JP2018019063A - Printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printed wiring board capable of maintaining the characteristics of a coil, such as the Q, in good state even if the coil is mounted.SOLUTION: A board has a base material of nonconductor, and a conductor layer formed on the surface of the base material. In a region where a coil is mounted, a removal part from which the conductor layer was removed is formed. The removal part is formed with a width narrower than that of the coil across the axial direction thereof. Since many magnetic fluxes pass the conductor removal part where there is no copper foil, decrease of Q due to eddy current can be minimized, even if a current is fed to the coil.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a printed wiring board on which a coil is mounted.

  The printed wiring board is obtained by forming a conductor layer such as a copper foil on one side or both sides of a base material such as glass epoxy. When a coil is mounted on this printed wiring board, the conductor layer may affect the characteristics of the coil. When a current flows through the coil, a magnetic flux is generated. When this current changes, the generated magnetic flux also changes. When the changing magnetic flux crosses the conductor layer, an eddy current is generated in the conductor layer, and the eddy current creates a new magnetic field. Since this magnetic field acts in a direction that cancels the magnetic field of the coil, this increases the electrical resistance (DC resistance component) R of the coil, and Q (Q = ωL / R, L: coil inductance that is an index indicating the characteristics of the coil) (H), R: Electric resistance (Ω) of the coil is lowered. Further, the inductance of the coil is also reduced by the eddy current.

JP 2008-0344415 A

  In order to solve the above problem, a proposal as in Patent Document 1 has been conventionally made. In the printed circuit board of Patent Document 1, generation of a large eddy current is suppressed by dividing a conductor pattern at a position on the board on which the choke coil is mounted into a plurality of regions.

  However, even if the conductor pattern is divided into a plurality of regions as in Patent Document 1, since the eddy current is generated in each divided region, the effect of suppression is limited. In addition, it is impossible to prevent a change in inductance due to the conductor layer.

  An object of the present invention is to provide a printed wiring board capable of maintaining the coil characteristics in a good state.

  The printed wiring board of the present invention includes a non-conductive base material, a conductor layer formed on the surface of the base material, a region in which the coil is mounted in the conductor layer, and the base material in the region and the conductor layer of the coil. And a removal portion removed over the axial direction of the coil with a width narrower than the width.

  In the present invention, a non-magnetic non-conductive plate may be provided between the coil and the removal portion, and the coil may be mounted in parallel with the conductive layer.

  The printed wiring board of the present invention may be used for a crossover circuit of a speaker system.

  In the printed wiring board of the present invention, it is possible to minimize the deterioration of characteristics such as Q of the mounted coil.

It is a top view of the printed wiring board to which this invention is applied. It is a figure which shows the form by which a coil is mounted in a printed wiring board. It is a figure which shows the magnetic flux which arises when an electric current flows into a coil. It is a figure which shows the modification in the case of mounting a coil on a printed wiring board. It is the figure which illustrated the conductor removal part formed with respect to the coil which has an axis | shaft perpendicular | vertical to a board | substrate.

  A printed wiring board (hereinafter referred to as a board) 1 according to an embodiment of the present invention will be described with reference to the drawings. A substrate 1 shows an example of a substrate for a crossover circuit of a speaker system. The crossover circuit is a circuit for supplying a speaker drive signal input from an audio amplifier through a speaker cable to two speaker units (2 ways) or three speaker units (3 ways). In the 2-way speaker system, a high-frequency range speaker unit and a low-frequency range speaker are used, and the speaker drive signal is divided into two frequency bands, a high-frequency range and a low-frequency range. In the 3-way speaker system, a high-frequency range speaker, a mid-range range speaker, and a low-range range speaker are used, and the speaker drive signal is divided into three frequency bands, a high-frequency range, a mid-range range, and a low-range range. The crossover circuit of this embodiment includes only passive components such as a coil, a capacitor, and a resistor, and is called a passive crossover circuit. Speaker drive signals have characteristics such as low frequency (audio frequency), low impedance, and relatively large current. Therefore, in a crossover circuit, a wide circuit pattern with low electrical resistance and a coil with high inductance that can filter low frequencies Etc. are used.

  In FIG. 1, a substrate 1 is a double-sided substrate in which copper foils 2 and 3 as conductor layers are formed on the front and back surfaces of a base material 4 made of a nonconductor such as glass epoxy. A plurality of (four in the drawing) mounting regions 10, 20, 30, and 40 are formed on the substrate 1. Filter coils are mounted in the mounting regions 10, 20, 30, and 40. Coils having axes parallel to the substrate 1 are mounted in the mounting regions 10, 20, 30, and 40. Although other components are also mounted on the substrate 1, a circuit pattern is formed on the copper foils 2 and 3 of the substrate 1, but these are not shown for simplicity of explanation. Yes.

  An example of a coil mounted on the substrate 1 is shown in FIG. The illustrated coil 50 is a coil mounted on the mounting region 10, for example. The coil 50 is obtained by winding a copper wire 51 around a bobbin 52 having flanges 53 and 54 at both ends. An iron core 55 is provided inside the bobbin 52 so that a high inductance can be obtained with a small number of windings. Both ends of the copper wire 51 are inserted into connection holes (via holes) 60 formed in the substrate 1 as lead wires and fixed by soldering. In addition, two binding holes 61 that are through holes are formed on both sides of the mounting region 10. After the coil 50 is placed on the mounting area 10, the substrate 1 and the coil 50 are bound by binding the coil 50 with a binding band 62 such as Insulok (registered trademark) passed through the binding hole 61.

  Here, the coil 50 mounted in the mounting area 10 has been described, but the coils mounted in other mounting areas and the mounting forms thereof are substantially the same. However, the coil mounted in the mounting region 30 is a hollow coil having no iron core.

  FIG. 3 is a diagram illustrating a magnetic flux formed when a current is passed through the coil 50. The coil 50 is mounted on the substrate 1. Copper foils 2 and 3 are formed on the front and back of the substrate 1. When a current is passed through the coil 50, a magnetic flux 70 is generated that penetrates the inside of the coil 50 in the axial direction and circulates around the periphery. The magnetic flux 70 is formed at a high magnetic flux density inside the coil 50 (iron core 55) from the S pole (flange 53 side in the drawing) to the N pole (flange 54 side in the drawing), and from the N extreme portion outside the coil. Go around the coil and return to the S extreme. Magnetic flux that circulates on the substrate side penetrates the substrate from the front to the back near the N pole and penetrates from the back to the front near the S pole.

  In a normal substrate, copper foils 2 and 3 are also formed below the coil 50. Since the speaker drive signal is an audio signal (alternating current), the magnetic flux across the copper foils 2 and 3 changes. When the magnetic flux across the copper foils 2 and 3 changes, an eddy current is generated in the copper foils 2 and 3. This eddy current generates a magnetic flux in a direction opposite to that of the coil 50. The current value of the coil 50 decreases due to the mutual induction by the magnetic flux in the opposite direction. As a result, the resistance value R of the coil 50 increases, and Q (Q = ωL / R), which is a value indicating the performance of the coil, decreases. Further, the inductance L of the coil 50 also decreases due to the influence of mutual induction caused by eddy current.

  Therefore, in this embodiment, as shown in FIGS. 1 and 2, a part or all of the copper foils 2 and 3 in the mounting region 10 are removed to form conductor removal portions 11 and 12. As a result, there is no conductor in the region where the magnetic flux 70 of the coil 50 passes at a high density, and it is possible to prevent a decrease in Q due to mutual induction due to eddy currents and a change in inductance. The conductor removing portions 11 and 12 may be formed by removing the copper foils 2 and 3 from the base material 4 by etching or peeling. Moreover, you may form the opening part of the board | substrate 1 as the conductor removal parts 11 and 12. FIG. That is, the base material 4 may be cut out together with the copper foils 2 and 3 to form conductor removal portions 11 and 12.

  The conductor removal portion may be formed over the entire axial direction of the coil, like the conductor removal portion 41 in the mounting region 40. On the other hand, like the conductor removal parts 11 and 12 of the mounting area | region 10, you may make it not form in the position corresponding to the center part of a coil, although it forms in the front and back both ends of the axial direction of a coil. As shown in FIG. 3, the magnetic flux traversing the substrate 1 is small at the corresponding position in the central portion of the coil, so even if the copper foils 2 and 3 are left, there is little adverse effect on the Q of the coil.

  Below, the experiment example which measured the change of the inductances L and Q at the time of mounting a coil on a printed wiring board is shown. When a coil containing a certain silicon steel plate (L = 30.18 mH was held in the air and a signal of 1 kHz and 1 V was input to this coil, Q was 29.5. That is, the electric resistance R was about 6.4Ω. When this coil was mounted on a normal board (a board in which copper foil was also left in the mounting area), the inductance L dropped to 29.74 mH, and the same 1 kHz, 1 V signal as above was input. As a result, Q was extremely reduced to 15.3, that is, the electric resistance R was almost doubled (12.21Ω) On the other hand, when this coil was mounted on the mounting region 10 of the substrate 1, the inductance L was 30. When the same 1 kHz, 1 V signal was input as above, Q was able to be suppressed to a slight decrease of 26.8, and the electric resistance R at this time was 7.06Ω. .

  As described above, in the substrate 1 of the present embodiment, the Q of the mounted coil and the change in the inductance L can be minimized.

  In FIG. 1, in the mounting region 10, the conductor removing portions 11 and 12 are formed within the range of the mounting region 10. Further, it may be formed so as to protrude from the mounting region 20 like the conductor removal portions 21 and 22 in the mounting region 20. The conductor removal portions 21 and 22 are formed beyond the mounting region 20 in the axial direction (longitudinal direction) of the coil. As shown in FIG. 3, in the axial direction of the coil, a high density magnetic flux may pass beyond the mounting area, so the copper foils 2 and 3 at positions exceeding the mounting area 20 in the axial direction should be removed. Is effective in improving the Q of the coil.

  In FIG. 1, no conductor removal portion is formed in the mounting region 30. As described above, the hollow coil is mounted in the mounting region 30. This is because the hollow coil generally has a smaller inductance L (less magnetic flux generated) than a coil with iron core, and thus is considered to be less affected by eddy currents. Further, since the hollow coil has a higher Q than the iron cored coil, it is considered that even if the performance is somewhat degraded by eddy current, the influence on the entire circuit is small.

  FIG. 4 is a diagram showing a modified example in which the decrease in Q is further suppressed. In addition to forming the conductor removal portions 11 and 12 in the mounting region 10, the plate 80 may be sandwiched between the coil 50 and the substrate 1 as shown in FIG. The plate 80 is preferably non-conductive and non-magnetic (preferably close to the permeability of air). As the plate 80, for example, crow epoxy, wood, glass, resin, ceramics and the like are applicable. As a result, the distance between the copper foils 2 and 3 and the coil 50 becomes longer, so that the Q of the mounted coil 50 and the change in the inductance L can be kept smaller. Further, as described above, when the conductor removing portions 11 and 12 are formed by cutting the substrate 1, the plate 80 also serves as a reinforcement of the substrate 1.

  In the above embodiment, the case where the coil 50 having a horizontal axis is mounted on the substrate has been described. However, other angles may be used. For example, as shown in FIG. 5, the present invention can also be applied when a coil 57 having a vertical axis is mounted on the substrate 1. Even in this case, it is preferable to form the conductor removal portion 58 at the position where the coil 57 is mounted and the peripheral portion thereof.

  In this embodiment, with the coil mounting area as a reference, the conductor removal portion is formed within that range or at a portion exceeding the mounting area in the axial direction of the coil. As another method, an area where the magnetic flux density passing through the substrate is a predetermined value or more is obtained by observing the magnetic flux of the coil to be mounted, and the conductor removal portion may be formed in this area.

  In the above embodiment, it is assumed that the same shape of the conductor removal portion is formed on the front copper foil 2 and the back copper foil 3, but the copper foils 2 and 3 have different shapes. A conductor removal portion may be formed. The present invention can also be applied to a single-sided substrate.

1 Printed wiring board (board)
2,3 Copper foil (conductor layer)
4 Substrate 10, 20, 30, 40 Mounting area 11, 12, 21, 22, 41 Conductor removal part 50 Coil 51 Copper wire 53, 54 Flange 55 Iron core 60 Connection hole 61 Binding hole

Claims (4)

A non-conductive substrate;
A conductor layer formed on the surface of the substrate;
A region in which the coil is mounted in the conductor layer;
The base material and the conductor layer in the region have a width narrower than the width of the coil, and are removed over the axial direction of the coil; and
Printed wiring board with   The printed wiring board according to claim 1, wherein the coil is mounted in parallel with the conductor layer.   The printed wiring board according to claim 1, wherein a nonmagnetic non-conductive plate is provided between the coil and the removal portion.   The printed wiring board according to claim 1, which is a board for a crossover circuit of a speaker system.

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