JPH08204377A - Shielding body - Google Patents

Abstract

PURPOSE: To prevent high-frequency noises from mingling with a digital/analog board. CONSTITUTION: An integrated circuit 5 is covered with a shielding body 1 and mounted on a board 10 so that the integrated circuit 5 is isolated from the other circuits. At the same time, radiation noises can be absorbed by inner wave-absorbing ferrite 24. An outer electrode 21, a dielectric ceramic member 23, and an inner electrode 22 constitute a capacitor. The inner electrode 2 and the outer electrode 23 have each connected lead 3 or 4. In addition, these leads 3 and 4 are connected to a power supply pin 8 or a grounding pin 7 in the integrated circuit 5 to activate the capacitor, while noises at a power-supply pattern are carried to the ground.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shield, and more particularly to an EMC of a circuit in which a digital circuit and an analog circuit are mixed.
(Electromagnetic compatibility) The present invention relates to a shield that is effective in reducing obstacles.

[0002]

2. Description of the Related Art As is well known, a PLL circuit is composed of a mixed circuit of a digital circuit that handles digital signals and an analog circuit that handles analog signals. Conventionally, electromagnetic shielding of such a mixed circuit is performed as shown in FIG.

The PLL circuit has a digital circuit section 32. The digital circuit section 32 is shielded by a shield 31 made of a metal plate so that noise generated from the digital circuit section 32 does not affect other circuits mounted on the same substrate. Further, by inserting a plurality of feedthrough capacitors 33 into a plurality of through holes provided in the shield 31 and soldering them, a high frequency noise component generated from the digital circuit section 32 is passed through the plurality of feedthrough capacitors 33. Let it escape to the shield 31. With such a structure, noise generated in the digital circuit section 32 is prevented from mixing into other circuits through the plurality of patterns 36. Shield 3
1 is attached to a substrate 38 with screws 37. The plurality of patterns 36 and the plurality of feedthrough capacitors 33 are connected to a plurality of terminals 34 standing on a substrate 38 and a plurality of wires 35, respectively.

Here, as a prior art, for example, Japanese Patent Laid-Open No.
JP-A-26082 uses a sub-shield plate in which a conductive member is laminated on a dielectric plate in which a plurality of through holes through which a plurality of conductors pass is formed in order to shield between an analog circuit and a digital circuit. The technology is disclosed.

[0005]

As described above, in the conventional shield body, as shown in FIG. 3, the shield body 31 is attached to the substrate 38 with the screw 37, and the feedthrough capacitor 33 penetrates the shield body 31. Soldered in the hole. In such a configuration, it takes a lot of time and effort to mount the shield 31 on the substrate 38, so that there is a problem that work efficiency is not good. Further, since a capacitor 33 is individually required to shield high frequency noise, the mounting space of the capacitor 33 and the work efficiency at the time of mounting become a problem. Furthermore, in the conventional shield, only noise countermeasures are taken so that the electromagnetic waves radiated from the noise source inside the shield are not leaked to the outside of the shield, which is effective as a noise countermeasure to the outside of the shield. However, no consideration is given to the influence on the circuit inside the shield.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a shield which is capable of preventing high-frequency noise from being mixed in a mixed digital / analog circuit board and which can be easily mounted. .

Here, the above-mentioned prior art discloses a technique in which a conducting wire and a conductive member form a feedthrough capacitor via a dielectric plate to efficiently shield high frequency noise. There is a drawback that it is difficult to manufacture the sub-shield plate because it is necessary to form as many through-holes as there are conducting wires.

[0008]

In order to achieve the above object, a shield according to the present invention is generated from a digital circuit when a circuit in which a digital circuit and an analog circuit are mixed is mounted on the same substrate. In a shield that shields noise from affecting the analog circuit,
It has a laminated structure including a box-shaped dielectric material having an opening on one side, an inner electrode formed inside the dielectric material, and an outer electrode formed outside the dielectric material. And a radio wave absorber on the inner surface of the inner electrode.

[0009]

In the shield according to the present invention, the layer forming the shield has a laminated structure of electrode-dielectric-electrode, and the shield itself has a function as a capacitor.

The capacitance C of the capacitor is expressed as C = ε ₀ · ε _s · A / d [F / m]. Here, ε ₀ is the dielectric constant of vacuum (= 8.85).
5 × 10 ⁻¹² ), ε _s is the relative permittivity of the dielectric, A is the counter electrode area of the electrode, and d is the distance between the electrodes. Capacitance C of capacitor
Should set the above-mentioned ε _s , A, and d appropriately.

A radio wave absorber is provided on the inner surface of the shield. A lead wire is connected to each of the two electrodes, and the shield may be mounted by inserting the lead wire into a through hose of the substrate and soldering the lead wire.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 2 is a mounting view of a shield according to an embodiment of the present invention. FIG. 1 is a cross-sectional view when the shield 1 is mounted on the printed board 10. An integrated circuit 5 which is a digital circuit is mounted on a printed circuit board 10. Shield 1
Is formed by pressing the dielectric ceramics 23 into a shield shape (box shape) and applying conductive paint on both surfaces thereof to form the outer electrode 21 and the inner electrode 22. It is created by applying ferrite 24. In this embodiment, the outer electrode 21
Insulating film paint 30 is applied to.

The inner electrode 22 and the outer electrode 2 of the shield 1
Lead wires 3 and 4 are connected to 1 respectively. Also, through holes 11 and 12 are formed in the printed circuit board 10 at positions corresponding to the lead wires 3 and 4, respectively. In order to electromagnetically shield the integrated circuit 5 from other external circuits such as analog circuits, the shield 1 is covered with the integrated circuit 5, and the lead wires 3 and 4 are provided in the through holes 11, respectively.
Printed circuit board 1
The shield 1 is mounted on 0. The integrated circuit 5 has a ground pin 7 and a power supply pin 8 in addition to the plurality of electrode pins 6. A plurality of signal patterns 9 are formed on the surface of the printed board 10, and the electrode pins 6 are connected to one ends of the signal patterns 9.

A power supply print pattern 25 and a ground print pattern 26 are formed on the back surface of the printed circuit board 10. The lead wire 3 is electrically connected to the power supply pin 8 of the integrated circuit 5 via the power supply print pattern 25.
Similarly, the lead wire 4 is also connected to the ground pin 7 of the integrated circuit 5 via the ground print pattern 26.

The printed circuit board 10 has a pattern 27 on one surface of the power source.
And a ground surface pattern 28 are formed. A closed space is formed by the inner electrode 22 of the shield 1 and the power supply one-side pattern 27 or the ground one-side pattern 28.

By mounting the shield 1 as described above,
Noise radiated from the integrated circuit 5 in the closed space can be absorbed by the radio wave absorber ferrite 24 on the surface of the inner electrode 22 and electromagnetically shielded in the same substrate as the external circuit of the shield 1. .

Since the capacitor is formed by the outer electrode 21, the dielectric ceramics 23, and the inner electrode 22, the lead wires 3 and 4 are electrically connected to the power supply pin 8 and the ground pin 7 of the integrated circuit 5, respectively. The capacitor can be used as a bypass capacitor that works extremely effectively at high frequencies. By using the above capacitor as a bypass capacitor, not only electromagnetic field shielding from an external circuit but also noise radiation to the power supply pattern can be released to the ground.

It is needless to say that the present invention is not limited to the above-mentioned embodiments, and that various modifications may be made without departing from the scope of the present invention.

[0020]

As described above, in the shield according to the present invention, since the shield itself has a function as a bypass capacitor, a feedthrough capacitor individually connected to an integrated circuit is not necessary, and the shield inside and outside the shield is not required. Radiation of high frequency noise to both circuits can be prevented. Further, since the lead wire of the shield is inserted into the through hole of the substrate and soldering is performed, the work efficiency is improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a state where a shield according to an embodiment of the present invention is mounted on a substrate together with an integrated circuit.

FIG. 2 is a perspective view showing a state in which the shield shown in FIG. 1 is mounted on a substrate.

FIG. 3 is a partially transparent perspective view showing a conventional shield mounted on a substrate.

[Explanation of symbols]

 1 Shield 3,4 Lead Wire 5 Integrated Circuit 6 Electrode Pin 7 Ground Pin 8 Power Pin 9 Signal Pattern 10 Printed Circuit Board 11, 12 Through Hole 21 Outer Electrode 22 Inner Electrode 23 Dielectric Ceramic 24 Radio Wave Absorber Ferrite 25 Power Print Pattern 26 Ground Print Pattern 27 Power Supply One Side Pattern 28 Ground One Side Pattern 29 Solder 30 Insulating Film Paint

Claims (2)

[Claims] 1. A shield that shields noise generated from the digital circuit so as not to affect the analog circuit when a circuit in which a digital circuit and an analog circuit are mixed is mounted on the same substrate. A box-shaped dielectric having an opening, an inner electrode formed inside the dielectric, and an outer electrode formed outside the dielectric, and having a laminated structure, the inner electrode and the outer electrode A shield having a function of accumulating electric charges between the inner electrode and a radio wave absorber on the inner surface of the inner electrode. 2. A power supply print pattern and a ground print pattern are formed on the back surface of the substrate, and first and second through holes reaching the power supply print pattern and the ground print pattern are formed on the substrate, respectively. The shield is provided with a first lead wire having one end connected to the inner electrode and inserted into the first through hole, and a shield wire having one end connected to the outer electrode and the second through hole. The shield according to claim 1, having a second lead wire inserted therein.