JP2005026375A - Circuit board with shield, and acceleration sensor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit board with a shield which has such a structure that can be manufactured by an easier process and is smaller in size than the conventional one, and to provide an acceleration sensor using the same. <P>SOLUTION: The circuit board with a shield comprises a circuit board 1 on which electronic components are mounted, a shield case 2 which is so installed as to cover part of the circuit board 1 and the electronic component, and a ground layer 1a which is formed over the entire surface of at least part of the circuit board 1 covered by the shield case 2. The shield case 2 and the ground layer 1a are electrically connected to each other. Due to this structure, a space surrounded by the ground layer 1a and the shield case 2 is electromagnetically shielded and is not influenced by noise generated outside. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a shielded circuit board having a shield case for storing electronic components and an acceleration sensor using the same.
[0002]
[Prior art]
In general, in an acceleration sensor, a sensor chip (acceleration sensor chip) for detecting acceleration and a peripheral circuit including a sensor output amplification circuit for amplifying an output signal of the sensor chip are mounted on a single circuit board. The output signal of the sensor chip is very small compared to the signal input and output by the external circuit, and is easily affected by noise generated outside. Therefore, the circuit board on which the sensor chip and the peripheral circuit are mounted also serves as a shield. It is stored in a metal can (see, for example, Patent Document 1).
[0003]
As shown in FIG. 3, the can 2 ′ is formed in a plate-like base 2 a ′ through which leads 5 for connecting the circuit board 1 and an external circuit (not shown) are inserted and held, and a box-like opening on the lower surface. A cap 2b ′ having a space for housing the circuit board 1 between the base 2a ′ and a base 2a ′ is combined. The base 2a 'and the cap 2b' constitute a can 2 'by hermetically welding (hermetic sealing) the peripheral edge 2c' of the base 2a 'and the opening 2d' of the cap 2b '. In the can 2 ′, a holder 6 for holding the circuit board 1 is provided on the base 2a ′.
[0004]
[Patent Document 1]
JP 2001-208767 A (page 3, FIG. 1)
[0005]
[Problems to be solved by the invention]
However, in the can 2 ′ having the above-described configuration, since the base 2a ′ and the cap 2b ′ need to be hermetically welded when assembled, the manufacturing process is relatively complicated. Further, since the can 2 ′ is formed in a size that can accommodate the circuit board 1 therein, the size of the can 2 ′ is larger than that of the circuit board 1.
[0006]
The present invention has been made in view of the above-mentioned reasons, and of course, a shielded circuit board having a simpler manufacturing process and a smaller size compared to the conventional configuration, as well as shielding a necessary part, and a An object of the present invention is to provide an acceleration sensor used.
[0007]
[Means for Solving the Problems]
According to the first aspect of the present invention, a circuit board on which an electronic component is mounted, a shield case that covers the electronic component together with the circuit board, and is covered with at least a part of the circuit board, and at least the shield case is covered with the circuit board. And a grounding layer formed over the entire surface, and the shield case and the grounding layer are electrically connected.
[0008]
According to the present invention, since the space surrounded by the ground layer and the shield case is electromagnetically shielded as in the conventional configuration, the shield case is connected to the ground layer provided on the circuit board. Therefore, it is not necessary to perform the welding operation and the manufacturing process becomes simpler than the conventional configuration. Further, since the shield case is arranged on the circuit board, the size can be designed relatively freely, and the size can be reduced as compared with the conventional configuration.
[0009]
According to a second aspect of the present invention, there is provided an acceleration sensor using the shielded circuit board according to the first aspect, wherein the electronic component includes an acceleration sensor chip.
[0010]
According to the present invention, the acceleration sensor has a simpler manufacturing process and can be downsized as compared with the conventional configuration.
[0011]
According to a third aspect of the present invention, there is provided a feedthrough capacitor as a noise countermeasure component for preventing intrusion of noise into a portion surrounded by the shield case and the ground layer at the power input and output ends in the second aspect of the invention. Is added, and the noise countermeasure component is mounted in a portion different from the portion surrounded by the shield case and the ground layer in the circuit board.
[0012]
According to the present invention, the noise generated by the external circuit is blocked outside the portion surrounded by the shield case and the ground layer, and therefore does not affect the portion surrounded by the shield case and the ground layer.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0014]
As shown in FIG. 1, the shielded circuit board according to the present embodiment is an electronic component mounted on the circuit board 1 between the circuit board 1 and the circuit board 1, which is a multilayer circuit board having a ground layer 1 a as an inner layer. And a shield case 2 made of metal having a space for storing the battery. The shield case 2 is provided with a plurality of connection terminals 2a (four in the figure), and each connection terminal 2a is inserted and connected to a through hole 1b connected to the ground layer 1a in the circuit board 1, respectively. It is electrically connected to the ground layer 1a. With this configuration, noise generated outside the portion surrounded by the ground layer 1a and the shield case 2 is blocked by the ground layer 1a and the shield case 2 and is surrounded by the ground layer 1a and the shield case 2. It does not affect.
[0015]
In the present embodiment, the above-described shielded circuit board is used for an acceleration sensor including a sensor chip (acceleration sensor chip) for detecting acceleration, as will be described below. In the acceleration sensor, the signal output from the sensor chip 3 is smaller than a signal input / output by an external circuit (not shown) and is easily affected by noise generated outside, as shown in FIG. The sensor chip 3 is mounted on a portion of the circuit board 1 surrounded by the ground layer 1 a and the shield case 2. The peripheral circuit 4 inserted between the sensor chip 3 and the external circuit is also mounted on a portion surrounded by the ground layer 1 a and the shield case 2 in the same manner as the sensor chip 3. As shown in FIG. 2, the peripheral circuit 4 includes a sensor output amplifier circuit 4a that amplifies the output signal of the sensor chip 3, a sensor output adjustment circuit 4b that suppresses variations in the output signal due to the characteristics of the sensor chip 3, and And a sensor protection circuit 4c for protecting the acceleration sensor when the acceleration sensor is reversely connected to the external circuit or when an overvoltage is applied to the acceleration sensor from the external circuit.
[0016]
By the way, when the peripheral circuit 4 is connected to an external circuit, as shown in FIG. 1, one end portion is provided in the connection hole 1c provided in the circuit board 1 while avoiding a portion surrounded by the ground layer 1a and the shield case 2. A lead (not shown) to be inserted and connected is used. By connecting the other end of the lead to an external circuit, the connection hole 1c is connected to the external circuit. Further, a noise protection circuit for preventing noise from entering the peripheral circuit 4 is inserted between the connection hole 1 c and the peripheral circuit 4. In this embodiment, three connection holes 1c are provided for grounding, for power input supplied from an external circuit, and for output for outputting a signal to the external circuit. A feedthrough capacitor C1 as a noise countermeasure component is inserted between the circuit 4 and the noise protection circuit. Since the feedthrough capacitor C1 is mounted on the circuit board 1 while avoiding the portion surrounded by the ground layer 1a and the shield case 2, the noise in the signal supplied from the external circuit to the peripheral circuit 4 via the leads The portion of the substrate 1 surrounded by the ground layer 1a and the shield case 2 is not affected. A broken line A in FIG. 2 indicates a boundary between a portion surrounded by the ground layer 1a and the shield case 2 and other portions.
[0017]
【The invention's effect】
As described above, in the present invention, the space surrounded by the ground layer and the shield case is electromagnetically shielded as in the conventional configuration, and the shield case is connected to the ground layer provided on the circuit board. Therefore, the work of airtight welding is not required, and the manufacturing process becomes simpler than the conventional configuration. Further, since the shield case is disposed on the circuit board, the size can be set relatively freely, and the size can be reduced as compared with the conventional configuration.
[Brief description of the drawings]
FIG. 1 shows an embodiment of the present invention, wherein (a) is a top view and (b) is a side view.
FIG. 2 is a block diagram showing an acceleration sensor same as above.
3A and 3B show a conventional example, in which FIG. 3A is a top view, FIG. 3B is a side view, and FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Circuit board 1a Grounding layer 2 Shield case 3 (Acceleration) sensor chip C1 Feed-through capacitor

Claims (3)

A circuit board on which electronic components are mounted, a shield case that covers the electronic components together with the circuit board, and is covered over at least a part of the circuit board, and at least a portion of the circuit board that covers the shield case. A shielded circuit board, wherein the shield case and the ground layer are electrically connected. An acceleration sensor using a shielded circuit board, comprising the shielded circuit board according to claim 1, wherein the electronic component includes an acceleration sensor chip. Noise countermeasure parts for preventing intrusion of noise into a portion surrounded by the shield case and the ground layer are added to the power input and output terminals, and the noise countermeasure parts are connected to the shield case and the ground layer in the circuit board. The acceleration sensor using the shielded circuit board according to claim 2, wherein the acceleration sensor is mounted on a part different from the enclosed part.

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