KR20000005418A - Electromagnetic shield for a radiotelephone - Google Patents

Abstract

PURPOSE: Disclosed is an electromagnetic shield incorporated into a radiotelephone and having a series of spaced apart spring contacts that extend from the side wall for electrical contact with a ground trace on a printed circuit board. CONSTITUTION: The radiotelephone (30) includes a printed circuit board (48) having a ground trace (50) extending around an electrical circuit formed on the printed circuit board (48). The electromagnetic shield (10) is disposed adjacent the printed circuit board (48) for isolating the electrical circuit thereon. Forming a part of the electromagnetic shield (10) is a face, a side wall (14), and a series of spaced apart spring contacts (16) that extend from the side wall (14) for electrical contact with the ground trace on the printed circuit board (48). Disposed over the shield (10) is a housing structure that engages the shield and urges the shield against the printed circuit board (48) such that the spring contacts (16) thereof engage and make electrical contact with the ground trace of the printed circuit board.

Description

Electromagnetic Shield for Cordless Phone

Electromagnetic interference is a well known general problem with electronic equipment. Normal circuit operation will lead to undesirable signals and generate electromagnetic waves that interfere with the normal operation of other electronic components. Such undesirable signals, referred to as electromagnetic or radio frequency (RF) interference, can be minimized by shielding portions of circuitry within the conductive shield with low or ground potential. Such grounded electromagnetic shielding shields the circuit from electromagnetic interference by dissipating electrostatic accumulation and absorbing electromagnetic fields.

The same concerns about electromagnetic interference are provided in the design of cordless telephones. Shielding from electromagnetic interference is fundamental to maintaining optimal circuit performance and clear talk. Analog circuits are typically very sensitive to electromagnetic interference and must be shielded to ensure proper operation. Although not sensitive to electromagnetic interference, digital components generate high-frequency square waves that cause vast electromagnetic interference. Since current cellular radiotelephones use both analog and digital components, shielding electrical components from electromagnetic contamination is essential for clean communication between base stations and terminals.

In the past, it has been common to solder electromagnetic shields to ground traces formed on printed circuit boards of cordless telephones. This approach provided excellent conductive contact between the ground trace of the printed circuit board and the shield. However, soldering the electromagnetic shield to the printed circuit board makes it virtually impossible to inspect and repair the printed circuit board. It is highly desirable that the shield and the printed circuit board have a design that is easy to inspect and repair.

The conductive gasket can be used as a conductive interface between the printed circuit board and the electromagnetic shield of the radiotelephone. However, these also have drawbacks. In particular, conductive gaskets are very expensive and cannot compensate for warpage of a printed circuit board beyond the thickness of the gasket.

Spring clips and fingers are used in cordless telephones to maintain conductive contact between the ground traces formed on the printed circuit board and the electromagnetic shield. For example, US Patent No. 5.053.924 and Japanese Patent No. 6-112680 describe such matters. However, these spring clip and finger designs do not successfully approach the problem of bending the printed circuit board itself. Printed circuit boards have a potential for bending, and in fact, spring clips and fingers of conventional designs are so curved that they cannot maintain electrical contact around the entire printed circuit board. The spring clip or finger is quite rigid and is not designed to bend and move up and down between the printed circuit board and the electromagnetic shield to compensate for bending.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiotelephone, and more particularly to an electromagnetic shield for shielding a printed circuit board in a radiotelephone.

1 is a perspective view of an electromagnetic shield of the present invention.

2 is a partially enlarged perspective view of an electromagnetic shield showing a spring contact;

3 is a partial cross-sectional view of an electromagnetic shield of another design.

4 is a partial side view of another design of FIG.

5 is a partial cross-sectional view of an electromagnetic shield with another design according to the invention.

Figure 6 is a partial cross sectional view of an electromagnetic shield with another design according to the present invention.

7 is an enlarged view of a radiotelephone in which the electromagnetic shielding portion of the present invention is used.

8 is a partial side view of a radiotelephone in which the housing is partially cut away to show how the rear housing pressurizes the electromagnetic shield to contact the printed circuit board.

9 is a partial cross-sectional view of a wireless telephone.

The present invention relates to an electromagnetic shield for a wireless telephone. The radiotelephone includes a printed circuit board having an electrical circuit and a ground trace formed on the circuit. The electromagnetic shield is disposed adjacent to the printed circuit board to insulate the electrical circuit. The electromagnetic shield includes a surface and sidewalls extending from the surface. A series of spaced spring contacts extend from the side wall of the shield and are in electrical contact with the ground trace of the printed circuit board. The housing structure is disposed adjacent to the shield to engage the shield, and presses the spring contacts to engage with a ground trace extending around the printed circuit board.

It is an object of the present invention to provide an electromagnetic shield having a plurality of spring contacts for coupling with a conductive strip formed on a printed circuit board that allows a significant amount of spring contact compression while maintaining good electrical contact with the ground trace of the printed circuit board. will be.

Another object of the present invention is to maintain the electrical load to ensure electrical contact with the printed circuit board due to the inherent "spring back" nature of the finger contact, while the spring contacts can be deformed during assembly and thus required for the assembly of the shield It is to provide an electromagnetic shield having the above-described features that can lower the overall force.

It is a further object of the present invention to provide an electromagnetic shield for a radiotelephone which provides good electrical contact between adjacent printed circuit boards and the shield and in which the shield can be easily removed from the printed circuit board for inspection and repair.

Another object of the present invention is to provide an electromagnetic shield having a spring contact that compensates for gaps and normal curvatures within 1 mm in a printed circuit board.

Other objects, features and advantages of the present invention will be more clearly understood by the following detailed description with reference to the accompanying drawings.

1 and 2 show the electromagnetic shield 10 of the present invention. The shield 10 includes a surface 12 and a peripheral side wall 10. A series of spaced spring contacts 16 extending around the outer periphery of the shield extends from the side wall 14. Each spring contact 16 includes a finger tab or first tab 16a and a flexible finger 16b (FIG. 2).

The tabs 16a are selectively cut from the sidewall 14 and folded outward along the fold line so that they generally project in a plane extending perpendicular to the plane of the sidewall 14. Finger 16b is formed by a second set of fold lines extending between finger tab 16a and finger 16b. The finger 16b is bent up and down with respect to the surface 12 of the electromagnetic shield 10.

The second tab 24 is disposed adjacent each finger or first tab 16a. The tab 24 is disposed between the series of spring contacts 16 and extends outward from the sidewall 14 parallel to the finger tab 16a forming part of the spring contacts. Thus, as shown in FIGS. 1 and 2, the tab 24 is disposed between the series of spring contacts 16. Thus, the tabs 16a, 24 form a set of tabs or pairs of tabs around the outer periphery of the sidewalls. The tabs 16a, 24 are also interconnected by connecting segments 18, which form part of the sidewalls 14. In general, the tab 24 is consistent with the design of the tab 16a except that it does not include a suspension finger 16b.

The tabs 16a, 24 include an upper edge 26 that projects outward from the sidewall 14. As mentioned above, the upper edges 26 of the tabs 16a, 24 cooperate with each other to form a bearing surface. In particular, the upper edges 26 of the tabs 16a, 24 are joined by a second bearing surface (like a flange of the housing), which presses the entire shielding portion 10 into contact with the printed circuit board. . Thus, the upper edges 26 of the tabs 16a, 24 perform a common action that acts as a bearing surface.

A series of cutouts 22 are arranged around the circumference of the shield 10. The notch 22 causes a screw sleeve or the like to protrude through the shield 10 when the shield is assembled into the housing structure.

The spring contact 16 extending from the sidewall 14 is flexible and is designed to move up and down in a plane perpendicular to the surface 12 of the shield 10. Thus, the spring contacts 16 coincide with irregular or uneven surfaces, such as curved printed circuit boards, and maintain good electrical contact with conductive strips or ground traces formed on the printed circuit board.

In the embodiment shown in FIGS. 1 and 2, the spring contact 16 is arranged outside the side wall 14 of the shield. However, the spring contact 16 can rotate in and out relative to the side wall 14. In practice, the spring contact 16 can be cut and folded such that the finger 16b is aligned with the sidewall 14.

3 to 6 show three embodiments of the electromagnetic shield 10. In two of the three embodiments, the spring contact 16 comprises a triangular tab 16a cut from the side wall 14 and a finger 16b extending from the tab. The printed circuit board 48 having the ground trace 50 is disposed adjacent to the shield 10. In the embodiment of FIGS. 3 and 4, the spring contact 16 rotates outward from the side wall 14. 5 shows the same design but the spring contact 16 is rotated inward. In another embodiment of FIG. 6, the spring contact 16 is formed such that the finger 16b is aligned or centered with the sidewall 14. In the above three different embodiments, the upper edge angle of the tab 16a is not particularly suitable in part to act as a bearing surface, which is the upper edge 26 of the tabs 16a, 24 shown in FIGS. 1 and 2. . Thus, in the embodiments of FIGS. 3-6, the surface 10 or portions thereof may be coupled to press the electromagnetic shield 10 to an adjacent printed circuit board.

The shield 10 is formed by a series of die cutting operations. Thus, the shield comprising the surface 12 and the sidewalls 14 and the spring contacts 16 forms an integral integrated structure. Various conductive materials may be used to construct the electromagnetic shield 10. One such material for the shield 10 is beryllium-copper. The beryllium-copper includes excellent conductive properties and imparts good "spring-back" properties to the spring contacts 16.

In FIG. 7, the electromagnetic shield 10 of the present invention is shown as used in a conventional cellular radiotelephone 30. As shown in FIG. The radiotelephone 30 includes four basic parts, a front housing 32, a printed circuit board 48, an electromagnetic shield 10, and a rear housing 36. Details of the radiotelephone 30 are not claimed by the present invention and cellular radiotelephones are well known in the art and are in wide use and will not be described. For example, the radiotelephone 30 may be one of many radiotelephones manufactured by Ericsson Incorporated, North Carolina Research Triangle Park, such as the Ericsson AH-320.

As shown in FIGS. 7 to 9, the printed circuit board 48 and the shield 10 are sandwiched between the front housing 32 and the rear housing 36. The ground traces or conductive strips 50 extend around many electrical components 58 secured to the printed circuit board 48 facing the shield 10.

The front housing 32 has a conventional design and includes a flip cover 34 to protect the keyboard in a closed state. 8 schematically shows a part of the keyboard. The keyboard rests on the printed circuit board 48 and includes a series of pushbuttons 60 operative to actuate the lower pill 62.

The rear housing 36 includes a rear 38, a side wall 40, and an inner cavity 42. A series of spaced apart screw sleeves 44 is arranged around the outer periphery of the rear housing 36. The screw sleeve 44 is aligned with and protrudes through each cutout 22 formed in the adjacent shield 10.

The outer flange 54 is formed around the outer circumference of the rear housing 36. The outer flange 54 contacts the surrounding edge of the front housing 32 (FIG. 9). The inner flange 56 extending around the outer circumferential portion of the rear housing 36 is concave inward from the outer flange 54. The inner flange 56 is engaged with the upper edge 26 of the tabs 16a, 24 forming part of the shield 10 as shown in FIGS. 1 and 2. In practice, the inner flange 56 is engaged with the upper edge 26 and pressurizes the spring contacts 16 to make electrical contact with the ground trace 50 extending around the printed circuit board 48. In assembly, as shown in FIGS. 8 and 9, the shield 10 is seated in a cavity 42 formed in the rear housing 36. A screw (not shown) extends through the screw sleeve and connects the rear housing 36 to the front housing 32. The printed circuit board 48 is sandwiched between the front housing 32 and the shield 10. When the radiotelephone 30 is assembled, the rear housing 36 presses the spring contacts 16 and the shield 10 toward the printed circuit board 48, so that the fingers 16b are moved to the printed circuit board 48. 8 and 9 are coupled with a ground trace 50 extending around. Thus, a continuous non-uniform force is applied about the entirety of the shield 10 through the tabs 16a and 24 by the inner flange 56 of the rear housing 36.

As shown in FIG. 8, a series of openings 52 are formed around the outer circumference of the shield 10. Each opening 52 is generally bounded by a finger 16b, tabs 16a and 24, a terminal edge of the sidewall 14, and a printed circuit board 48. The size of the opening 52 should be limited so that its maximum dimension does not exceed 1/10 of the frequency wavelength to be shielded. In conventional applications involving cordless telephones, the longest opening 52 dimension does not exceed 3-6 mm.

In some cases, it may be desirable to provide additional contacts to ground the components of the radiotelephone 30. For example, in FIG. 7, the shield 10 has a spring contact 20 protruding outward from the side wall 14. The spring contacts 20 are cut out to protrude outward for electrical contact with adjacent structures such as antenna connectors and speaker connectors and then folded outwardly from the sidewalls 14.

The shield 10 of the present invention has various advantages over the conventional electromagnetic shield designed to be soldered to a printed circuit board. The shield 10 should be designed to maintain good electrical contact with the ground trace 50 of the printed circuit board 48 in a copper strip that is easily and quickly removed for inspection and repair of the printed circuit board. In addition, the spring contact 16 of the shield must be able to withstand actual pressure without degrading the performance of the finger 16b in order to maintain good electrical contact with the adjacent ground trace 50. The vertical durability that can be absorbed by the spring contacts 16 generally depends on the yield strength or elastic limit of the shield material. The shield design of the present invention, although a large amount of deformation may occur at the spring contact 16, there is some spring-back characteristic at the spring contact 16 when the load is released and the ground trace of the printed circuit board 48 It is unique in that it ensures electrical contact between 50 and the shield.

Finally, printed circuit boards tend to bend. The flexibility of the spring contacts 16 and the ability to bend upward or downward relative to the surface 12 of the shield is supported even when the printed circuit board has a normal bend of up to 1 mm.

The present invention has been described with reference to the preferred embodiments, and is not limited thereto, and one of ordinary skill in the art should recognize that various modifications and changes can be made to the present invention without departing from the appended claims.

Claims (46)

An electromagnetic shield for shielding an electrical circuit disposed on a circuit board having a conductive strip extending around the electrical circuit, the electromagnetic shield comprising: Surface, Sidewalls extending around at least a portion of the surface, Formed integrally with the sidewalls and comprising a series of spring contacts extending therefrom for electrical contact with a conductive strip extending around the circuit board, And the spring contact is flexible and movable up and down relative to the surface of the shield. 2. The electromagnetic shield of claim 1, wherein the spring contact is bent around a fold line spaced from the terminal end of the spring contact. 2. The spring contact of claim 1 wherein each spring contact comprises a first tab protruding from a plane of the side wall and a finger extending from the first tab and bending around a fold extending between the first tab and the finger. Electromagnetic shielding part. 4. The shield of claim 3, wherein a shield is installed between the printed circuit board and the housing, each first tab including an upper edge coupled by the housing and protruding outward from the sidewalls such that the spring contact is coupled with the conductive strip. Electromagnetic shielding part characterized in that the pressing toward the printed circuit board. 5. The shield of claim 4, wherein the shield includes a second tab group disposed between each spring contact and projecting outwardly from the sidewall, the second tab including an upper edge coupled by the housing. Electromagnetic shielding. 2. The electromagnetic shield of claim 1, wherein the spring contacts protrude into the sidewalls. The electromagnetic shield of claim 1, wherein the spring contacts are aligned with the sidewalls. 2. The electromagnetic shield of claim 1, wherein the spring contacts protrude out of the sidewalls. An electromagnetic shield for shielding an electrical circuit disposed on a circuit board having a conductive strip extending around the electrical circuit, the electromagnetic shield comprising: Surface, Sidewalls extending around at least a portion of the surface, A series of spaced spring contacts extending from said sidewall, Each spring contact includes a first tab protruding from the sidewall and a finger integrally formed with and extending from the first tab for electrical contact with a conductive strip formed on a printed circuit board, the spring contacting the surface and the sidewall; The shield with spring contacts constitutes an integral structure formed of a conductive material. 10. The electromagnetic shield of claim 9, wherein the shield is installed between the printed circuit board and the housing, and the first tab protrudes outward from the side wall. 11. The electromagnetic shield of claim 10, wherein the shield includes an upper edge coupled by the housing, thereby forcing the shield against the printed circuit board that is coupled with a conductive strip having spring contacts formed on the printed circuit board. part. 10. The electromagnetic shield of claim 9, wherein the shield includes a second tab group that protrudes outward from the sidewalls, the second tab being disposed between each first tab. 13. The electromagnetic shield of claim 12, wherein the first and second tabs protrude outward from the plane of the sidewalls to form a series of tab sets. 14. The electromagnetic shield of claim 13, wherein each set of tabs are interconnected by sidewall segments. 14. The electromagnetic shield of claim 13, wherein each set of tabs includes an upper edge protruding outward from the sidewalls, and the shield is pressed toward the printed circuit board by engagement of the upper edge of the tab with the bearing surface. part. 16. The electromagnetic shield of claim 15, wherein the shield is installed between the printed circuit board and the housing in the wireless telephone, and the housing is coupled to the upper edge of the tab to effectively press the electromagnetic shield to the printed circuit board. 10. The electromagnetic shield of claim 9, wherein each first tab protrudes into the shield. 10. The electromagnetic shield according to claim 9, wherein the shield is made of beryllium-copper. 10. The electromagnetic shield of claim 9, wherein the sidewalls and the spring contacts form a series of openings around the shield when the shield is installed on the printed circuit board. 20. The electromagnetic shield according to claim 19, wherein the maximum dimension of each opening is 6 mm or less. 10. The electromagnetic shield of claim 9, wherein the finger of the spring contact is located at the center of the sidewall. 10. The electromagnetic shield of claim 9, wherein a first fold line is provided between the sidewall and the first tab, and a second fold line is provided between the finger and the first tab extending from the first tab. 23. The electromagnetic shield of claim 22, wherein the finger is angled with respect to the first tab and is bent up and down relative to the surface of the shield. 10. The radiotelephone according to claim 9, wherein a shield comprising a surface, sidewalls and spring contacts is formed by a series of die cutting processes. A printed circuit board having an electrical circuit and a conductive strip extending around the electrical circuit; An electromagnetic shield disposed adjacent to the printed circuit board to insulate the electrical circuit disposed on the printed circuit board; A housing disposed adjacent the shield and surrounding the shield around the printed circuit board, The shield comprising a surface, a sidewall extending around at least a portion of the surface, and a series of spaced spring contacts extending from the sidewall of the shield for electrical contact with a conductive strip disposed on a printed circuit board, And the spring contact is flexible and vertically movable relative to the surface of the shield, wherein the shield with the surface and the sidewalls and the spring contact constitutes an integral structure formed of a conductive material. 27. The radiotelephone according to claim 25, wherein each spring contact comprises a first tab protruding from the plane of the side wall and a finger extending from the first tab. 27. The apparatus of claim 26, wherein the first tab protrudes outward from the sidewall of the shield and includes an upper edge, wherein the radiotelephone comprises a housing disposed opposite the electromagnetic shield opposite the printed circuit board, the housing being And a spring contact coupled with a conductive strip extending on the printed circuit board by engaging the upper edge of the first tab and effectively pressing the shield to contact the printed circuit board. 28. The radiotelephone according to claim 27, wherein a series of openings are formed on the shield and the printed circuit board. 29. The radiotelephone according to claim 28, wherein the maximum dimension of each of the openings is 6 mm or less. The radiotelephone according to claim 25, wherein said electromagnetic shield is made of beryllium-copper. 28. The system of claim 27, wherein the shield includes a second tab population spaced about the side wall and disposed between the spring contacts, the second tab projecting outwardly from the side wall parallel to the first tab of the spring contact. A wireless telephone, characterized in that. 33. The printed circuit board of claim 31, wherein the first and second tabs comprise an upper edge protruding outward from the sidewalls, wherein the shield is engaged with the upper edges of the first and second tabs to press the tab toward the printed circuit board. Cordless telephone, characterized in that pressed by the housing toward the printed circuit board. 33. The system of claim 32, wherein a first fold line is provided between the sidewalls and the first tab, and a second fold line is provided between the finger and the first tab extending from the first tab, wherein the finger is directed against the first tab. A radiotelephone having an angle and capable of bending up and down with respect to the surface of the shield. 27. The radiotelephone according to claim 25, wherein the spring contact protrudes inward from the side wall. 27. The radiotelephone according to claim 25, wherein each spring contact comprises a finger angled with the side wall. 27. The radiotelephone according to claim 25, comprising side spring contacts protruding outward from the shield for contact and grounding with the radiotelephone structure. A printed circuit board having an electrical circuit and a conductive strip extending around the electrical circuit; An electromagnetic shield disposed adjacent to the printed circuit board to insulate the electrical circuit disposed on the printed circuit board; An enclosure surrounding the shield, including a bearing surface for engaging the upper edge of the first tab, and a housing for urging the shield towards the printed circuit board such that the spring contacts engage with a conductive strip extending on the printed circuit board, The shield includes a surface, sidewalls extending around at least a portion of the surface at an angle with the surface, and a series of spaced spring contacts extending from the sidewalls, each spring contact protruding outwardly from the sidewalls. And a finger extending therefrom for electrical contact with a conductive strip integral with said first tab and formed with a conductive strip formed on a printed circuit board. 38. The radiotelephone according to claim 37, wherein the first tab is cut from the side wall of the shield and folded to protrude outward from the shield. 38. The radiotelephone according to claim 37, wherein both the surface, the side wall, and the spring contact are integrally formed. 40. The radiotelephone according to claim 39, wherein the electromagnetic shield is made of beryllium-copper. 38. A radiotelephone according to claim 37, wherein a series of openings are formed in the side wall of the shield. 42. A radiotelephone as claimed in claim 41, wherein the maximum dimension of each opening is 6 mm or less. 38. The electromagnetic shield of claim 37, wherein the second tab population protrudes from the side wall of the shield and the second tab is disposed between the first tabs. 44. The electromagnetic shield of claim 43, wherein the series of first and second tab pairs is formed in sets. 45. The electromagnetic shield of claim 44, wherein each tab set protrudes outward from the sidewall plane of the shield so that the tab set surfaces face each other. 38. The radiotelephone according to claim 37, comprising at least one side spring contact protruding outward from the side wall of the shield for electrical coupling and grounding with the radiotelephone structure.