FR2687273A1 - SHIELDING METHOD AND ARMORED KEYBOARD OBTAINED BY THIS METHOD. - Google Patents

Abstract

The method of shielding a keyboard comprising in order a metal screen (2), at least two printed circuits (3 and 5) isolated by at least one insulating layer (4), the two printed circuits (3 and 5) and the insulating layer (4) constituting inner active layers (3, 4, 5) of the keyboard, and resting on a metal support (6), consists of covering the inner active layers (3, 4, 5) of the keyboard by the 'metal screen (2) without overflowing them, and to establish a ground contact (9) between the metal screen (6) and the metal support (6) through openings (8) made in the inner active layers (4 , 5, 6) of the keyboard. Application: protection against EMD and Tempest electromagnetic attacks of electronic equipment including keyboards.

Description

Shielding method and shielded keyboard

obtained by this method.

  The present invention relates to a shielding method and an armored keyboard obtained by this method for the protection

  electromagnetic equipment.

  One of the sensitive points in the shielding of electronic equipment is located at the keyboard The keyboard is a

  organ allowing an interactive or unidirectional exchange of

  training between a user and electronic equipment that processes this information The information entered first keyboards are translated in the form of electrical impulses that pass through the keyboard to the electronic equipment During this transit, they can, on the one hand be disturbed by a

  aggressive external magnetic environment, such as

  high power, electronic power tubes,

  strong explosions etc., generating electromagnetic radiation

  powerful techniques that can be translated into the team-

  by electronic errors in the transmission of information

  tions, see through the destruction of electronic components

  on the other hand, as any passage of current in an electric conductor is accompanied by an induced magnetic field and an electric field both proportional to the intensity of this current, the magnetic and electric fields, although weak, result in a electromagnetic radiation to the outside of the keyboard that can be detected and interpreted remotely from

  electronic equipment, and may also be the disturbing element

the environment.

  To protect oneself from the electromagnetic radiation

  from the outside and to protect the equipment against electromagnetic leakage directed to the outside, these protections respectively of type called EMP, abbreviation of

  Electro Magnetic Pulse, and Tempest, must meet the requirements of

  increasingly stringent requirements for the shielding of materials

  A known solution, described in US Pat. No. 2,621,209, for shielding a flat membrane keyboard, is to use a flexible metal shell to cover the printed circuit boards by overflowing the thickness of the keyboard and to fold the edges towards the back of the keyboard in order to come into contact on its periphery with the mass of the electronic equipment.

  on which is attached the keyboard This metal envelope-

  flexible mesh consists of a fine mesh metal mesh

  allowing the possible visualization of displays of the team-

  In the case where there is no display, the wire mesh

  the fines can be replaced by a flexible metal foil of

  low thickness fixed according to the same principle as for the grill-

  on which the indica-

  front panel of a keyboard.

  This solution, however, has several disadvantages.

  The grid, because of the overflow of the outer edges of the keyboard is subjected to frictional wear and deteriorates gradually no longer ensuring, in the longer or shorter term, effective shielding of the keyboard It is the same for the metal sheet , which because of its small thickness of the order of 50 to

  100 li meters, tear on its folding edges.

  For a keyboard with information display areas

  mations, for example liquid crystal displays, the meshing of the wire mesh too fine allows the light to pass

  difficult reading of the displays.

  The bonding of the mesh on the active inner layers of the keyboard is difficult because of the poor surface condition of the

  wire mesh which consists of intertwined conductive wires.

  The object of the invention is to overcome the aforementioned drawbacks.

  For this purpose, the object of the invention is a method of

  of a keyboard comprising in order a metal screen, at least two printed circuits isolated by at least one layer

  insulation, the two printed circuits and the insulating

  killing active inner layers, and resting on a sup-

  metal port, characterized in that it consists in covering the active inner layers of the keyboard by the metal screen without overflowing them, and in establishing a mass contact between the metal screen and the metal support through openings

  arranged in the active inner layers of the keyboard.

  The invention also relates to an armored keyboard

  produced by the process according to the invention.

  The invention establishing a mass contact across the

  keyboard between the metal screen and the metal support of the keyboard.

  Its main advantage is that it makes it possible to

  0 effective mechanical screen protection that can not be so

  damaged by rubbing against objects outside the keyboard.

  Moreover, no metallic element is in contact with the atmosphere.

  ambient sphere, thus avoiding keyboard corrosion.

  Other features and advantages of the invention are

  will be described below with the aid of the following description

  keeping the attached drawings which represent:

  FIG. 1, an exploded view in perspective for illustrating

  to create a first assembly mode of a keyboard implementing

  the shielding method according to the invention.

  FIG. 2 is a sectional view of the method of assembly shown in FIG. 1; FIGS. 3a, 4a, 5a and 6a have cross-sectional views of the embodiments of Uic metal contacts used for FIG. production of a shielded keyboard according to the invention; Figures 3b, 4b and 5b are perspective views illustrating the respective embodiments in Figures 3a, 4a and 5a; Figure 6b, an exploded perspective view illustrating

  the embodiment according to Figure 6a.

  3)) For the sake of clarity, the relative thicknesses of the different elements of the aforementioned figures have not been similarly respected, the elements common to each of the figures are identified by

their same landmark.

  FIG. 1 illustrates a particular embodiment of the shielding method according to the invention according to an exploded layering of several constituent layers 1 to 5 of a flat rectangular membrane keyboard designed to rest on a flat metal support 6 Figure, highlights a particular distribution of the mass contact around the entire perimeter of the metal support 6 Openings 8 arranged in the active inner layers 3, 4 and 5 of the keyboard allow the passage of metal contacts 9 The number, shape and

  The dimensions of openings 8 depend on the type of contact used.

  sé. The keyboard comprises respectively from the outside to the inside of the keyboard, or in the figure from right to left, a top layer 1 (or plastron) polycarbonate, can carry keyboard indications on its outer face, a metal screen 2 nickel-plated copper-beryllium alloy partially perforated on areas 10 i overlying, for example, displays

  not shown of the electronic equipment 7 represented f i-

  2, or keyboard keys also not shown.

  The perforated zones are formed by grids made

  the process described for example in the patent 2,638,596 filed by the Applicant, ensuring good visibility of

  display indications and sufficient flexibility of the

  the keyboard by not increasing the effort on the keys by

  compared to an unshielded keyboard The keyboard has three

  3, 4 and 5 in the order of one

  first flexible printed circuit 3, an insulated interlayer

  4 and a second flexible printed circuit 5, the printing faces

  of the two printed circuits 3 and 5 being opposite The different layers 1 to 5 are glued with a non-glue

  conductive, juxtaposed one on the other, and are themselves

  same glued by the same glue on a metal support 6 representing the front panel of electronic equipment 7 of

  the manner shown in Figure 2.

  In this figure, the 3 active inner layers 3, 4 and the keyboard constitute the three classic layers of an unscreened flat keyboard. These are perforated on their periphery.

  interior through the openings 8 to allow the passage of

  metal contacts 9 between the metal screen 2 and the metal support

  Contacts 9 are also distributed around the periphery

  inside the metal screen 2 and ensure the shielding of the

  v-ier pressing successive layers i to 5 glued, so

  metal contacts 9 between the metal screen 2 and the

  metal port 6 The four layers 2 to 5 are covered with the upper layer 1 also glued which can carry

  keyboard indications on its external face The dimensions

  five layers 1 to 5 glued to the metal support 6

  are advantageously provided slightly lower than the dimensions

  the metal support 6 to prevent overflow of

keyboard glue.

  All the embodiments of the method according to the invention described below have the same common characteristics.

described below.

  Thus, the mass contact between the metal screen 2 and the metal support 6 is provided by the multiple metal contacts 9 distributed over the inner periphery of the keyboard Each metal contact 9 is cut and preformed projecting from its cutting plane constituted by either the metal screen 2 or by

  a metal strip 12 attached to the metal support 6.

  One of their extremities is fixed and the other, free, is

  The contact 9 thus formed passes through the inner active layers

  3, 4, 5 through the openings 8 respectively facing each other from one layer to another and facing the contact 9 The * upper layer 1 is glued on the upper face of the screen

  2 The mass contact is ensured thanks to a deformation

  The quality of the contact depends mainly on the mechanical and electrical properties of the material used for its application. the elasticity and the conductivity of the material, and as an example it may be made of alloy

Nickel-plated beryllium.

  In the first embodiment, the metal contact 9 comprises, as shown in FIGS. 3a and 3b, a rectangular-shaped blade cut in the thickness of the metal screen 2, parallel to one of its edges and preformed to give with the blade a concave shape protruding from the face

  bottom of the metal screen 2.

  In the second embodiment, shown in FIGS.

  and 4 b the metal contact 9 has a flat rectangular blade

  laire whose free end is folded on itself.

  In the third embodiment described in Figures 5a and 5b, the same contact 9 is used but it is folded on the edge of the openings 8 arranged in the layers

  3, 4 and 5 In this case, the length of the

  8 is reduced compared to the other modes of

  The excess thickness introduced by the folding of the blade of the contact 9, is contained in a recess 11 dug in the metal support 6 corresponding to this thickness and whose tolerances -are adapted to ensure the mechanical mass and

electrical shielding.

  Finally according to the fourth embodiment, represented by FIGS. 6a and 6b, the metal contact 9 comprises a narrow metal strip 12 attached to the inner edge of the upper face of the metal support 6, one side of which is

  large dimension of the band 12 is free and outwardly oriented

  of the metal support 6 and serrated protruding from the formed plane

  by the flat strip 12, and the opposite side of which

  the metal support 6 is stuck on it.

  introduced by the thickness of the contact strip 12 is

  contained in a groove 13 arranged in the metal support

  6 opposite the contact strip 12 A number of teeth 14 corresponding to the dimension given to the opening 8 arranged in the inner active layers 3, 4 and 5 ensures the mass

  mechanical and electrical shielding.

  The shielding performance achieved by the process

  according to the invention could be quantified by a measure of the attenuation

  electromagnetic radiation emitted to the outside of the keyboard The effectiveness of the shielding could be measured against

  to a reference which is the case where the attenuation of the elec-

  magnetic pole is zero, so without any shielding, the

  limit of the measuring system being given by the maximum attenuation

  obtained in the case of a solid metal plate

the keyboard.

  Beyond f = 10 M Hz, it is the electric field that

  For this frequency the attenuation of the electric field

  The C + emitted towards the outside of the keyboard reaches about 110 dB. The invention is not limited to the embodiments of the shielding of a rectangular flat keyboard described in the present invention; the number of contacts, their shape, their size and their positioning can always be adapted according to the type of contact used and the useful dimensions of the keyboard to guarantee a mass contact, thus a shield whose performances are close to those of the In the same way, any keypad membrane type of any shape

  as well as the combination of several different types of

  tacts are within the scope of the present invention.

  The upper layer 1 can also be deleted All possible indications that can be reported directly

  on the upper face of the metal screen 2.

_ S

Claims (9)

  1 method of shielding a keyboard comprising in order a metal screen (2), at least two printed circuits (3 and 5) isolated by at least one insulating layer (4), the two printed circuits (3 and 5) and the insulating layer (4) constituting inner active layers (3, 4, 5), and resting on a   metal support (6), characterized in that it consists of   the inner active layers (3, 4, 5) of the keyboard by the metal screen (2) without overflowing them, and to establish a mass contact between the metal screen (2) and the metal support (6) through openings (8) arranged in the active layers inside (4, 5, 6) of the keyboard.   2 Method according to claim 1, characterized in that it consists in distributing the mass contact (9) on the periphery inside the keyboard.   3 keyboard, characterized in that it is realized according to the   process described in any one of claims 1 and 2   and in that the mass contact between the metal screen (2) and the metal support (6) has multiple metal contacts (9). 4 keyboard according to claim 3, characterized in that   the ground contact has metal contacts (9) which are   Pés and préformés projecting from their cutting plane, one end of which is integral with its cutting plane and the other is free.   Keyboard according to any one of claims 3 and   4, characterized in that each metal contact (9) is   and preformed in the thickness of the metal screen (2) protruding from the underside of the metal screen (2) to give elasticity to the contact   6 keyboard according to any one of claims 3 to   , characterized in that each contact (9) has a cut and preformed blade in the metal screen (2) giving the blade a concave rectangular shape projecting from the underside of the metal screen (2) to press on the support metallic (6).   Keyboard according to one of claims 3 to   , characterized in that each contact (9) comprises a cut and preformed blade giving the blade a rectangular shape   flat protruding from the underside of the metal screen (2).   8 keyboard according to claim 7, characterized in that the blade has a free end folded on itself for   press on the metal support (6).   9 keyboard according to claim 8, characterized in that the blade has a free end, folded over the edge of the openings (8) arranged in the inner active layers   (3, 4, 5) of the keyboard next to the blade.   Keyboard according to claim 3, characterized in that   mass contact between the metal screen (2) and the   metal port (6) has contact strips (12)   on the inner edges of the upper face of the metal support (6) each having at least one free side facing the outside of the metal support (6) and serrated along the large dimension of the free side of the contact strip (12) with a number of teeth (14) preformed projecting from their plane   the number of teeth (14) depends on the length of   the opening (8), facing the teeth (14), arranged in the inner active layers (3, 4, 5) of the keyboard, and the   opposite side to the free side being fixed on the metal support (6).