FR2752141A1 - PROTECTION FOR AN ELECTRICAL CIRCUIT ON A SUBSTRATE - Google Patents

Abstract

Protection is provided for an electrical circuit (104) which is disposed on a substrate (102). The protection includes a base (106) to be mounted on the substrate (102) and a one piece cover (108). The one-piece cover is joined to the base by filaments (220). The filaments are broken when the cover is pulled in one piece to separate it from the base. A replacement cover (700) includes fingers (702) which engage the base when the one-piece cover has been removed.

Description

Headline

  PROTECTION FOR AN ELECTRICAL CIRCUIT ON A

SUBSTRATE

  Field of the Invention The present invention generally relates to electromagnetic protection assemblies, and more particularly to a method and an apparatus for protecting an electrical circuit which is arranged on

a substrate.

  TECHNOLOGICAL BACKGROUND OF THE INVENTION Radiotelephones, pagers, transceivers, computers, and other electronic equipment often generate electromagnetic signals in a part of the electronic equipment which can send rays toward and interfere with another part of the electronic material. In order to minimize this interference effect, an electrically conductive (and sometimes magnetically conductive) material is interposed between the two parts of the electronic circuit. This protection can take the form of a wall or a complete enclosure and can be placed around the part of the electronic circuit which generates the electromagnetic signal and / or can be placed around the part of the electronic circuit which

  is sensitive to the electromagnetic signal.

  Existing electromagnetic protections are generally formed from a sheet of metallic material having a plate element suitable for positioning above a circuit component element (or an entire circuit), and include side flange portions which extend downward to cover side portions of the circuit component element. To function properly, the protection must be electrically coupled to the electrical circuit over which the protection is positioned. Consequently, one-piece protections are usually soldered to the electronic circuit in an o position.

  they can fulfill their protective function.

  Unfortunately, such a permanent fixture is difficult to remove if repairs are required. In order to avoid permanent attachment, other attempts at electromagnetic protection include the use of multiple components which use pressure fingers or finger-shaped flanges to produce contact between them. For these protections to function optimally, multiple points of contact between the components of the protection must be maintained. Notches for double U-shaped cantilever spring, such as those described in US Patent No. 4,890,199 allow the removable protections or else the raised areas of the housing to engage in the spring notches. However, an additional area of printed circuit boards is necessary to use the numerous notches which retain the removable protection or else the raised housing area. Another variant includes protections comprising removable covers provided with flanges at angles similar to springs which allow a solid fixing on the walls which extend from the printed circuit board. Although they can be dismantled, the flanges must be long and the walls must be high to allow secure fixing. Printed circuit boards with electromagnetic protection assemblies of this type require an increase in the volume of the chassis which houses the

printed circuit board.

  Miniaturized electronic devices impose even greater constraints on protections, firstly because the electronic circuits are closer to each other, and secondly because the space available for protection is greatly reduced. The techniques for securing or surrounding the electronic circuit with protection must take as little space as possible while providing interconnections which are easy to manufacture and easy to repair. A particularly advantageous protective assembly has been proposed which comprises a cover which slides on a base. The base is fixed on the printed circuit board. The cover is attached to the base and can be easily removed to give access

  to a circuit module located under the protection.

  The assembly has the advantage of requiring a minimum number of printed circuit boards while allowing a low profile enclosure, compared to the electromagnetic protection techniques of the prior art. However, the cover assembly can be relatively expensive. This expenditure is useless if the circuit located under the protection has

never need repairs.

  Therefore, there is a need for low cost protection, for an electrical circuit which emits, or is sensitive to, electromagnetic energy, which requires minimal space resources and which provides easy access to the electrical circuit when repairs are required.

Brief description of the drawings

  Figure 1 is an exploded perspective view illustrating a substrate assembly comprising an electromagnetic protection which must be positioned

on a substrate.

  FIG. 2 is an enlarged plan view from above illustrating the electromagnetic protection according to the

figure 1.

  Figure 3 is a cross-sectional view illustrating the electromagnetic protection along the

plan 3-3 of figure 2.

  Figure 4 is an enlarged fragmentary view of a

protection corner.

  Figure 5 is an enlarged view of another mode

making a filament.

  Figure 6 illustrates a perspective view of a

  assembly of assembled electromagnetic substrate.

  Figure 7 is an exploded perspective view of the assembly according to Figures 1 to 6, the cover in one piece being removed from the protection and a replacement cover to be positioned on the base. FIG. 8 illustrates the replacement cover assembled on the base of the protection, according to FIG. 7, fixed on the substrate. Figure 9 illustrates a cross-sectional view of the electromagnetic shield assembled along the

plan 9-9 of figure 8.

  Description of the preferred embodiments

  The protection 101 can be described in more detail with reference to FIGS. 1 to 6. The protection 101 is fixed on a substrate 102. The substrate can be any suitable element to which the circuit is connected, such as a wafer of printed circuits. Circuit 104 includes components, such as an integrated circuit. The substrate 102 preferably includes a printed circuit board material, such as a polyimide, FR4, or a cyanate ester. In a preferred embodiment, the substrate 102 and the electrical circuit 104 are housed inside an electronic device, such as a portable radiotelephone. The circuit 104 can thus be electrically connected to other elements (not shown) forming the electrical circuit of a radiotelephone, a digital cellular telephone, a cordless telephone, an analog cellular telephone, a pager, person

transceiver, or the like.

  FIG. 1 illustrates an exploded perspective view of a substrate assembly 100 comprising an electromagnetic protection 101 which must be positioned on the substrate 102. The electromagnetic protection 101 comprises a base 106 and a cover 108 in one piece, substantially planar and easily removable. The cover 108 in one piece and the base 106 are preferably formed in one piece, so that they are homogeneous and form a resistant protective structure and inexpensive to manufacture and assemble. Protection 101 is made from suitable electrically conductive materials, such as stamped steel from 1010 to 1018 and having a thickness of between 0.1 and 0.3 mm, and in practice having a thickness of 0, 18 mm. The side walls 110 and the feet 112 on the protection are formed by stamping and folding, and the side walls thus have gaps 114 at each of the corners which aid in folding.

side walls 110.

  The base 106 comprises an upper rim (FIGS. 2 and 3) and the plurality of side walls 110. The side walls 110 of the base 106 extend downward from the rim 218 in order to form the walls of the electromagnetic protection 101 The side walls 110 have a predetermined height which is based on the maximum height of an electrical circuit 104 which must be protected by an electromagnetic protection 101. Depending on the type of circuit 104, the height of the side walls 110 may be less than

4.0 millimeters.

  The upper rim 218 circumscribes the cover 108 in one piece and extends substantially

  orthogonally to the side walls 110.

  The rim 218 is connected to the cover 108 in one

  single piece by 220 filaments in one piece.

  A plurality of feet 112 is positioned at the base of the side walls at separate intervals, and extends orthogonally to them. The feet must be welded on bases 120 (FIG. 1), on the substrate 102. The bases 120 are electrically connected to the ground of the circuit by conductors (not shown). The feet 112 are attached to the bases 120 by an appropriate means such as a solder or an electrically conductive epoxy in order to ensure a permanent electrical connection.

  reliable at a relatively low cost.

  The cover 108 in one piece is joined with the flange 218 by separable elements, which, in the

  illustrated embodiment, are filaments 220.

  The filaments 220 are grouped into layers 222. The filaments 220 inside the layers 222 are separated by small openings 224. Larger openings 226 are elongated openings provided between the filaments of the adjacent layers. The plurality of openings 224 and 226 substantially circumscribes the cover in one piece and defines the perimeter of the cover 108 in one piece, and thus defines a predetermined area above which the

cover 108 in one piece.

  Each of the filaments 220 includes a stripe 302 (FIG. 3) over its entire width. Stripe 302 is

  located at the end of the filament rim.

  This is an added advantage to ensure that the filament 220 will break along the flange 218 without tearing the flange. The stripe 302 is preferably generally in the form of a V-shaped notch, which creates a point at which the filament is substantially

  thinner than the average thickness of the filament.

  The width "w" (Figure 4) of the filaments 220 can vary to vary the force required to break the filaments. The width of the filaments can vary from 0.1 mm (millimeter) to 1 mm, and in practice, vary between 0.35 mm and 0.5 mm. For example, the filaments 234 may be wider than the filaments 236 in order to increase the resistance of the filaments 234 to tearing. For example, it can be seen that the device housing (not shown) rests against the cover 108 in one piece near the filament 234, and the forces exerted on the housing create a force which must be exerted on the cover in one piece. The filaments 234 may be wider to strengthen the connection so that the cover does not separate from the flange when the device housing is subjected to a force. The thickness "t" of the stripe 302 can also vary in order to adjust the force necessary to break the filament. The thickness "t" can have any suitable thickness, and, when put into practice had a thickness of between 0.07 mm and

0.9 nmm.

  All the filaments of the protection 101 (filaments 220 and 234, and 236) have edges 400 which are substantially orthogonal to the edges 402 of the flange 218. The angle a is thus 90 degrees and the corner 404 is pointed. This shape facilitates the dismantling of the cover in one piece without tearing the flange 218. According to another solution, the corners 502 (FIG. 5) can have notches, so that the edges 504 of the filaments 220 and the edges 506 of the flange 218 are at an angle A, less than 90 degrees. This helps reduce the likelihood that the flange 218 will tear, but increases the difficulty and cost of maintaining the tooling (not shown) used to stamp protection 101, since stamping tools will tend to wear out when used, which causes the corners 502 to be rounded off. The edge 406 between the edge 400 and an edge 408 of the cover 108 in one piece is rounded to help the filament remain

  attached to the cover in one piece.

  The cover 108 in one piece includes inspection openings 250 (only some of which are numbered, Figure 2) located on the entire cover in one piece. The inspection openings provide visual access to the circuit located under the protection and also provide access for a test probe (not shown). The protection may include a raised single piece 252 if the circuit 104 (shown in Figure 1) covered by it is higher than

the side walls 110.

  When the protection 101 is originally attached to the substrate 102 during the manufacturing process, the feet 112 are welded to the bases 120. The side walls circumscribe the circuit 104 (shown in FIG. 1). The cover 108 in one piece covers the predetermined area under the protection and thus defines a protected volume, with the side walls 110 and the substrate 102. The protection 101 is connected to the ground by the welded connection of the feet 112 and the bases 120 , ensuring a route

  low impedance for electromagnetic signals.

  The electromagnetic protection 101 is assembled and fixed on a substrate 102 so that the assembled electromagnetic protection substantially surrounds the electrical circuit 104. The base 106 rests on a receptacle zone 121 of the substrate 102. The receptacle zone 121 preferably comprises a copper tape which is electrically coupled to a ground plane (not shown) via plated through holes (not shown). The receptacle zone 121 has a geometric shape similar to that of the base 106 and substantially encircles the circuit 104 which must be protected by the electromagnetic protection 101. The side walls 110 are electrically coupled to the receptacle zone 121 by means of a solder or conductive epoxy. As long as the circuit 104 located under the protection 101 operates correctly, the protection ensures a

  protection against electromagnetic interference.

  The electrical circuit 104 can be any circuit that emits, or is sensitive to, electromagnetic energy - for example, an oscillator circuit, a microstrip transmission line, or a digital logic circuit. The filaments 220, 234, 236 are strong enough to prevent disassembly of the cover 108 in one piece during normal use of the substrate assembly housing the device 100, and the protection provides some physical protection for the circuit 104 in

  absorbing small impact forces.

  If the circuit 104 inside the guard 101 needs repair, the inspection openings 250 are used to inspect the circuit 104 both visually and using test probes. If repairs are required, the one-piece cover 108 is easily removed. This is done by a technician who grasps the cover in one piece at one of the inspection openings 250 (for example using tapered telephone pliers), and pulling the cover out in one piece. The cover 108 will come off, breaking at the level of the stripes 302 of the filaments 220. The filaments break cleanly along the stripes 302, the square corners 404 ensuring that the rim 218 does not tear. In addition, by locating the stripe 302 at the end of the base of the filament 220, the portion of the filament that remains after the one-piece cover has been torn (i.e., the portion of the filament between the stripe and the rim 218) is very short. The tearing force is thus exerted on the flange, which resists deformation much better than the filament, which makes it possible to significantly reduce the deformation of the material which remains after dismantling the cover in one piece. The base 106 remains firmly attached to the substrate 102, as shown in the

figure 7.

  A replacement cover 700 (Figure 7) includes a plurality of fingers 702 located at predetermined locations on the periphery of the replacement cover 700. The fingers 702 are springs that extend outward and downward from planar central body 704. In a preferred embodiment, the fingers 702 are formed as an integral part of the body of the replacement cover 704. In another embodiment, the fingers 702 can be attached to the planar body 704 by suitable means such as welding of

projections on the planar body 704.

  The replacement cover 700 also includes substantially rectangular projections 706 between the fingers 702. The projections 706 are substantially in the same plane as the central body, and extend outward from the planar body.

  704 to be placed on the rim 218 of the base 106.

  Replacement cover 700 and base 106 preferably include a compatible and suitable metallic material to minimize corrosion after assembly. In a preferred embodiment, the cover 700 is fabricated, using a known technique of progressive stamping, which in one practice was a 0.18 mm thick sheet of an elastic alloy of nickel-silver tempered , although any suitable thickness can be used. The material is elastic enough that the fingers 702

act as springs.

  The replacement cover 700 is joined with the base 106 to substantially contain the circuit 104 shown in FIG. 8. The replacement cover 700 is positioned above, and substantially adjacent to, the flange 218 of the base 106. The fingers 702 are aligned with an edge of a respective large opening 226 so that they do not come into contact with any residual material from a removed filament. The cover 700 is then pushed back, preferably by pressure, until the projecting joints 900 (FIG. 9) of the fingers 702 pass under the rim 218 and snap under the rim, the rim being pinched between the projections 706 and the fingers 702. The fingers 702 are springs which are compressed to slide beyond the rim and to be pressed against the rim 218 to lock under the rim 218 as soon as the joint 900 has passed over the rim. The protrusions 706 are placed firmly against the flange 218, are held in position by the fingers 702. The pinching of the fingers 702 and the protrusions 706 prevents the cover 700 from rattling or being dismantled - for example, due to vibrations - - by limiting any movement of the

cover 700 after assembly.

  Preferably, the projections are slightly curved so that a point 902 of each of the projections hooks to the flange 218. This hooking guarantees that there is an electrical connection with the base 106 through the projections. The electrical connection provides a shortcut to ground and thus a low impedance path to ground, since the impedance is proportional to the length of the path and the conductance of the replacement cover 700 and

from base 106.

  FIG. 8 illustrates a perspective view of an assembled electromagnetic protection assembly and

  repaired 800 which is positioned on the substrate 102.

  As described in detail above, the assembled electromagnetic protection assembly 800 includes the replacement cover 700 joined with the base 106, so that the cover 700, the flange 218 and the side walls 110 enclose the electrical circuit (not shown). ). Each finger 702 is locked on the flange 218 in order to provide a zone where electrical connections are possible between the cover 700 and the base 106. In addition to this electrical contact zone, the projections 706 are in contact with the flange 218 because of this. of a normal downward force which is exerted on the cover 700 thanks to the connections of the fingers 702 and to the flange 218. Thus, the completely assembled electrical protection assembly 800 provides a multiplicity of electrical contact points o the cover 700 is joined with the base 106, which increases the effectiveness of the protection provided by the assembled electromagnetic protection assembly 800. If desired, the replacement cover 700 can be welded to the base 106. However, the force elastic exerted by the fingers 702 crushes the flange 218 between the projections 706 and the fingers, which keeps it firmly in place

without welding.

  The protection provides a method and an apparatus for protecting an electrical circuit that is disposed on a substrate. With the present invention, the electrical circuit is sufficiently protected while a protective enclosure maintains a low profile and requires a reduced substrate area, compared to the protection techniques of the prior art, and at low cost. In addition, the protection facilitates access to the electrical circuit in the event that repairs are necessary. Access can be obtained by simply pulling the cover back in one piece. The replacement cover can then be attached to the base. The replacement cover should only be used in cases where repairs are required, which reduces the average cost of protection compared to the cost of using sets of

protection in all cases.

Claims (10)

  An electromagnetic shield (10i) which provides electromagnetic shielding to an electrical circuit (104) which is disposed on a substrate (102), the electromagnetic shield comprising: a base (106) having side walls having a predetermined height, the walls lateral defining a perimeter of a protected volume; a one piece cover (108) which extends from the base to define the top of the protected volume; and characterized in that fine, one-piece filaments (220, 234) connect the one-piece cover and the base, the one-piece fine filaments being separated by openings which circumscribe and substantially define the perimeter of the one-piece cover, the openings comprising at least one elongated opening (226), in which the one-piece cover is easily broken, from the bottom, without damage the base.   2. Electromagnetic protection according to claim 1, further characterized in that the one-piece filaments comprise a scratch (302).   3. Electromagnetic protection according to claim 2, further characterized in that the base further comprises a flange (218) which   circumscribes the cover in one piece.   4. Electromagnetic protection according to claim 1, further characterized in that the filaments in one piece (220, 234) are different widths.   5. Electromagnetic protection according to claim 1, further characterized in that the one-piece cover includes openings inspection (250).   6. An assembly comprising the electromagnetic protection according to claim 1, characterized in that a substrate (102) comprises a circuit deposited thereon; and the electromagnetic protection is mounted on the substrate, the protection base is dimensioned so as to circumscribe at least part of the circuit, the   base being electrically connected to the circuit.   7. The assembly of claim 6, further characterized in that the scratches are at   the end of the base of the striped filaments.   8. The assembly of claim 6, further characterized in that it comprises a cover intended to be mounted on the base, the cover (700) comprising elastic fingers (702) which can slide over the edge and snap into place on the base under the edge and protrusions (706) which can be placed on the base, the elastic fingers holding the cover the base.   9. The assembly of claim 8, further characterized in that the resilient fingers include joints (900) which are positioned under the edge. 10. The assembly of claim 8, further characterized in that the protrusions are curved so that a tip of the protrusions hooks into the   basis for making an electrical connection to it this.