GB2313962A

GB2313962A - Grounding of high-frequency electronic apparatus

Info

Publication number: GB2313962A
Application number: GB9710839A
Authority: GB
Inventors: Toshiharu Minobe; Hiroyuki Yanagida
Original assignee: Alps Electric Co Ltd
Current assignee: Alps Alpine Co Ltd
Priority date: 1996-06-05
Filing date: 1997-05-28
Publication date: 1997-12-10
Anticipated expiration: 2017-05-28
Also published as: JPH09326586A; CN1087898C; GB2313962B; GB9710839D0; CN1168618A

Abstract

In order to connect leads of an IC(5)and electrodes of a chip component (6) to be grounded, to a metal case (3) with a low impedance and to obtain a shield between electronic components, a metallic conductor (24) is provided at one surface of a printed circuit board. The metallic conductor is electrically connected to the metal case and is connected to the ground leads (9) of the electronic components (5,6) mounted on the front surface of the board. The metallic conductor may be either a metal plate having protrusions which project through holes in the board, or a coating of e.g copper foil, which is connected to the component leads via conductive pins. The ground plane may be shaped to provide a space for a further component attached to the same side of the board, e.g a coil (Fig.3, not shown).

Description

HIGH-FREOUENCY ELECTRONIC APPARATUS The present invention relates to high-frequency electronic apparatus. In particular, but not exclusively, it relates to high-frequency apparatus for TV tuners and VTR RF modulators.

In recent designs of high-frequency electronic apparatus, many so-called surface ..ounting-type electronic components are used to make the apparatus compact. The apparatus has a printed circuit board accommodated in a metal case. Wiring patterns are formed on one surface of the printed circuit board, and electronic components such as integrated circuits (ICs) and lead-less components (hereinafter called chip components) are soldered at specified positions on the patterns.

Figures 5 and 6 show such a conventional highfrequency electronic apparatus. Figure 5 is a plan illustrating a condition in which electronic components are mounted on a printed circuit board accommodated in a metal case. Figure 6 is a cross-section taken on line VI VI shown in Figure 5. In other words, as shown in Figures 5 and 6, wiring patterns 2 for connecting electronic components to each other and ground patterns 4 for connecting to a metal case 3 are formed on one surface (the upper surface) of a printed circuit board 1. A surface mounting-type IC 5 and chip components 6 are soldered at the specified positions on the wiring patterns 2 and the ground patterns 4 to form the high-frequency electronic circuit.

An assembly sequence is as follows: so-called solder paste is first applied to the specified positions on the wiring patterns 2 and the ground patterns 4 by the transfer method or by printing. Then, components such as the IC 5 and the chip components 6 are mounted and tentatively secured at the specified positions by an automatic mounting unit. Heating the printed circuit board in a reflow oven melts the solder paste for soldering to the printed circuit board 1. Leads 8 and 9 of the IC 5 and the electrodes 10 and 11 of the chip component 6 are connected to the wiring patterns 2 or the ground patterns 4. A lead 8 of the IC 5 and an electrode 10 of the chip component 6 are connected to the wiring patterns 2 which connect components. A lead 9 of the IC 5 and an electrode 11 of the chip component 6, which are a ground lead and a ground electrode grounding high frequencies to the metal case 3, respectively, are connected to the ground patterns 4. Then, the printed circuit board 1 is accommodated in the metal case 3, which has upper and lower openings, positioned by protrusions 12 formed on the metal case 3, and secured by soldering wide soldering sections 13 which are part of the ground patterns 4 and are formed on the periphery of the printed circuit board 1. In this way, a ground lead 9 of the IC 5, which grounds high frequencies, is connected to the metal case 3 through the ground patterns 4. The upper and lower openings are covered by covers 14 and 15 to complete the high-frequency electronic apparatus.

In a case when a part such as a coil 16 which requires avoidance of electromagnetic coupling with other components is used together with the surface mounting-type IC 5 and the chip components 6, a part having leads is used instead of lead-less chip components such that the part is disposed separately from other components to reduce electromagnetic coupling as much as possible. In other words, in the conventional apparatus, since the coil 16 is connected to a lead 8 of the IC 5 through the wiring pattern 2 but requires avoidance of electromagnetic coupling with the IC 5 and the chip component 6, a coil having leads is used as the coil 16 to increase the distances between the coil 16, and the IC 5 and the chip component 6 due to its height which is larger than those of the IC 5 and the chip component 6. Such a part having leads is manually soldered on the same surface as surfacemounting components are soldered, after surface-mounting components such as the IC 5 and the chip components 6 are soldered in the reflow oven.

Since such a conventional electronic apparatus is made compact, the wiring patterns 2 and the ground patterns 4 are very densely disposed. Because the IC 5, which has many leads such as leads 8 and 9, has a narrow lead pitch, the wiring patterns 2 and the ground pattern 4 are thin. Therefore, a ground lead 9 of the IC 5 to be connected to the metal case 3 for grounding and a ground electrode 11 of the chip component 6 must be connected to the metal case 3 with narrow ground patterns 4. As a result, a lead 9 of the IC 5 or the ground electrode 11 of the chip component 6 cannot be connected to the metal case 3 with sufficiently low impedance. The specified circuit performance may not be obtained or operation stability may deteriorate.

Since surface-mounting electronic components are used in the apparatus to make it compact, a so-called single-sided copper printed circuit board, which has copper foil for wiring on only one surface, is used as the printed circuit board 1. Because a part such as the coil 16, which requires avoidance of electromagnetic coupling with other components, is mounted on the same surface as other components, even if a part having leads is used to increase the distance between the part and the other components, electromagnetic coupling with the other components cannot be ignored. If a shielding plate (not shown) is used to completely eliminate electromagnetic coupling, putting it on the same surface as electronic components are mounted impairs the compactness of the apparatus. In addition, since patterns are densely drawn, putting the shielding plate on the surface is difficult in terms of structure.

The foregoing problems are solved in one aspect of the present invention through the provision of a highfrequency electronic apparatus including a metal case; a printed circuit board on which a surface mounting electronic component is mounted at one surface and which is accommodated in the metal case; a metallic conductor formed by a metal plate mechanically connected to the other surface of the printed circuit board and connected to the metal case, wherein the printed circuit board is provided with an island-shaped relay pattern connected to a ground lead or a ground electrode of the surface mounting electronic component at the surface on which the surface mounting electronic component is mounted, and the metal plate is connected to the island-shaped relay pattern in the vicinity of the ground lead or the ground electrode.

The foregoing problems are solved in a further aspect of the present invention through the provision of c high-frequency electronic apparatus including a metal case; a printed circuit board on which a surface mounting electronic component is mounted at one surface and which is accommodated in the metal case; plate-shaped metallic foil or a metal plate mechanically connected to the other surface of the printed circuit board and connected to the metal case; an electronic component having a lead mounted to the surface of the printed circuit board and connected to the surface mounting electronic component, wherein the plate-shaped metallic foil or the metal plate is extended so as to cover at least a portion where the electronic component having a lead is mounted.

The foregoing problems are solved in yet a further aspect of the present invention through the provision of a high-frequency electronic apparatus including a metal case; a printed circuit board on which surface mounting electronic component is mounted at one surface and which is accommodated in the metal case; a plate-shaped metallic conductor mechanically connected to the other surface of the printed circuit board and connected to the metal case; an electronic component having a lead mounted to the surface and connected to the surface mounting electronic component, wherein the printed circuit board is provided with a relay pattern connected to a ground lead of the surface mounting electronic component at the surface on which the surface mounting electronic component is mounted, and the plate-shaped metallic conductor is connected to the relay pattern in the vicinity of the ground lead and is extended so as to cover at least a portion where the electronic component having a lead is mounted.

Embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a plan of a high-frequency electronic apparatus according to a first embodiment of the present invention; Figure 2 is a cross-section taken on line Il-Il shown in Figure 1; Figure 3 is a perspective view of the highfrequency electronic apparatus according to the first embodiment or the present invention; Figure 4 is a cross-section of a high-frequency electronic component according to a second embodiment of the present invention; Figure 5 is a plan showing a condition in which electronic components are mounted on a printed circuit board accommodated in a metal case in a conventional highfrequency electronic apparatus; and Figure 6 is a vertical cross-section taken on line VI-VI shown in Figure 5.

Figures 1 to 3 show a high-frequency electronic apparatus according to a first embodiment of the present invention.

In these figures, on one surface (upper surface) of a printed circuit board 21, surface mounting type electronic components such as an IC 5 and chip components 6 are mounted, and their leads 8 and 9, and electrodes 10 and 11 are soldered to wiring patterns 22, a ground pattern 4, and relay patterns 23. The relay patterns 23 are used for relaying the ground leads 9 and the ground electrode 11 which are to be connected to a metal case 3, among the leads 8 and 9 and the electrodes 10 and 11. The relay patterns 23 are connected to the ground leads 9 and the ground electrodes 11 and are formed in island shapes.

Among the ground leads 9 and the ground electrode 11, terminals relatively distant from the metal case 3 are soldered to the relay patterns 23 and terminals relatively close to the metal case 3 are soldered to the ground pattern 4. The lead 8 and the electrode 10 are soldered to wiring patterns 22 such as a pattern which connects between chip components 6 or which connects a chip component 6 and the IC 5.

On the other hand, as shown in Figure 3, a plate-shaped metallic conductor, a metal plate 24 such as an iron plate in this embodiment, for example, is mechanically connected to almost the entire area of the other surface (lower surface) of the printed circuit board 21. The metallic conductor formed by the metal plate 24 may be just put on the printed circuit board.

Alternatively, it may be adhered to the printed circuit board. It is desirable that the thickness of the metal plate 24 be more than 0.1 mm. The metal plate 24 is provided with protruding pieces 25 formed close to the ground leads 9 of the IC 5 and the ground electrode 11 of the chip component 6 both of which are disposed relatively distant from the metal case 3. The protruding pieces 25 pass through holes 26 on the printed circuit board 21 to the upper surface and are soldered to the relay patterns 23 on the upper surface. The metal plate 24 is soldered to the metal case 3 at a plurality of portions on the periphery of the plate. Also in this embodiment, the printed circuit board 21 is positioned in the metal case 3 by protrusions 12 formed on the metal case 3, together with the metal plate 24 as shown in Figure 3.

A coil 27 is mounted on the lower surface of the printed circuit board 21. A lead 28 of the coil 27 passes through a hole 29 made in the printed circuit board 21 and is soldered to the wiring pattern 22 on the upper surface to connect to a lead 8 of the IC 5. The metal plate 24 is provided with a hollowed-out section 30 at an area where the coil 27 is mounted, in order to avoid mutual contact.

The metal plate 24 needs to cover, around the area where the coil 27 is mounted, at least an area where the other electronic components are mounted to avoid electromagnetic coupling. The metal plate 24 does not necessarily cover the entire area of the lower surface of the printed circuit board 21. It is desirable that the protruding pieces 25 of the metal plate 24 be provided close to the ground leads 9 of the IC 5 or the ground electrode 11 of the chip component 6 which is to be connected to the metal case 3, and be connected to the relay patterns 23. By providing the relay patterns 23 in this way, the ground leads 9 can be connected to the metal plate 24 with a shorter length than that to the metal case 3.

With the above-described structure, the ground leads 9 of the IC 5 and other terminals to be connected to the metal case 3 are connected to the wide metal plate 24 by use of the relay patterns 23 over the shortest distance. Since the metal plate 24 is connected to the metal case 3 at a plurality of portions, a current flowing through the metal plate 24 is divided and the metal plate 24 is grounded to the metal case 3 with a very low impedance. Therefore, the metal plate 24 achieves the same grounding effect as the metal case 3. Since the coil 27 is mounted on the lower surface of the printed circuit board 21 and the metal plate 24 covers around the coil 27, even if the coil 27 generates magnetic flux, the flux is shielded by the metal plate 24 and does not electromagnetically couple with the components mounted on the other surface of the printed circuit board.

In the first embodiment, the metal plate 24 is mechanically connected to almost the entire area of the lower surface of the printed circuit board 21. The shape of the metal plate 24 is not limited to this case. It may be a wide belt-shaped metal plate covering an area including the protruding pieces 25 to the metal case 3.

In the first embodiment, as a plate-shaped metallic conductor, the metal plate 24, which is independent from the printed circuit board 21, is used.

The structure of the metal plate 24 is not limited to this case. In a second embodiment, as shown in Figure 4, a socalled double-sided copper board 31 may be used, for example, and the same advantages can be obtained. In this case, copper foil 32 which is at the lower surface of the double-sided copper board 31 is used as a substitute for the metal plate 24, and pin-shaped conductive leads 33 passing through holes 26 made on the printed circuit board are used to connect the copper foil 32 to the relay patterns 23. Instead of the conductive leads 33, electrically conductive plating may be applied to the inner walls of the holes 26. Since the number of components used is reduced with the use of the doublesided copper board 31, assembly work is facilitated as compared with a case in which the metal plate 24 is used.

As described above, according to the present invention, since the metal plate is mechanically connected to the lower surface of the printed circuit board, the metal plate is connected at short distances to the ground leads of electronic components mounted on the upper surface of the printed circuit board, and the metal plate is soldered to the metal case, the ground leads of the electronic components are grounded to the metal case at low impedances and the circuit performance is increased and stabilised. Since the leads are grounded to the metal case through the metal plate at the lower surface, there is no need to provide a wide ground pattern on the upper surface and the apparatus can be made more compact.

Since an electronic part which avoids electromagnetic coupling with the other electronic components is mounted on the surface opposite the surface on which the other components are mounted and an area around the electronic part is covered by the plate-shaped metallic foil or the metal plate mechanically connected to the printed circuit board, the electronic part is shielded by this metallic foil or the metal plate. In this case, as the plate-shaped metallic foil, the copper foil at the lower surface of the printed circuit board having copper foil adhered to both surfaces may be used.

In addition, since the plate-shaped metallic conductor is connected to the ground leads of electronic components and the concuctor covers an area around an electronic part which avoids electromagnetic coupling, satisfactory grounding and shielding can be obtained at the same time. Also in this case, as the metallic conductor, either a metal plate independent from the printed circuit board or the copper foil adhered to the lower surface of the printed circuit board may be used.

Claims

1. A high-frequency electronic apparatus comprising: a metal case; a printed circuit board on which a surface mounting electronic component is mounted at one surface and which is accommodated in said metal case; a metallic conductor formed by a metal plate mechanically connected to the other surface of said printed circuit board and connected to said metal case, wherein said printed circuit board is provided with a relay pattern connected to a ground lead or a ground electrode of said surface mounting electronic component at the surface on which said surface mounting electronic component is mounted, and said metallic conductor formed by said metal plate is connected to said relay pattern in the vicinity of said ground lead or said ground electrode.

2. A high-frequency electronic apparatus comprising: a metal case; a printed circuit board on which a surface mounting electronic component is mounted at one surface and which is accommodated in said metal case; plate-shaped metallic foil or a metal plate mechanically connected to the other surface of said printed circuit board and connected to said metal case; an electronic component having a lead mounted to the other surface of said printed circuit board and connected to said surface mounting electronic component, wherein said plate-shaped metallic foil or said metal plate is extended so as to enclose at least a portion where said electronic component having a lead is mounted.

3. A high-frequency electronic apparatus comprising: a metal case; a printed circuit board on which a surface mounting electronic component is mounted at one surface and which is accommodated in said metal case; a plate-shaped metallic conductor mechanically connected to the other surface of said printed circuit board and connected to said metal case; an electronic component having a lead mounted to the other surface of said printed circuit board and connected to said surface mounting electronic component, wherein said printed circuit board is provided with a relay pattern connected to a ground lead or a ground electrode of said surface mounting electronic component at the surface on which said surface mounting electronic component is mounted, and said plateshaped metallic conductor is connected to said relay pattern in the vicinity of said ground lead or said ground electrode and is extended so as to enclose at least a portion where said electronic component having a lead is mounted.

4. A high-frequency electronic apparatus according to Claim 3, wherein said plate-shaped metallic conductor is copper foil adhered to said printed circuit board.

5. A high-frequency electronic apparatus according to Claim 3, wherein said plate-shaped metallic conductor is a metal plate.

6. A high-frequency electronic apparatus according to Claim 5, wherein said metal plate is provided with a protruding piece passing through said printed circuit board and said protruding piece is connected to said relay pattern.

7. A high-frequency electronic apparatus substantially as hereinbefore described with reference to, and as illustrated by, any of Figures 1 to 4 of the accompanying drawings.