JP2009194007A - Noise control structure for ceramic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a structure for reducing noise generated by a ceramic capacitor mounted on a printed wiring board. <P>SOLUTION: The ceramic capacitor 100 is mounted on a surface of the printed wiring board 200. Expansion/contraction suppressing members 209, 211, 213, 215, 217, 219, and 221 are disposed around the ceramic capacitor in various forms. The expansion/contraction suppressing members are fixed to the surface of the printed wiring board. When the ceramic capacitor vibrates through piezoelectric effect and then the printed wiring board also vibrates, the expansion/contraction suppressing members suppress expansion/contraction motion of the surface of the printed wiring board to suppress vibrations and noise. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a technique for reducing noise generated from a printed wiring board on which a ceramic capacitor is mounted.

  Capacitors used in electronic equipment include ceramic capacitors, tantalum electrolytic capacitors, aluminum electrolytic capacitors, and film capacitors. There is a single-layer type ceramic capacitor composed of a pair of electrodes, but many are multilayer ceramic capacitors having a structure in which a plurality of electrode pairs are stacked. Ceramic capacitors can be manufactured in a small size because the dielectric constant of the dielectric is large, and since the capacitance change with time is small, many ceramic capacitors are used in recent electronic devices. A ceramic material used for a ceramic capacitor exhibits ferroelectricity, and a so-called piezoelectric phenomenon or electrostriction phenomenon occurs in which mechanical distortion occurs when voltage is applied to both ends of the ceramic material.

  Ceramic capacitors generally use a high dielectric constant ferroelectric material made mainly of barium titanate (BaTiO3). This dielectric has a perovskite-type crystal structure, and in the sintered state, spontaneous polarization occurs inside and the crystal grains are oriented in random directions. Even if an electric field is applied to the ferroelectric in this state from the outside, the piezoelectric effect of each crystal grain is offset, and the ferroelectric as a whole does not exhibit piezoelectricity.

  However, when a high DC voltage is applied to this ferroelectric, each crystal grain is polarized in the direction of the electric field and exhibits piezoelectricity. The computer is equipped with a DC / DC converter, and a predetermined DC voltage is supplied to each electronic device. In the input / output circuit of the DC / DC converter, a ripple voltage in the audible frequency range is generated by the switching operation. Therefore, a decoupling capacitor is usually connected to the input / output circuit of the DC / DC converter and the power supply circuit of the electronic device in order to reduce noise.

  The decoupling capacitor is applied with a voltage in which an AC voltage that causes noise is superimposed on the DC voltage, so that an inverse piezoelectric effect corresponding to the AC component of the electric field is generated and the capacitor body has its natural frequency. Resonates and vibrates. When a ceramic capacitor is mounted on a printed circuit board (PCB), vibration is transmitted to the PCB and noise is generated.

  Patent Document 1 discloses a technique for suppressing vibration noise generated by an electrostriction phenomenon of a ceramic capacitor attached to an electric circuit board. The electric circuit board is screwed to the frame on the extension of the line connecting the terminal electrodes of the ceramic capacitor and as close to the capacitor as possible. Patent Document 2 discloses a technique for suppressing vibration of an electrical component mounted on a circuit board of an audio amplifier. The entire back surface of the circuit board is fixed in close contact with a highly rigid heat dissipation block.

  Patent Document 3 discloses a technique for reducing vibration noise generated when the vibration of the first and second ceramic capacitors generated by the ripple component based on charge / discharge is transmitted to the circuit board and the circuit board is excited. To do. The first and second ceramic capacitors are arranged side by side on the one side of the circuit board, and the amplitude operation of the vibration wave transmitted to the circuit board has a substantially equal phase relationship on the one side of the circuit board. Yes.

Patent Document 4 discloses a ceramic capacitor having a structure that suppresses transmission of vibration to a circuit board. The ceramic capacitor element has a dielectric substrate, a pair of terminal electrodes, and a plurality of internal electrodes. The pair of terminal electrodes are provided at opposite end portions of the dielectric substrate, and each of the plurality of internal electrodes has one end connected to the terminal electrode and the other end being an open end. Each of the pair of metal terminals has a substrate mounting portion and is connected to a corresponding terminal electrode. The substrate mounting portion is on one mounting surface, and the mounting surface intersects the electrode surface of the internal electrode substantially perpendicularly. With this configuration, even if the ceramic capacitor element vibrates due to electrostriction, vibration transmitted to the substrate through the metal terminal can be reduced.
Japanese Patent Laid-Open No. 2002-223082 JP-A-11-145738 Japanese Patent Laid-Open No. 2002-232110 JP 2004-273935 A

  In the above document, the ceramic capacitor is arranged and attached, the circuit board is fixed, the circuit board is fixed, or the heat dissipation block is attached to the circuit board to suppress vibration. Satisfactory results are not always obtained because the constraints are too large. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a noise suppression structure for a ceramic capacitor that can effectively reduce noise with few constraints. Furthermore, the objective of this invention is providing the electronic device which employ | adopted such a noise suppression structure and reduced the noise.

  The noise suppression structure for a PCB according to the present invention includes a ceramic capacitor mounted on the surface of the PCB, and an expansion / contraction suppression member disposed around the ceramic capacitor and fixed to the surface of the PCB. When the vibration of the ceramic capacitor is transmitted to the PCB, the vibration suppressing member suppresses the expansion and contraction movement of the surface of the PCB, thereby suppressing the vibration and noise of the PCB. It is also expected that the piezoelectric effect can be reduced by suppressing the distortion of the ceramic capacitor by suppressing the vibration of the PCB.

  Since the vibration of the PCB is attenuated at a position away from the ceramic capacitor, it is desirable that the expansion / contraction suppressing member is disposed in a range of a distance shorter than the length of the ceramic capacitor. If the expansion / contraction suppressing member is formed of a material close to a rigid body such as metal or ceramics, the movement in the compression direction and the pulling direction of the PCB can be suppressed, so that the expansion / contraction suppression member can be disposed only on one surface of the PCB. Since the vibration of a ceramic capacitor often occurs strongly in the longitudinal direction or the short direction, it is effective to arrange the expansion / contraction suppression member along the longitudinal direction and / or the short direction of the ceramic capacitor. Noise can be suppressed.

  The expansion / contraction suppression member may be arranged so as to surround the ceramic capacitor. Further, the expansion / contraction suppression member may be disposed on the surface opposite to the mounting surface of the PCB ceramic capacitor. At this time, vibration can be more effectively suppressed by disposing the expansion / contraction suppression member at a position including the projection of the ceramic capacitor on the printed wiring board. When a plurality of ceramic capacitors are arranged, the expansion / contraction suppression member may be disposed so as to surround each ceramic capacitor. The expansion / contraction suppression member may be disposed on the front surface and the back surface of the PCB.

  According to the present invention, it is possible to provide a noise suppression structure for a ceramic capacitor capable of effectively reducing noise with few constraints. Furthermore, according to the present invention, it is possible to provide an electronic apparatus that employs such a noise suppression structure and reduces noise.

  FIG. 1 is a diagram for explaining a connection state between a DC-DC converter and a decoupling capacitor mounted on a notebook personal computer (hereinafter referred to as a notebook PC). The DC-DC converter 15 performs a switching operation in order to convert a DC20V voltage supplied from, for example, an AC adapter into a DC5V. From the secondary side of the DC-DC converter 15, power is supplied to the processor, the LCD, and various electronic devices mounted on the mother board directly or via another DC-DC converter.

  A decoupling capacitor group 11 composed of a plurality of multilayer ceramic capacitors (hereinafter simply referred to as ceramic capacitors) is connected to the primary side of the DC-DC converter 15. The DC-DC converter 15 and the decoupling capacitor group 11 are surface-mounted on a printed wiring board. The decoupling capacitor is also called a bypass capacitor, and reduces the impedance of the line with respect to the high-frequency voltage, and serves to limit the movement of the line charge accompanying the switching operation of the DC-DC converter 15 to a local range. Similarly, a decoupling capacitor group 13 composed of a plurality of ceramic capacitors is also connected to the secondary side of the DC-DC converter 15.

  In one example, a ripple voltage generated at a period corresponding to 1 KHz from the DC-DC converter 15 is superimposed on a direct current of 20 V or 5 V. Therefore, a 1 KHz ripple current flows through the decoupling capacitor groups 11 and 13, and when the microphone is used, 1 KHz noise is observed from around the decoupling capacitor groups 11 and 13. The noise generated from the primary side decoupling capacitor group 11 and its vicinity is larger than the noise generated from the secondary side decoupling capacitor group 13 and its vicinity. This noise difference is caused by the difference in the magnitude of the DC voltage applied to the decoupling capacitor groups 11 and 13 as the base voltage.

  FIG. 2A is a diagram illustrating a state in which the ceramic capacitor is attached to the PCB 200, and FIG. 2B is a diagram illustrating a state of vibration when the ceramic capacitor is surface-mounted on the PCB 200. FIG. The ceramic capacitor 100 includes a pair of external terminals 101a and 101b, a plurality of electrodes 103a and 103b connected to each external terminal, and a dielectric 105 made of barium titanate (BaTiO3). FIG. 2B shows a state in which the ceramic capacitor 100 surface-mounted on the PCB 200 is connected to the DC / DC converter 15 and vibrates.

  The ceramic capacitor 100 is formed by soldering or reflow soldering using a lead-free solder on lands 109a and 109b that are part of the wiring pattern formed on the surface of the PCB 200. External terminals 101a and 101b are directly coupled by fillets 107a and 107b. Therefore, vibration generated in the ceramic capacitor 100 is transmitted to the PCB 200 through the external terminals 101a and 101b, the solder fillets 107a and 107b, and the lands 109a and 109b.

  The PCB 200 is a rigid-type multilayer substrate in which a plurality of conductive layers are stacked. The PCB 200 is normally fixed to the notebook PC housing or metal frame at a plurality of positions, but has a structure that can vibrate in a direction perpendicular to the surface of the PCB 200 as indicated by an arrow 205 except for the fixing point. Noise is generated when the PCB vibrates at an audible frequency as shown in FIG. 2B. At this time, the front surface 201 and the back surface 203 of the PCB 200 perform a so-called expansion / contraction motion in which one of them extends and the other contracts. In this specification, the surface on which the ceramic capacitor 100 is mounted on the PCB 200 is referred to as the front surface, and the surface on which the ceramic capacitor 100 is not mounted is referred to as the back surface.

  In the present invention, attention is paid to the stretching motion of the front and back surfaces of the PCB 200 during vibration, and the vibration and noise of the PCB 200 are suppressed by suppressing this stretching motion. In addition, since the ceramic capacitor 100 and the PCB 200 are fixed by the solder fillets 107a and 107b, by suppressing the vibration of the PCB 200, the distortion due to the DC voltage of the ceramic capacitor 100 is suppressed and the polarization is reduced. It can also be expected that the piezoelectric effect due to the AC voltage is reduced.

  FIG. 3 is a diagram illustrating a structure for suppressing noise caused by a ceramic capacitor. The noise suppression structure of the present invention is realized by an expansion / contraction suppression member fixed to the PCB 200. When the PCB 200 vibrates, expansion and contraction motion occurs simultaneously on the front surface and the back surface, but the expansion / contraction suppression member is attached for the purpose of suppressing the expansion and contraction motion of the front surface and / or the back surface of the PCB 200. When the surface of the PCB 200 expands and contracts, tensile, compressive, and bending stresses are generated in the expansion / contraction suppressing member fixed to the surface. Therefore, the expansion / contraction suppressing member needs to have high rigidity against these stresses.

  The expansion / contraction suppression member is ideally a rigid body, but is formed of a solid material having high rigidity against compression, tension, and bending, such as metal and ceramics. If the expansion / contraction suppression member is a rigid body, the expansion / contraction movement can be suppressed only by fixing it to at least one of the front surface and the back surface of the PCB 200. In a case where the expansion / contraction suppression member is fixed to the front surface and the back surface of the PCB 200 as a pair, the expansion / contraction suppression member can be configured by a member having high rigidity with respect to either stress of compression or tension. The expansion / contraction suppression member has any mass because the rigidity functions, but the greater the mass, the greater the vibration suppression effect.

  The expansion / contraction suppression member needs a predetermined length in the wave propagation direction in order to suppress vibration waves generated in the PCB 200. Since various functional parts such as a chip, a resistance element, a capacitor, and a wiring pattern are arranged on the PCB 200, the space that can be provided for the expansion / contraction suppression member is limited. Therefore, the shape of the expansion / contraction suppression member is preferably an elongated rectangular parallelepiped. Further, the expansion / contraction suppressing member can be configured in a flat plate shape in which the dimension in the height direction of the surface perpendicular to the PCB 200 is increased in order to reinforce the rigidity against the bending stress generated when fixed to the PCB 200.

  Since the expansion / contraction suppressing member needs to reliably receive stress due to vibration of the PCB 200, it is desirable to fix the entire contact surface with the PCB 200 with an adhesive. However, a plurality of positions may be fixed by welding or soldering. Although the expansion / contraction suppression member may be fixed to the casing of the notebook PC, it functions to suppress noise without being fixed. Since the fixing position of the PCB 200 with respect to the housing cannot be determined freely, the expansion / contraction suppressing member that does not require fixing with respect to the housing is advantageous in terms of increasing the degree of freedom in designing the PCB 200.

  The vibration generated in the PCB 200 has a larger amplitude in the vicinity of the ceramic capacitor 100, and the surface expansion and contraction is also intense. Therefore, it is desirable to arrange the expansion / contraction suppression member as close to the ceramic capacitor 100 as possible. It is more desirable to dispose the expansion / contraction suppression member so that the distance X between the expansion / contraction suppression member and the ceramic capacitor is smaller than L when the length of the ceramic capacitor 100 in the longitudinal direction is L.

  In an actual printed wiring board, a ceramic resistor and a semiconductor chip are arranged near a ceramic capacitor. These elements may also function as vibration suppressing members. However, these functional parts are only disposed in the vicinity of the ceramic capacitor by chance for the design of the PCB 200, and are not intended to suppress noise. Does not include functional parts.

  FIG. 3A is a plan view showing a state in which the expansion / contraction suppression members 209a and 209b are arranged in the vicinity of both side surfaces in the longitudinal direction of the ceramic capacitor 100, and the PCB 200 is omitted. FIG. 3B also shows the PCB 200 in the side view of FIG. FIG. 3C is a plan view showing a state in which the expansion / contraction suppression members 211 a and 211 b are arranged in the vicinity of both side surfaces of the ceramic capacitor 100 in the short direction.

  When the ceramic capacitor 100 is mounted on the PCB 200, a strong vibration wave propagates in either the longitudinal direction or the short direction of the ceramic capacitor 100, and FIG. The arrangement shown in FIG. 3C can be selected. In FIG. 3A, vibration in the longitudinal direction of the ceramic capacitor 100 is suppressed, and in FIG. 3C, vibration in the short direction of the ceramic capacitor 100 is suppressed.

  When it is difficult to predict in advance in which direction a strong vibration wave propagates, there is a method of surrounding the ceramic capacitor 100 with an expansion / contraction suppression member 213 as shown in FIG. In the case of FIGS. 3A and 3C, the wiring pattern on the surface of the PCB 200 connected to the external terminals 101a and 101b of the ceramic capacitor 100 is not divided even if the expansion / contraction suppressing member is made of metal. can do. In the arrangement shown in FIG. 3D, when the expansion / contraction suppressing member 213 is formed of a metal, the through-holes are formed so that the wiring pattern on the surface of the PCB 200 connected to the external terminals 101a and 101b of the ceramic capacitor 100 is not divided. The vias are used to connect the conductive layers inside the PCB 200.

  FIG. 3E is a side view showing a state in which the expansion / contraction suppression members 215a and 215b are attached only to the back surface of the PCB 200. FIG. The expansion / contraction suppression members 215a and 215b are symmetrical with respect to the vibration suppression members 209a and 209b and the PCB 200 in FIG. In this case, when there is no wiring pattern on the rear surface, the mounting of the expansion / contraction suppressing member made of metal is facilitated. In addition, the space required for the functional element is not affected. Further, if the expansion / contraction suppression members 215a and 215b are arranged so as to fall within the range of projection of the ceramic capacitor 100 onto the PCB 200, the expansion / contraction movement at the position with the largest amplitude of the PCB 200 is performed as shown in FIG. Since it can be suppressed, it is effective.

  FIG. 3F is a plan view showing an arrangement state of the expansion / contraction suppressing members 217 a and 217 b with respect to the ceramic capacitor 100 arranged in the vicinity of the corner of the PCB 200. Since the end portion of the PCB 200 is normally fixed to the housing of the notebook PC, vibration can be suppressed also by the expansion / contraction suppression members 217a and 217b disposed on one side surface of the ceramic capacitor 100 in the longitudinal direction and the short side direction, respectively. In this case, the lengths of the expansion / contraction suppression members 217a and 217b may be increased so that the ceramic capacitor 100 is surrounded by the two pieces of the PCB 200 at the corner and the expansion / contraction suppression members 217a and 217b.

  FIG. 3G is a plan view showing a noise suppression structure for a capacitor group in which a plurality of ceramic capacitors 100 are aligned. The expansion / contraction suppression member 219 surrounds the entire capacitor group and is also disposed between the individual ceramic capacitors 100. FIG. 3H is a side view illustrating a state in which the expansion / contraction suppression members 221a, 221b, 221c, and 221d are fixed to the front surface and the back surface of the PCB 200. 3 (A) to 3 (G), the expansion / contraction suppression member is fixed only to one surface of the PCB 200. Therefore, the expansion / contraction suppression member is close to a rigid body to suppress vibration of the PCB 200. There was a need.

  When the PCB 200 vibrates, the stretching motion and the shrinking motion are simultaneously generated at the position of the front surface and the corresponding back surface. Therefore, by suppressing one of the motions, the vibration of the PCB is suppressed, and further noise is generated. Can be suppressed. As shown in FIG. 3 (H), if the expansion / contraction suppression members 221a, 221b, 221c, and 221d are fixed to the front and back surfaces so as to be plane-symmetric with respect to the PCB 200, only the compression or the tension is strong. The expansion / contraction suppression member can be formed of a material.

  Although the present invention has been described with the specific embodiments shown in the drawings, the present invention is not limited to the embodiments shown in the drawings, and is known so far as long as the effects of the present invention are achieved. It goes without saying that any configuration can be adopted.

  Can be used for printed circuit boards with ceramic capacitors.

It is a figure explaining the connection state of the DC-DC converter and decoupling capacitor which are mounted in a notebook computer. It is a figure which shows the attachment condition of a ceramic capacitor, and the mode of a vibration when a ceramic capacitor is surface-mounted on PCB. It is a figure explaining the structure which suppresses the noise resulting from a ceramic capacitor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Multilayer ceramic capacitor 200 ... Printed wiring board 209, 211, 213, 215, 217, 219, 221 ... Expansion / contraction suppression member

Claims (10)

A noise suppression structure for a printed wiring board,
A ceramic capacitor mounted on the surface of the printed wiring board;
A noise suppression structure having an expansion / contraction suppression member disposed around the ceramic capacitor and fixed to a surface of the printed wiring board.   The noise suppression structure according to claim 1, wherein the expansion / contraction suppression member is disposed in a range of a distance shorter than a length of the ceramic capacitor with respect to the ceramic capacitor.   3. The noise suppression structure according to claim 1, wherein the expansion / contraction suppression member is formed long and thin from metal or ceramics, and is disposed only on one surface of the printed wiring board.   The noise suppression structure according to any one of claims 1 to 3, wherein the expansion / contraction suppression member is disposed along a longitudinal direction and / or a lateral direction of the ceramic capacitor.   The noise suppression structure according to any one of claims 1 to 3, wherein the expansion / contraction suppression member is disposed so as to surround the ceramic capacitor.   The noise suppression structure according to any one of claims 1 to 3, wherein the expansion / contraction suppression member is disposed on a surface of the printed wiring board opposite to a mounting surface of the ceramic capacitor.   The noise suppression structure according to claim 6, wherein the expansion / contraction suppression member is disposed at a position including a projection of the ceramic capacitor with respect to the printed wiring board.   The noise suppression structure according to claim 1, wherein a plurality of the ceramic capacitors are arranged, and the expansion / contraction suppression member is disposed so as to surround each ceramic capacitor.   The noise suppression structure according to any one of claims 1 to 8, wherein the expansion / contraction suppression member is disposed on a front surface and a back surface of the printed wiring board. A printed wiring board;
A ceramic capacitor mounted on the surface of the printed wiring board;
An electronic device having an expansion / contraction suppressing member disposed around the ceramic capacitor and fixed to a surface of the printed wiring board.

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