short line length and the signal passing through the first signal line 21 having a long line length, there is a deviation in the arrival timing of the signal. Occurrence is suppressed.

  The signal propagation time T is the time until a signal passes from one end 21a, 22a to the other end 21b, 22b of the first signal line (first signal line 21) or the second signal line (second signal line 22). It is. The signal propagation time T can be expressed by the following formula (3) obtained by modifying the formula (2). In the printed wiring board 100 of the present embodiment, the signal propagation times T of the first signal line 21 and the second signal line 22 are equal to each other.

T = (L ₁ · √ (ε ₁ ) + L ₂ · √ (ε ₂ )) / C ₀ (3)
Where T is the signal propagation time of the first signal line (first signal line 21) or the second signal line (second signal line 22). L ₁ is opposed of the line length of the first signal line (first signal line 21) or the second signal line (second signal line 22), the insulating resin layer 60 (insulating resin portion 45) Length. L ₂ is a length of the first signal line (first signal line 21) or the second signal line (second signal line 22) facing the low dielectric region 40 among the line lengths. More specifically, the length L _{21 of} the first signal line 21 facing the low dielectric region 40 may be represented, and the length L _{22 of} the second signal line 22 facing the low dielectric region 40 may be represented. is there. ε ₁ is an effective relative dielectric constant of the formation region of the insulating resin layer 60 (insulating resin portion 45). ε ₂ is an effective relative dielectric constant of the formation region of the low dielectric region 40. C ₀ is the speed of light.

ε ₁ and ε ₂ are effective relative dielectric constants of the insulating layer 10 (see FIG. 3) sandwiched between the signal layer 25 and the ground layer 70. The insulating layer 10 is a general term for a stack including the insulating resin layer 60. In the present embodiment, the weighted average obtained by multiplying the individual relative dielectric constants of the insulating resin layer 60 (the insulating resin portion 45 or the low dielectric region 40), the adhesive layers 111 and 121, and the insulating base materials 112 and 122 by the thickness ratio of each layer. ε ₁ and ε ₂ can be determined.

In the straight line portion 26, the line lengths of the first signal line 21 and the second signal line 22 are equal to each other. Therefore, the length L ₂₁ that faces the low dielectric region 40 of the first signal line 21 when the insulating resin layer 60 or not provided a low dielectric region 40, or provided, the low of the second signal line 22 The length L ₂₂ facing the dielectric region 40 is preferably equal. Thereby, in the linear part 26, the propagation speed of the signal in the 1st signal line 21 and the 2nd signal line 22 becomes equal. In the bent portion 28, the low dielectric region 40 is provided so as to substantially face only the first signal line 21 as described above, and the propagation speed of the first signal line 21 is increased. In FIG. 5, the first signal line 21 and the second signal line 22 have the same signal propagation speed.

That is, the length L ₂₁ of the first signal line (first signal line 21) facing the low dielectric region 40 is equal to the low dielectric region 40 of the second signal line (second signal line 22). It is larger than the length L ₂₂ facing each other. As a result, at any position from the one end 21a, 22a of the signal line 20 to the other end 21b, 22b, the positive and negative logic signals are transmitted through the differential wiring pair without time delay. For this reason, even if a noise signal is mixed from the outside into an unspecified position of the signal line 20, the noise signal reaches the receiver at the same time. Therefore, the noise signal can be removed by acquiring the voltage amplitude difference with the receiver. In the case of a conventional printed wiring board provided with meander wiring, it is possible to adjust so that a time delay is eliminated by passing positive and negative logic signals through zigzag meander wiring. It cannot be removed. This is because when a noise signal is simultaneously mixed into the wiring pair from the outside in the line region up to the meander wiring, a time delay occurs in the noise signal by passing through the meander wiring. For this reason, the conventional printed wiring board has a problem that even if the noise signal mixed in the signal output from the driver can be removed, the electromagnetic wave noise mixed from the outside into the signal line 20 cannot be removed. On the other hand, according to the printed wiring board 100 of the present embodiment, not only the noise mixed in the signal output from the driver, but also the electromagnetic noise mixed in an unspecified position from the outside as described above is removed. Is possible.

  Hereinafter, the structure of the printed wiring board 100 of the present embodiment will be described in more detail.

  The low dielectric region 40 is provided in both the position facing the bent portion 28 and the position facing the linear portion 26 in the first signal line (first signal line 21). The low dielectric region 40 also faces the straight portion 26 of the second signal line 22.

  As a result, the dielectric constant of the insulating resin layer 60 is reduced as a whole with respect to the signal line 20 (the first signal line 21 and the second signal line 22), so that the signal propagation time T is shortened, in other words, the signal high speed. Transmission is possible.

  As shown in FIG. 2A, the low dielectric region 40 in the linear portion 26 is formed across the width direction of the signal line 20. The low dielectric region 40 of the present embodiment has a rectangular shape in plan view, but the shape and dimensions are arbitrary. The low dielectric region 40 may be formed in the full width dimension of the printed wiring board 100 or may be formed in a part of the width dimension of the printed wiring board 100.

  In the printed wiring board 100 of the present embodiment, straight portions 26 are provided between the bent portions 28a and 28b and at a plurality of locations (three locations) on both ends. The low dielectric region 40 may be formed in all the straight portions 26, or may be formed only in some of the straight portions 26 among the plurality of locations.

On the other hand, as shown in FIG. 2B, the planar view shape of the low dielectric region 40 provided at the position facing the bent portion 28 of the first signal line (first signal line 21) is that of the bent portion 28. It has a tapered shape that becomes wider toward the outer peripheral side. Specifically, it can be a sector or a triangle. By making the low dielectric region 40 wider toward the outer peripheral side of the bent portion 28, the effective relative permittivity ε ₂ of the region where the low dielectric region 40 is formed is suitably reduced, and the _second dielectric constant expressed by the above equation (2) is obtained. The propagation speed τ of one signal line 21 can be increased.

  The low dielectric region 40 of the present embodiment is a void formed in the insulating resin layer 60 and has a vent hole communicating with the outside of the printed wiring board 100. Accordingly, it is possible to prevent the printed wiring board 100 from being swollen or deformed due to heating in a process of mounting an electronic component on the printed wiring board 100 or a change in atmospheric pressure during transportation of the printed wiring board 100 or the like.

  The low dielectric regions 40 are discretely arranged at a plurality of locations along the extending direction of the signal line 20. The individual low dielectric regions 40 are not in communication with each other and are individually provided with openings 50.

  The insulating resin portion 45 that partitions the low dielectric region 40 exists in the thickness direction of the insulating resin layer 60. The thickness dimension of the insulating resin layer 60 can be kept constant by the insulating resin portion 45. That is, the insulating resin portion 45 can also function as a spacer in the thickness direction of the insulating resin layer 60. As an example, the width dimension (vertical dimension in FIG. 2A) of the low dielectric region 40 can be set to 0.1 mm or more and 10 mm or less. Moreover, the width dimension (same vertical dimension) of the insulating resin part 45 can be 1 mm or more and 10 mm or less. The insulating resin layer 60 ensures the rigidity in the thickness direction of the printed wiring board 100. Further, the printed wiring board 100 may be bent when incorporated in the device, or may be subjected to an external force in the thickness direction during the manufacturing process. Even in such a case, the presence of the insulating resin layer 60 prevents the printed wiring board 100 from being crushed or the thickness of the low dielectric region 40 from changing.

  The low dielectric region 40 can be communicated with the outside of the printed wiring board 100 by having an opening 50 as shown in FIG. The opening 50 is preferably provided at a position different from that of the signal line 20, so that the presence of the opening 50 can prevent the transmission state of the signal line 20 from being disturbed. Specifically, as shown in FIG. 4, the opening 50 can be formed on the side end face in the thickness direction of the insulating resin layer 60. In addition to this, the area of the opening 50 is made sufficiently small to form an opening on the surface of the protective layer 80 (upper surface in FIG. 4), and the vent communicates with the low dielectric region 40 through the insulating base 112 and the protective layer 80. A hole may be provided. As a modification of the present embodiment, instead of providing the opening 50, any one of a top surface, a bottom surface, or a side surface surrounding the low dielectric region 40 is used as a gas permeable member, thereby making the low dielectric region 40 a printed wiring board. The outside of 100 may be communicated.

  By forming the opening 50 on the side end surface of the insulating resin layer 60 as in the present embodiment, when other electronic members are mounted on the front surface or the back surface of the printed wiring board 100, the selection of mounting locations can be narrowed. Absent. Further, as will be described later, an opening 50 can be provided at the outer edge of the printed wiring board 100 by simultaneously cutting the end portion of the low dielectric region 40 in the outer shape processing for cutting unnecessary portions around the outer edge at a later stage of the manufacturing process. .

An outline of the laminated configuration of the printed wiring board 100 will be described.
As shown in FIGS. 3 to 6, in the printed wiring board 100, the insulating base 112 having the signal line 20 and the insulating resin layer 60 (insulating resin portion 45) are bonded together by the adhesive layer 111. On the opposite surface of the insulating resin layer 60, an insulating base material 122 including a copper foil layer 123 is pasted by an adhesive layer 121. The ground layer 70 is constituted by the copper foil layer 123 and the plating layer 114 provided on the surface (lower surface). The printed wiring board 100 of the present embodiment has a so-called microstrip line structure in which the signal line 20 faces the ground layer 70 with the insulating resin layer 60 interposed therebetween.

  As shown in FIG. 3, the layer structure of the printed wiring board 100 includes a protective layer 80, a conductor layer (signal layer 25), an insulating base 112, an adhesive layer 111, and an insulating resin from the signal surface (signal line 20) side. A layer 60 (insulating resin portion 45), an adhesive layer 121, an insulating base 122, a conductor layer (ground layer 70), and a protective layer 80 are laminated. That is, the printed wiring board 100 has a symmetrical structure with the insulating resin layer 60 as the center.

  FIG. 4 shows a cross-sectional structure including the low dielectric region 40. Unlike FIG. 3, there are no adhesive layers 111 and 121 in addition to the insulating resin portion 45, and this portion becomes the low dielectric region (void portion) 40. The low dielectric region 40 can be formed by temporarily attaching the adhesive layers 111 and 121 to the insulating resin portion 45 in advance and punching them together with a mold or the like. As a result, both the dielectric constant and the dielectric loss tangent are reduced compared to the structure in which the insulating resin layer 60 is filled with the adhesive layers 111 and 121 and the insulating resin portion 45, the signal propagation speed τ is improved, and the transmission loss can be reduced. .

  FIG. 5 is a cross-sectional view showing a laminated structure of a portion of the transmission line that is not the low dielectric region (gap) 40, and has the same material configuration as the end cross-section of the printed wiring board 100 shown in FIG.

  FIG. 6 is a cross-sectional view showing a laminated structure of the bent portion 28 of the transmission line. A low dielectric region (gap portion) 40 is disposed only in a region facing the first signal line 21 located on the outer peripheral side of the bent portion 28, and an insulating resin portion 45 is disposed in a region facing the second signal line 22. Yes.

  Returning to FIG. 3, the signal layer 25 of the printed wiring board 100 is provided with a ground pad 30 in the same layer. In the first signal line 21 and the second signal line 22 constituting the signal line 20, a copper foil layer 116 and a plating layer 117 are laminated in this order on the upper surface of the insulating base 112. Similarly, in the ground pad 30, a copper foil layer 115 and a plating layer 114 are laminated in this order on the upper surface of the insulating base 112. The signal line 20 and the ground pad 30 may be formed separately, or may be simultaneously formed in the same process by patterning a copper foil formed on the insulating base 112 in a predetermined pattern. The ground pad 30 is a conductor portion wider than the signal line 20. The ground pad 30 is electrically connected through a through hole 90 to a ground layer 70 provided on the side surface opposite to the signal layer 25. The copper foil constituting the ground layer 70 and the signal line 20 is an example of a conductive member, and a conductive material other than the copper foil can be appropriately selected and used.

  The through hole 90 penetrates through the insulating resin portion 45 and connects the plating layer 114 in the ground pad 30 and the ground layer 70 to be electrically connected. An insulating resin portion 45 is provided around the through hole 90 in the insulating resin layer 60. The presence of the insulating resin portion 45 at and around the formation position of the through hole 90 allows the through hole 90 to be stably formed. The through hole 90 is not limited to that provided at the end of the printed wiring board 100 as shown in FIG. 1, and can be provided through the insulating resin layer 60 at an arbitrary location.

Each layer constituting the printed wiring board 100 will be described in detail.
As shown in FIGS. 3 to 7, a protective layer 80 is provided on the uppermost layer and the lowermost layer of the printed wiring board 100. The protective layer 80 can be made of an insulating material such as an insulating resin.

  Inside the protective layer 80, a signal layer 25 including the signal line 20 is provided. The signal line 20 (the first signal line 21 and the second signal line 22) is composed of a lower copper foil layer 116 and a plating layer 117 laminated thereon. The line width of the signal line 20 is designed to satisfy a predetermined specific impedance. The line width of the signal line 20 is not particularly limited, but can be created in a wide range, for example, 50 μm or more and 900 μm or less. The printed wiring board 100 according to the present embodiment is provided with a low dielectric region 40 in the insulating resin layer 60 to suppress the effective dielectric constant, thereby maintaining a desired characteristic impedance and 200 μm or more and 900 μm or less, and further 400 μm. A design having a relatively large line width of 800 μm or less can be realized.

  The line widths of the pair of signal lines 20 (first signal line 21 and second signal line 22) may be the same or different. Similarly, when a plurality of pairs of signal lines 20 are provided, the line width of each wiring pair may be common or different. Further, the line width of one signal line 20 (the first signal line 21 and the second signal line 22) may be constant over the entire length of the line length, or the line width is different at an arbitrary position as will be described later. It is also possible (see FIG. 8).

  The copper foil layer 116 can be patterned by printing, photolithography, or the like. The copper foil used for the copper foil layer 116 is an example of a conductive material. In addition to the copper foil, a conductive metal material such as a copper-containing composition or a silver-containing composition, or a metal foil such as a silver foil or a nickel foil can also be used. As the metal foil, a single-layer foil made of a single metal material may be used, or a thin foil made of a plurality of metal materials may be laminated.

  The plating layer 117 constituting the signal line 20 can be made of the same or different conductive material as the plating layer 114 that electrically connects the ground pad 30 and the ground layer 70 through the through hole 90. Examples of the material constituting the plating layer 114 and / or the plating layer 117 include electrolytic copper plating. Instead of the plating layer 114 and / or the plating layer 117, a conductive paste may be applied to the surfaces of the copper foil layer 116 and the copper foil layer 123.

  A conductor layer (ground layer 70) is provided on the opposite side of the signal layer 25 with the insulating resin layer 60 interposed therebetween. The ground layer 70 is formed by stacking a copper foil layer 123 and a plating layer 114. The conductor layer is a layer made of a conductive material, and includes a ground layer 70 and conductive layers such as a shield layer and a power supply layer. The conductor layer can be formed by the same material and method as the signal layer 25.

  An insulating base 112 is provided inside the signal layer 25, and the insulating base 112 is bonded to the upper surface of the insulating resin layer 60 by an adhesive layer 111. An insulating base 122 is provided inside the ground layer 70, and the insulating base 122 is bonded to the lower surface of the insulating resin layer 60 by an adhesive layer 121. The insulating base materials 112 and 122 can be made of glass epoxy, Teflon glass, alumina, or the like. The insulating base materials 112 and 122 may be made of the same material or different materials. By selecting a highly flexible material for the insulating bases 112 and 122, the printed wiring board 100 can be provided with flexibility, and a so-called flexible printed wiring board can be obtained. Examples of highly flexible materials include polyamide resins such as polyimide resins, polyamide resins, and polyamideimide resins; thermosetting resins such as epoxy resins; and thermoplastic resins such as liquid crystal polymers. In addition, an insulating fiber base material such as a glass woven fabric can also be used. In particular, from the viewpoint of reducing signal transmission loss, a polyimide resin or a liquid crystal polymer can be selected as a dielectric having a low dielectric constant. More specifically, for example, an insulating film mainly composed of a liquid crystal polymer and having a thickness of about 20 μm to 30 μm can be used as the insulating base materials 112 and 122 and combined with the insulating resin layer 60. As a result, it is possible to provide the printed wiring board 100 exhibiting flexibility in which transmission loss is significantly reduced.

  For the adhesive layers 111 and 121, the same kind or different kinds of insulating adhesive materials can be selected. For example, acrylic resin, epoxy resin, polyimide resin, liquid crystal polymer, glass epoxy, or the like can be used. The adhesive layers 111 and 121 can be formed by applying these adhesives by a printing method or by attaching an adhesive formed into a film shape. Specifically, for example, the adhesive layer 111 can be composed of a low-flow type bonding sheet having a glass epoxy resin, a polyimide resin, or a polyethylene terephthalate resin as a main component of the adhesive. The thickness of the adhesive layer 111 is not particularly limited, but may be, for example, about 10 μm to 20 μm.

  The insulating resin layer 60 includes the low dielectric region 40 and the insulating resin portion 45 as described above, and the low dielectric region 40 of the present embodiment is a gap. The low dielectric region 40 has an opening 50 on one or both of the long sides in a plan view of the printed wiring board 100. The insulating resin portion 45 can be made of the same material as the insulating base materials 112 and 122 described above. From the viewpoint of reducing transmission loss, the insulating resin portion 45 is preferably composed of polyimide resin or liquid crystal polymer. The insulating resin portion 45 may be made of a different material from the insulating base materials 112 and 122.

  The low dielectric region 40 may be provided over the entire thickness of the insulating resin layer 60, or may be provided only in a partial thickness of the insulating resin layer 60. In other words, the low dielectric region 40 may be provided so as to penetrate the insulating resin layer 60 in the thickness direction, or the surface of the insulating resin layer 60 (insulating resin portion 45) or a part of the inside thereof is formed in a concave shape. Thus, the low dielectric region 40 may be formed.

  The insulating layer 10 is a general term for an insulating laminate sandwiched between the signal layer 25 and the ground layer 70. Here, the distance from the insulating resin layer 60 to the signal layer 25 is referred to as “distance I”, and the distance from the insulating resin layer 60 to the ground layer 70 is referred to as “distance II”. When the distance I and the distance II are substantially equal, the capacitance between the signal line 20 and the ground layer 70 can be made smaller than when the distance I and the distance II are different. Further, when the distance I is smaller than the distance II, the effective non-dielectric constant can be made smaller than when the distance I and the distance II are substantially equal or when the distance II is larger than the distance I. In order to make the distance I smaller than the distance II, for example, the insulating base 112 may be omitted from the printed wiring board 100, or the layer thickness of the insulating base 112 may be made smaller than the layer thickness of the insulating base 122.

  FIG. 7 is a cross-sectional view showing a modified example of the printed wiring board 100 of the first embodiment, and corresponds to FIG. In 1st embodiment, as shown in FIG. 4, the insulating layer 10 is comprised only by the insulating base materials 112 * 122, and the insulating resin part 45 and the contact bonding layers 111 * 121 (refer FIG. 5) are not provided. On the other hand, in the insulating layer 10 of the modified example, only the insulating resin portion 45 is removed to form a low dielectric region (gap portion) 40, and the adhesive layers 111 and 121 are provided on the inner surfaces of the insulating base materials 112 and 122, respectively. . This is a structure created when the adhesive layers 111 and 121 are temporarily attached to the insulating resin portion 45 in the manufacturing method described later. According to this modification, the effective dielectric constant of the insulating layer 10 can be further reduced, which can contribute to a reduction in transmission loss.

  Although the printed wiring board 100 of this embodiment employs a microstrip line structure, the present invention can also be applied to a printed wiring board having a strip line structure. The present invention can also be applied to a wiring board in which the layer structure in which the signal layer 25 and the conductor layer (the ground layer 70) face each other with the insulating resin layer 60 interposed therebetween is composite or multilayered.

FIG. 8 is an enlarged plan view of the signal line 20 of the present embodiment. The line width of the first signal line (first signal line 21) continuously increases from a region facing the insulating resin layer 60 (insulating resin portion 45) to a region facing the low dielectric region 40. Yes. That is, the printed wiring board 100 is configured such that the width dimension of the signal line 20 in the region over which the low dielectric region 40 extends is larger than the width dimension of the signal line 20 in the other region (insulating resin portion 45) other than the above region. Yes. This is because between the signal line 20 and the ground layer 70, the effective relative permittivity at the location where the low dielectric region 40 is provided tends to be smaller than the effective relative permittivity at the location where the insulating resin portion 45 is provided. Due to being. By adjusting the line width of the signal line 20, it is possible to meet the demand for high-precision impedance matching and to further reduce the transmission loss under high-speed transmission.
As an example, in the case of a differential transmission wiring pair with a signal line spacing of 100 μm, the line width of the first signal line 21 and the second signal line 22 is 160 μm in the wiring region 24 a facing the low dielectric region 40, Each line width can be set to 110 μm in the facing wiring region 24c. Then, the signal line 20 can be created so that the line width continuously changes in the intermediate region 24b between the wiring region 24a and the wiring region 24c. Thereby, a predetermined characteristic impedance (for example, 100Ω) can be realized with high accuracy.

<Manufacturing method>
Hereinafter, the manufacturing method of the printed wiring board 100 of this embodiment is demonstrated. Although this manufacturing method may be described using a plurality of steps described in order, the order of description does not limit the order or timing of performing the plurality of steps. When carrying out this manufacturing method, the order of the plurality of steps can be changed within a range that does not hinder the contents, and some or all of the execution timings of the plurality of steps may overlap each other.

  FIG. 9A to FIG. 9F are process cross-sectional views illustrating a method for manufacturing the printed wiring board 100 of the present embodiment, and represent a cross section of the bent portion 28 illustrated in FIG.

  First, as shown in FIG. 9A, the insulating resin film 170 is formed by forming the adhesive layers 111 and 121 on the front and back surfaces of the insulating resin layer 60. For the insulating resin layer 60, a resin sheet such as polyimide having a thickness of about 25 μm can be used. As a method for forming the adhesive layers 111 and 121, a coating method such as die coating, a method of laminating an adhesive sheet, or the like can be selected. A low flow bonding sheet having a thickness of about 5 μm can be used as the adhesive sheet.

  Thereafter, as shown in FIG. 9B, a low dielectric region (void) 40 is formed by a method such as punching the insulating resin film 170 at a predetermined size and position with a mold. As a method for forming the low dielectric region (void portion) 40, methods such as laser processing, plasma irradiation, drilling, and wet etching can be applied alone or in combination in addition to punching with a mold.

  In this manufacturing method, the low dielectric region 40 is formed before the conductor layers such as the signal layer 25 and the ground layer 70 are laminated. For this reason, it is easy to form the void portion, and there is no possibility of damaging other layers when the void portion is formed.

  In the bent portion 28, a part of the width dimension of the insulating resin film 170 including a region where the first signal line 21 is to be formed is punched to form a void portion. The low dielectric region (gap portion) 40 of the present embodiment is formed of the insulating resin film 170 in consideration of the cut-off regions at both ends in the width direction and the width dimension left as the insulating resin portion 45 in the planned formation region of the second signal line 22. It is formed to be about one third of the width dimension.

  Next, as shown in FIG. 9 (c), two single-sided copper-clad laminates in which a copper foil layer 116 is attached to one side of an insulating substrate 112 (for example, a polyimide film having a thickness of 12.5 μm) are prepared. To do. The single-sided copper-clad laminate is aligned so that the insulating base material 112 is located on both sides of the insulating resin film 170, and is temporarily attached by the adhesive layers 111 and 121 to be laminated. As a result, the low dielectric region (void portion) 40 is closed. By using a flat plate press for lamination, it is possible to prevent unnecessary adhesive from flowing out. The copper foil layer 116 on one side (the upper surface side in the figure) is used not only for the signal layer 25 but also for the copper foil layer 115 serving as a base for the ground pad 30. The copper foil layer 116 on the other side (the lower surface side in the figure) is used for the copper foil layer 123 that is the base of the ground layer 70 (see FIG. 3).

  Next, a through hole 90 (see FIG. 3) for making interlayer connection between the copper foil layers 116 on both sides is created. The through-hole 90 can be formed as a non-through bottomed via hole by laser machining or the like, in addition to a through-through hole by an NC drill. In this embodiment, the through-holes are subjected to a conductive treatment and electrolytic copper plating so that the plating layers 114 and 117 are formed on the inner peripheral surface of the through-hole 90 and the surfaces of the copper foil layers 116 (including 115 and 123). To form. Thereby, conduction between the copper foil layers 116 on both sides is obtained.

  Further, as shown in FIG. 9D, necessary patterns such as the first signal line 21, the second signal line 22, and the ground pad 30 are formed on the upper surface of the copper foil layer 116 (115) by photolithography. It is formed by the method. A pattern of the ground layer 70 is also formed on the copper foil layer 116 (123) on the lower surface side by a photolithography method or the like. Through the above steps, the substrate 180 having the low dielectric region 40 in which the signal layer 25 and the ground layer 70 are patterned on both surfaces is obtained.

  Next, after forming protective layers 80 on both sides of the substrate 180 as shown in FIG. 9 (e), outer shape processing is performed as shown in FIG. 9 (f), and the low dielectric region 40 and the insulating resin portion 45 are formed. The substrate 180 is cut along cut lines that pass through each. Thereby, a printed wiring board 100 having a microstrip line structure (differential transmission line) having a low dielectric region 40 is obtained. By this outer shape processing, the end face of the low dielectric region (void portion) 40 is released and becomes an opening 50.

  According to this manufacturing method, since the signal line 20 and the ground layer 70 are laminated before the opening 50 that communicates with the outside of the gap portion, the chemical solution used during this period and dust generated during this time enter the gap portion. You can avoid that. Since the opening 50 is formed by the outer shape processing of the substrate 180, it is not necessary to prepare a special process for making the low dielectric region (void portion) 40 communicate with the outside.

<Second embodiment>
10 (a) to 10 (f) are process cross-sectional views illustrating a method for manufacturing the printed wiring board 100 according to the second embodiment of the present invention, and represent a cross-section of the bent portion 28 illustrated in FIG.

  The printed wiring board 100 of the present embodiment is first in that the low dielectric region 40 is filled with another resin material having a lower dielectric constant than the resin material (insulating resin portion 45) constituting the insulating resin layer 60. This is different from the embodiment (see FIG. 10F).

  As in the first embodiment, the insulating resin portion 45 is made of a thermosetting resin such as an epoxy resin or a thermoplastic resin such as a liquid crystal polymer in addition to a polyamide resin such as a polyimide resin, a polyamide resin, or a polyamideimide resin. be able to. The relative dielectric constant of the insulating resin portion 45 is preferably 3 or more. Specifically, a polyimide resin (relative dielectric constant: about 3.0 or more and about 4.5 or less) or a liquid crystal polymer (relative dielectric constant: about 3.0 or more and about 3.5 or less) can be suitably used.

  Other resin materials (low dielectric resin) filled in the low dielectric region 40 include thermoplastic resin materials such as polyphenylene ether (PPE), polyethylene (PE), polytetrafluoroethylene (PTFE), and modified polyphenylene ether ( m-PPE). The low dielectric resin used for the low dielectric region 40 preferably has a relative dielectric constant of less than 3. The relative dielectric constant of PPE or m-PPE is about 2.5, the relative dielectric constant of PE is about 2.3, and the relative dielectric constant of PTFE is about 2.1.

  The low dielectric region 40 of the present embodiment is formed by filling the gap formed in the insulating resin layer 60 with a low dielectric resin. As a manufacturing process of the printed wiring board 100, a gap is formed in the insulating resin layer 60 before the insulating base materials 112 and 122 and the conductor layers (the signal layer 25 and the ground layer 70) are formed, and the low dielectric region 40 is filled therein. The pre-filling method to perform can be illustrated.

  First, as shown in FIG. 10A, a sheet-like insulating resin layer 60 is prepared. A gap is formed at a predetermined position of the insulating resin layer 60 by a method such as punching, and a sheet-like low dielectric resin formed in the same shape is fitted into the gap, or a liquid low dielectric resin is inserted into the gap. Insulating resin film 170 is created by coating (see FIG. 10B). The insulating resin film 170 of this embodiment is a composite resin sheet in which a plurality of resin materials (insulating resin portion 45 and low dielectric resin) having different relative dielectric constants are combined in the in-plane direction.

  As shown in FIG. 10C, the adhesive layers 111 and 121, the insulating base materials 112 and 122, and the copper foil layer 116 are laminated on the front and back surfaces of the insulating resin film 170 in order from the inside. The material of each layer can be the same as in the first embodiment.

  Thereafter, similarly to the first embodiment, after the interlayer connection of the copper foil layer 116 is performed through the through hole 90, the plating layers 114 and 117 are formed (see FIG. 3). Next, as shown in FIG. 10 (d), the first signal line 21, the second signal line 22 and the ground pad 30 (see FIG. 3) are patterned to form a substrate 180, and protective layers 80 are formed on both sides. (See FIG. 10E). Finally, as shown in FIG. 10 (f), external processing is performed, and the printed wiring board 100 is obtained by cutting both sides of the substrate 180 in the width direction. By this external processing, the low dielectric region 40 is cut and the low dielectric resin is exposed on the end face of the printed wiring board 100.

  By using the manufacturing method described above, since there is substantially no void in the printed wiring board 100 in the outer shape processing step, the printed wiring board 100 has high strength in the thickness direction. For this reason, the printed wiring board 100 which is excellent in workability and dimensional stability can be obtained.

The present invention is not limited to the above-described embodiment, and includes various modifications and improvements as long as the object of the present invention is achieved.
For example, the printed wiring board 100 shown in FIG. 1 has a planar shape in which two bent portions 28 are connected by a straight portion 26, but the present invention is not limited to this. For example, both ends of the printed wiring board 100 of FIG. 1 may be further curved inward. As a result, there are a total of four bent portions 28, and the line length of the first signal line 21 on the outer peripheral side is further longer than that of the second signal line 22.

<Example>
Hereinafter, regarding the first embodiment and the second embodiment, the signal propagation time between the first signal line 21 on the outer peripheral side and the second signal line 22 on the inner peripheral side of the bent portion 28 by the printed wiring board 100 having general dimensions. Explain that T can be equalized.

As the shape of the printed wiring board 100, as shown in FIG. 1, a rounded U-shaped signal line having two planar bent portions 28 (28a and 28b) is illustrated. The second signal line 22 has no meander wiring. The total central angle of the bent portions 28a and 28b is 180 degrees.
The curvature radius R of the first signal line 21 positioned on the outer peripheral side is 30 mm, and the curvature radius R of the second signal line 22 positioned on the inner peripheral side is 29.5 mm. The length of the straight line portion 26 is common to the first signal line 21 and the second signal line 22. Thereby, the length from the one end 21a to the other end 21b of the first signal line 21 is longer by π / 2 (≈1.57 mm) than the length from the one end 22a to the other end 22b of the second signal line 22. Become. That is, when the line length of the second signal line 22 is 300 mm, the line length of the first signal line 21 is 301.57 mm.

  The insulating resin layer 60 (insulating resin portion 45) is made of polyimide resin having a relative dielectric constant = 3.25, and the low dielectric region 40 is made of air (relative dielectric constant≈1) or low dielectric resin. As the low dielectric resin, PPE (relative permittivity≈2.5), PE (relative permittivity≈2.3), and PTFE (relative permittivity≈2.1) were used.

  Table 1 below shows the effective relative dielectric constant (apparent dielectric constant) ε and the propagation velocity τ determined by the above equation (2). The effective relative dielectric constant ε of each case was calculated by weighted averaging the physical property value of the relative dielectric constant and the relative dielectric constant of the insulating resin portion 45 with a weight ratio of 50%.

  From Table 1, the propagation speed τ when the low dielectric region 40 facing the signal line 20 is air is about 0.21 mm / psec, which is 0 than the propagation speed τ of the signal line 20 facing the insulating resin portion 45. It was found that the speed was increased by about .04 mm / psec. Similarly, it was found that the propagation speed τ is increased when the low dielectric region 40 is filled with a low dielectric resin.

For the above case, the minimum required length L ₂ of the low dielectric region 40 for the signal propagation time T obtained by the above equation (3) to be equal between the first signal line 21 and the second signal line 22 is as follows: It shows in Table 2. In other words, how long the first signal line 21 located on the outer peripheral side of the bent portion 28 is opposed to the low dielectric region 40 as compared with the second signal line 22 so that the line length is longer by 1.57 mm. We asked whether the signal delay due to can be canceled.

From the results of Table 2, when the low dielectric region 40 is a gap (air), the first signal line 21 is opposed to the low dielectric region 40 over the line length of 8.21 mm. It was found that the signal propagation times T of the line 21 and the second signal line 22 can be made equal. In other words, as compared to the length _{L 22} that faces the low dielectric region 40 of the second signal line 22, to as long as 8.21mm low dielectric region 40 opposed to the length _{L 21} of the first signal line 21 This means that the signal propagation time T becomes equal.
Further, when the low dielectric region 40 is a low dielectric resin (PPE, PE, PTFE), the first signal line 21 extends over the line lengths of 26.4 mm, 20.7 mm, and 16.9 mm, respectively. It has been found that the signal propagation times T of the first signal line 21 and the second signal line 22 can be made equal by facing each other.

  That is, in the case where the low dielectric region 40 is not disposed immediately below the second signal line 22, the line is only a few percent (8.21 mm to 26.4 mm) of the line length (301.57 mm) of the first signal line 21. By facing the low dielectric region 40 by the length, the signal propagation times T of the first signal line 21 and the second signal line 22 can be made equal.

In the case of the printed wiring board 100 of the present embodiment, the line length of the first signal line 21 at the two bent portions 28a and 28b having the curvature radius R = 30 mm is about 94 mm, which is necessary for the low dielectric region 40. It is greater than the length _{L 2.} Therefore, in the case where the low dielectric region 40 is made of either air or low dielectric resin, the signal propagation times T of the first signal line 21 and the second signal line 22 are equal only within the length region of the bent portion 28. Is possible.

That is, the length L _{21 of the} portion of the first signal line (first signal line 21) facing the low dielectric region 40 and the low dielectric region of the second signal line (second signal line 22). The difference from the length L _{22 of the} portion facing 40 can be made smaller than the length of the bent portion 28. When the first signal line 21 or the second signal line 22 faces the low dielectric region 40 at a plurality of locations discretely arranged along the signal line 20, the length L ₂₁ and the length L described above are used. ₂₂ is the total of the opposing lengths of the plurality of locations.

  According to the printed wiring board 100 of the present embodiment, the low dielectric region 40 is formed in a partial region of the length of the bent portion 28 and is opposed to the first signal line 21, thereby extending the entire length of the signal line 20. It is possible to prevent signal delay from occurring in the first signal line 21 on the outer peripheral side. Therefore, even if external noise such as electromagnetic waves is mixed in any position of the signal line 20 including not only the straight line portion 26 but also the bent portion 28, the noise signal does not delay and the first signal line 21 and the second signal line 21 are not delayed. It is transmitted through the signal line 22 and input to the receiver. For this reason, this noise signal can be easily removed by acquiring the voltage amplitude difference with the receiver (see FIG. 11A). Further, since the signal delay between the first signal line 21 and the second signal line 22 can be eliminated only by the bending portion 28, the low dielectric region 40 can be formed in the linear portion 26 at an arbitrary ratio. For this reason, the printed wiring board 100 can suppress the effective relative dielectric constant of the insulating resin layer 60 as a whole, and enables high-speed signal transmission.

As described above, in the embodiment and the example, the case where the plurality of bending portions 28 are bent or bent in the same direction is illustrated, but the present invention is not limited thereto. In the printed wiring board 100, a plurality of bent portions 28 may be bent in opposite directions. The line lengths of the first signal line 21 and the second signal line 22 may be equal as a whole. When the line lengths of the first signal line 21 and the second signal line 22 are equal as a whole, the signal output from the driver is received by the receiver (FIG. 11 (a)) even if the bent portion 28 is provided in the middle of the signal line 20. See) at the same time. Therefore, noise mixed in the input signal output from the driver is naturally removed by the difference processing of the receiver. However, even in this case, every time the signal passes through the bent portion 28, signal delay occurs alternately in the signal line 20 on the outer peripheral side and the inner peripheral side. Therefore, when external noise such as electromagnetic waves is mixed in the signal line 20, the noise cannot be removed by differential processing of the receiver depending on the mixing position.
On the other hand, according to the printed wiring board 100 of the present embodiment and the example, since the signal delay is eliminated in the bent portion 28, the arbitrary position regardless of the number of the bent portions 28 and the direction of bending or bending. Even if external noise is mixed in, it can be removed by differential processing of the receiver.

  Each component of the printed wiring board 100 of the present invention described above does not have to be individually independent. A plurality of components are formed as one member, a component is formed of a plurality of members, one component is a part of another component, and one component is And a part of other components are allowed to overlap.

The above embodiment includes the following technical idea.
(1) A signal layer in which at least a pair of parallel differential transmission signal lines are formed, a conductor layer provided to face the signal lines, and an insulating resin sandwiched between the signal layer and the conductor layer A pair of the signal lines having a bent portion that is curved or bent in a plane of the signal layer, the first signal line positioned on the outer peripheral side of the bent portion, and the bent portion And the second signal line having a line length shorter than that of the first signal line, and the insulating resin layer is located at a position facing the first signal line. A printed wiring board, wherein a low dielectric region having a lower dielectric constant is provided.
(2) The signal propagation time represented by the following expression (1) until the signal passes from one end to the other end of the first signal line and the second signal line is equal to each other ( Printed wiring board according to 1);
T = (L ₁ · √ (ε ₁ ) + L ₂ · √ (ε ₂ )) / C ₀ (1)
However, T is the signal propagation time of the first signal line or the second signal line, and L ₁ is a length of the line length of the first signal line or the second signal line facing the insulating resin layer. L ₂ is the length of the first signal line or the second signal line facing the low dielectric region, ε ₁ is the effective relative dielectric constant of the region where the insulating resin layer is formed, ε ₂ is an effective relative dielectric constant of the formation region of the low dielectric region, and C ₀ is the speed of light.
(3) The length of the first signal line facing the low dielectric region is greater than the length of the second signal line facing the low dielectric region. ) Printed wiring board.
(4) The low dielectric region is provided to face the bent portion of the first signal line, and the low dielectric region does not face the second signal line. ) Printed wiring board.
(5) The difference between the length of the first signal line facing the low dielectric region and the length of the second signal line facing the low dielectric region is smaller than the length of the bent portion. The printed wiring board according to (3) or (4) above.
(6) In any one of the above (1) to (5), the low dielectric region is provided at both a position facing the bent portion and a position facing the linear portion in the first signal line. The printed wiring board as described.
(7) The above-described (6), wherein the planar view shape of the low dielectric region provided at a position facing the bent portion of the first signal line is a taper shape that becomes wider toward the outer peripheral side of the bent portion. Printed wiring board as described in 1.
(8) The above-described (1), wherein the pair of signal lines includes a plurality of the bent portions that are bent or bent in the same direction, and the low dielectric region is provided to face each of the plurality of bent portions. The printed wiring board according to any one of (7) to (7).
(9) The line width of the first signal line continuously increases from a region facing the insulating resin layer to a region facing the low dielectric region. The printed wiring board as described in any one of Claims.
(10) The low dielectric region is filled with another resin material having a dielectric constant lower than that of the resin material constituting the insulating resin layer, according to any one of (1) to (9) above. Printed wiring board.
(11) The printed wiring board according to any one of (1) to (9), wherein the low dielectric region is a gap provided in the insulating resin layer.
(12) The printed wiring board according to (11), wherein the low dielectric region includes a vent hole communicating with the outside.

DESCRIPTION OF SYMBOLS 10 Insulation layer 20 Signal line 21 1st signal line 22 2nd signal line 21a, 22a One end 21b, 22b The other end 24a, 24c Wiring area | region 24b Middle area | region 25 Signal layer 26 Linear part 28, 28a, 28b Bending part 30 Ground pad 40 Low dielectric region 45 Insulating resin part 50 Opening 60 Insulating resin layer 70 Ground layer 80 Protective layer 90 Through hole 100 Printed wiring board 111/121 Adhesive layer 112/122 Insulating base material 114/117 Plating layer 115, 116, 123 Copper foil layer 170 Insulating resin film 180 Substrate

Claims (11)

A signal layer in which at least a pair of parallel differential transmission signal lines are formed, a conductor layer provided facing the signal line, an insulating resin layer sandwiched between the signal layer and the conductor layer, With
The pair of signal lines has a bent portion that is bent or bent in the plane of the signal layer, and is positioned on the inner peripheral side of the bent portion and the first signal line positioned on the outer peripheral side of the bent portion. And the second signal line having a line length shorter than that of the first signal line,
The insulating resin layer is provided with a low dielectric region having a dielectric constant lower than that of the insulating resin layer at a position facing the first signal line .
The printed wiring board , wherein the low dielectric region is a gap provided in the insulating resin layer and includes a vent hole communicating with the outside . The signal propagation time represented by the following expression (1) until the signal passes from one end to the other end of the first signal line and the second signal line is equal to each other. Printed wiring board;
T = (L ₁ · √ (ε ₁ ) + L ₂ · √ (ε ₂ )) / C ₀ (1)
Where T is the signal propagation time of the first signal line or the second signal line,
L ₁ is the length that is opposite the insulating resin layer of the line length of the first signal line or the second signal line,
L ₂ is the length of the first signal line or the second signal line that is opposed to the low dielectric region,
ε ₁ is an effective relative dielectric constant of a region where the insulating resin layer is formed,
ε ₂ is the effective relative dielectric constant of the formation region of the low dielectric region,
C ₀ is the speed of light.   The printed wiring according to claim 1, wherein a length of the first signal line facing the low dielectric region is larger than a length of the second signal line facing the low dielectric region. Board.   The low dielectric region is provided so as to face the bent portion of the first signal line, and the low dielectric region does not face the second signal line. Printed wiring board.   The difference between the length of the first signal line facing the low dielectric region and the length of the second signal line facing the low dielectric region is smaller than the length of the bent portion. Or the printed wiring board of 4.   6. The printed wiring board according to claim 1, wherein the low dielectric region is provided at both a position facing the bent portion and a position facing the linear portion in the first signal line. 7.   7. The print according to claim 6, wherein a planar view shape of the low dielectric region provided at a position facing the bent portion of the first signal line is a taper shape that becomes wider toward an outer peripheral side of the bent portion. Wiring board.   The pair of the signal lines has a plurality of the bent portions that are bent or bent in the same direction, and the low dielectric region is provided to face each of the plurality of the bent portions. The printed wiring board as described in any one of Claims.   9. The line width of the first signal line continuously increases from a region facing the insulating resin layer to a region facing the low dielectric region. Printed wiring board. The printed wiring board according to any one of claims 1 to 9, wherein the gap portion is formed on a side end surface in a thickness direction of the insulating resin layer and communicates with the outside .   The printed wiring board according to claim 10, wherein the gap formed on the side end surface and communicating with the outside is provided at a position facing the bent portion of the first signal line in the insulating resin layer. .

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