Electrical Switch , of the Normally Closed Type, Especially for a Portable
Communication Device
The present invention relates to an electrical push button switch , of the normally
5 closed type , in particular intended for use with the keypad of a portable communication
device . The invention also relates to the manufacture of a flexible electrical contact keypad of
the normally closed type , the corresponding flexible keypad , the key and contact strip.
It should be reminded that a switch may flip between a closed position in which it
allows an electric current to pass , and an open position , in which it interrupts the flow or
1,0 passage of this electric current . A push button switch is said to be of the normally closed type
when it is brought back to its closed position in the absence of external stress , and when it
passes into its open position when actuated by a user , particularly by means of the push
button.
The current membrane keypads that are extremely fine and inexpensive are
15 manufactured by printing silver based conductive ink tracks on plastic substrates in order to
create extra fine circuits.
The keys of the keypad thus formed are all executed according to the same principle:
at least two tracks are arranged facing one another and are contacted when the key is
pressed . These keys are therefore normally open type electrical contact keys.
20 The electrically conductive member that enables the contacting is, as appropriate,
either a metal cup forming a cup contact , or a silver dot printed on the back of the upper
circuit or the back of the decorative face placed on the circuit . This type of contact is thus
designated as comb contact with flat or thermoformed front face.
The above techniques enable the production of membrane keypads, which have
25 reduced thicknesses of the order of 1 to 1 . 5 mm, or in the most elaborate cases, even of 0.6
to 0.7 mm.
The development of the aforementioned techniques has made it possible, more
recently to integrate extra fine components into membrane keypads , components such as
light emitting diodes LED or small resistors , whose thickness of the order of 0.5 mm allows
30 their integration in these fabrications.
However , when the use of more complex components appears to be necessary, it is
imperative to change the technology . Larger circuits are then most often bonded on to
machined metal plates , which are used to support the integration of buttons , switches,
emergency stop buttons or other elements.
35 When integrators of such circuits or keypads wish to take advantage in this type of
circuit or keypad of one or more normally closed type electric contact keys , in which two or
2
more conductive tracks are in permanent contact, the action of an operator on one of
the keys serving to open the contact , it is now necessary to either integrate buttons that are
bulky and constraining in terms of implementation costs , or to introduce electronic
management of this type of contact, which many integrators do not want to or cannot
5 execute.
For example , from the technical state of the art, in particular from EP 0 793 246, an
electric push button switch , of the normally closed type is already known. Such a switch
conventionally comprises a printed circuit , comprising first and second contact pads, and an
electrical conductor for electrically connecting the first and second contact pads.
10 Such a switch of the normally closed type has numerous elements , and therefore is
particularly costly and complex to implement. Moreover, on account of its complexity and
size, such a switch is not generally suitable for the keypad of a portable communication
device.
The present invention aims to overcome these drawbacks by providing an electric
15 push button switch, of the normally closed type, having a structure that is simple, economical
and compact.
Specifically, the invention relates in particular to the implementation of a process for
the manufacture of a flexible electrical contact keypad of the normally closed type, of a
normally closed type contact key and a keypad having at least one such key, while retaining
20 the advantages inherent in the flexible keypad technology, namely :
- maintaining a very thin keypad, its thickness not exceeding 1 to 1.5 mm, according
to the construction ;
- conservation of the operating principle of cup or thermoformed keys that are used in
membrane keypads at the present time ;
25 - maintaining a manufacturing cost structure that is competitive and compatible with
the specifications of existing markets that are seeking quality products at low costs ;
- obtaining a type of key that can function hundreds of thousands of times, or more,
without any reasonably foreseeable problems ;
making available a semi finished product that is easy to implement for integrators
30 without additional constraints related to adaptation of their working methods
- producing a final product, that is a flexible membrane keypad, durable enough to
withstand sometimes difficult conditions of use such as vibration, shock or other conditions.
An object of the present invention is in particular the implementation of a method for
the manufacture of a flexible membrane keypad comprising of at least one normally closed
35 type contact key.
3
This method is remarkable in that it consists at minimum, of equipping the keypad
with at least one circuit board printed on both sides comprising of at least one front contact
face and one back contact face ; of providing in the printed circuit , between the front contact
face and the back contact face, an insertion slot; of inserting into the slot one flexible
5 conducting strip forming a normally closed electrical contact between the front contact face
and the back contact face, this flexible conducting strip having a pressure point so as to
enable the exertion of a force for breaking the normally closed electrical contact.
Advantageously , the flexible conducting strip comprises of a flexible centre tab that
includes the pressure point, which is electrically and mechanically joined and adjacent to a
10 first side tab and a second side tab by a common point , the first and the second side tabs
being placed in one and the same plane and the centre tab being arranged in an offset
position in an orthogonal direction to said plane so as to form a first and a second insertion
space for inserting the flexible strip in the slot , the operation consisting of inserting includes at
least one step consisting of inserting said flexible strip into the slot by clipping of the first and
15 second insertion space on the opposite edges of the slot, in a manner so as to bring the
flexible centre tab to rest and respectively at least one of the first or second side tabs in
electrical contact with the back contact face and respectively the front contact face or vice
versa.
Preferably , the pressure point provided on the centre tab is placed in distant offset
20 position on the centre tab in relation to the common point so as to form a cross-force lever
between the contact point of the centre tab on the back or front contact face and the common
point.
Another object of the present invention is the implementation of a flexible contact strip
of normally closed type for the double sided printed circuit board.
25 Such a flexible contact strip is remarkable in that it comprises at least one flexible
centre tab, and a first side tab and a second side tab that are electrically and mechanically
joined to the same common point . The electrically and mechanically joined first side tab and
second side tab are substantially placed in the same plane, laterally adjacent to the flexible
centre tab . The centre tab is arranged in offset position in an orthogonal direction to the plane
30 so as to form a first and a second insertion space for inserting the printed circuit board that is
provided with one slot and at least one front contact face and one back contact face each
disposed in the vicinity of one of the two opposite edges of the slot.
Advantageously, the contact face of the flexible centre tab is formed by a boss, and,
optionally , the contact faces of the first side tab and the second side tab are also formed by a
35 boss.
4
Preferably, the flexible centre tab is offset at rest in an oblique plane in relation to
the plane containing the first flexible side tab and the second flexible side tab to form by
opposite constrained rotation of the flexible centre tab, the first and second insertion spaces
of the printed circuit board between this flexible centre tab and the first and second side tabs,
5 respectively.
Advantageously , the strip has been derived from the cutting / stamping of a sheet of
conductive material.
Another object of the present invention is the implementation of a contact key for the
flexible membrane keypad , such a contact key being remarkable in that it comprises of at
10 least one printed circuit board provided with at least one front contact face and one back
contact face , each placed in the vicinity of one of the opposite edges of a slot provided in the
printed circuit board , and a flexible contact strip according to the invention inserted into the
slot and forming a normally closed electrical contact between the front contact face and the
back contact face. The flexible strip includes a pressure point for enabling the exertion of a
15 force for breaking the normally closed electrical contact.
Advantageously, the pressure point can be actuated by pressure on a cup or a touch
pad disposed over it.
The invention also relates to a flexible membrane keypad having at least one
corresponding key and / or one flexible contact strip of the normally closed type.
20 The manufacturing process , the corresponding keypad and the normally closed type
electrical contact key, objects of the invention , find application in the manufacture of keypads
of all sizes , in particular small size keypads for mobile portable phone devices , personal
digital assistants (PDAs) and keypads and keyboards of larger dimensions such as keypads
and keyboards for laptops or desk top computers , musical instruments or the like.
25 The invention also relates to an electrical push button switch , of the normally closed
type , in particular intended for a portable communication device keypad , comprising of :
- a printed circuit board , including first and second contact pads, and
- an electrical conductor, designed for electrically connecting the first and second
contact pads,
30 characterised in that:
- the printed circuit has at least locally a generally plane shape and comprises of a
first face bearing a first contact pad, a second face, opposite the first, bearing a second
contact pad , and a through-orifice allowing access between the first face and the second
face,
35 - the conductor comprises of a first part , which cooperates with the first contact pad,
and
5
- the conductor comprises of a second part, which extends between a first end, fixed
to the first part , and a free second end, passing through the orifice , the second part is
elastically deformable between a rest position , in which its second end cooperates with the
second contact pad, and a stressed position , in which its second end is moved away from the
5 second contact pad.
Such a switch has a particularly simple structure , wherein the conductor cooperates
with the two contact pads without any intermediary and for which it is sufficient to apply a
force on the second part of the conductor in order to move this second part away from the
second contact pad, and thus open the switch.
10 Such simplicity of structure is possible in particular thanks to the contact pads
arranged on the opposite faces of the printed circuit.
In an optional manner, an electric switch according to the invention may include one
or more of the following characteristics , taken alone or based on any of the technically
feasible combinations :
15 - the switch comprises of a metal cup pusher , accessible from the side of the first face
of the printed circuit, and movable between a rest position, in which the second part of the
conductor is in its rest position , and an engaged position , in which the metal cup cooperates
with the second part of the conductor in order to keep it in its stressed position,
- the second part of the conductor has a boss provided between its first and second
20 ends , meant for cooperating with the metal cup when the metal cup is in its engaged
position,
- the first part of the conductor comprises of two branches and a base , so as to have
a U-shape , the two branches being arranged on either side of the orifice of the printed circuit,
- the second part of the conductor forms a small strip extending the base of the first
25 part , and extending longitudinally between the two branches of the first part,
- the first and second parts are formed integrally, with the . conductor for example,
being of sheet metal, and
- the switch comprises of means for backlighting, arranged on the side the second
face of the printed circuit, and
30 - the switch includes sealing means covering at least the metal cup and the
conductor.
The invention will be better understood upon reading the description which follows,
given solely by way of example and by making reference to the accompanying figures in
which:
35 - Figures 1a to ld shows the essential steps for implementing a method for
manufacturing a flexible keypad according to an exemplary embodiment of the invention ;
6
- Figure 2 shows a view from the top of a normally closed type flexible contact strip
for double sided printed circuit board in conformity with the object of the present invention ;
- Figure 3 shows a cross sectional view along the BB sectional plane of the normally
closed type flexible contact strip illustrated in Figure 2 ;
5 - Figure 4 shows a cross sectional view along the plane of the Figure Id of a normally
closed type electrical contact key according to the object of the present invention.
- Figures 5 and 6 respectively show views from above and below of an electrical
switch according to a second exemplary embodiment of the invention ;
- Figures 7 and 8 are cross sectional views of the switch in Figures 5 and 6,
10 respectively , in the closed position and the open position.
In the above mentioned figures the relative proportions of the elements have not
necessarily been respected , so as not to affect the overall clarity of the illustrations.
The method of manufacturing a flexible membrane keypad according to the object of
the present invention is now described in a detailed manner in connection with Figures 1a to
15 Id.
In step 1, shown in Figure la, the method according to the invention consists in
providing and equipping the keypad with at least one double sided printed circuit board Cl
comprising of at least one front contact face PR and one back contact face PV.
The double sided printed circuit board Cl can be formed by a printed circuit board of
20 any type, a double faced circuit or otherwise.
Step 1 is followed by a step 2, shown in Figure 1b, consisting of providing, in the
printed circuit Cl, between the front contact face PR and the back contact face PV, an
insertion slot. Preferably, but without being limited thereto, the insertion slot F is formed by a
slot with parallel edges, going through the entire thickness of the printed circuit board Cl.
25 Step 2 is followed by a step 3 comprising of a sub step 3 (1), shown in Figure 1c,
consisting of inserting in the insertion slot F one flexible conducting strip LS forming a
normally closed electric contact between the front contact face PR and the back contact face
PV.
As further shown in the drawings, the flexible strip LS has a pressure point PA that
30 enables the exertion of a force for breaking the normally closed electrical contact.
Moreover, in sub step 3 (2), represented in Figure 1d, in a cross sectional view along
the AA sectional plane of the printed circuit board Cl of Figure 1c, the normally closed
electrical contact type contact key obtained upon insertion of the flexible strip LS has been
shown. It is understood, in particular, that the insertion operation consists of introducing the
35 flexible strip LS by clipping, or by any other means, on each of the parallel edges of the slot
F, as will be described below.
7
For this purpose, during step 3 (1) shown in Figure 1c, the flexible strip LS may
include, preferably, a flexible centre tab LC including the pressure point PA, to which is
electrically and mechanically joined by a common point PC, and a first side tab LL1 and a
second side tab LL2. The flexible centre tab LC is adjacent and parallel to the first side tab
5 and the second side tab LL1 and LL2 and joined to the latter by the common point PC.
Preferably, the first and second side tabs LL1 and LL2 are placed substantially in the same
plane P but the centre tab LC is arranged in an offset position in an orthogonal direction to
said plane P, in order to form a first insertion space Ell and a second insertion space E12,
each included between the second flexible tab LC and the opposite ends of the two side tabs
10 LL1 and LL2.
It is thus understood that, in step 3 (1) shown in Figure 1c, the operation of insertion
of the flexible strip LS in the slot F is carried out by insertion and clipping of respectively the
first insertion space EL1 and the second insertion space EL2 on one of the opposite edges of
the slot F, in a manner so as to bring to rest the centre tab LC, respectively the two side tabs
15 LLI and LL2 electrically contacting respectively the back contact face PV and the front contact
face PR or vice versa.
Finally it can thus also be observed in Figure 1, that the pressure point PA provided
on the centre tab LC is placed in distant offset position on the centre tab in relation to the
common point PC so as to form a cross-force lever between the contact point of the first
20 centre tab on the back or front contact face and the common point CR
A more detailed description of a normally closed type flexible electric contact strip
specially designed for the implementation of the process, of a contact key and a flexible
membrane keypad in accordance with the object of the present invention will now be given in
connection with Figures 2 and 3.
25 In Figure 2 is shown the normally closed flexible contact strip according to the object
of the invention comprising of at least one flexible centre tab LC, to which it is electrically and
mechanically joined at the common point PC.
The flexible strip LS further consists of the first side tab LL1 and the second side tab
LL2 each being electrically and mechanically joined by the common point PC.
30 The first and the second side tabs are adjacent and parallel to the flexible centre tab
LC, but are arranged to be offset in position in an orthogonal direction to the plane P so as to
form the first insertion space Ell and the second insertion space E12 for the printed circuit
board Cl that is provided with the slot F, and the front contact face and the back contact face
disposed in the vicinity of the two opposite edges of this slot. With reference to Figure 2, it is
35 understood that the plane P substantially including the side tabs is none other than the plane
of the sheet carrying the above mentioned Figure 2 and that the insertion spaces Ell and EI2
8
shown between the parallel tabs on Figure 2, however, extend in a direction that is
orthogonal to the plane of the same sheet, as will be explained below in connection with
Figure 3.
With reference to the above mentioned figure, it is clear that the flexible centre tab LC
5 is offset at rest in an oblique plane PO in relation to the plane P containing the first flexible
side tab LL1 and the second flexible side tab LL2 in order to form, through opposite
constrained rotation of this flexible centre tab LC, the first insertion space Ell of the printed
circuit board CI between this flexible centre tab LC and the first and second side tabs LL1
and LL2. The angle of inclination of the oblique plane PO in relation to the above mentioned
1,0 plane P may be between 100 and 20°, depending on the elasticity characteristics of the
metallic material constituting the flexible strip LS.
In Figure 3, the movement of the centre tab LC is shown in dotted lines, in opposite
constrained rotation f so as to form the first insertion space Ell mentioned above.
The flexible strip LS can thus be clipped at its insertion spaces E12 and E12 by
15 performing opposite constrained rotation on the flexible centre tab LC in order to enable this
centre tab to pass under the printed circuit Cl, the latter entering, by the corresponding edge
of the slot F, in the first insertion space Ell; and to enter into electrical contact with the back
contact face PV, then, by displacement of the flexible strip LS, towards the opposite edge of
the slot F, so as to bring the latter into the second insertion space E12 and make electrical
20 contact between the front contact face PR and the flexible side tab or tabs LL1, LL2.
Thus, it is to be understood that the centre tab LC makes it possible to ensure the
function of breaking of the normally closed electrical contact by applying a stress on the
pressure point PA in cooperation with the flexible side tabs LLI1 and LL2.
The flexible strip as shown in Figures 2 and 3 above, is advantageously derived from
25 cutting / stamping of a sheet of conductive material such as a soft metal like copper-beryllium
alloy, steel or some other similar materials.
In particular the pressure point PA provided on the centre tab LC is advantageously
formed by a boss, for example. Similarly, the contact face PcC1 of the flexible centre tab LC
is formed, for example, by a boss. In addition, optionally, the contact faces PcL1, PcL2
30 respectively of side tabs LL1 are also formed by a boss, according to the present
embodiment.
A contact key for flexible membrane keypad, according to the object of the invention is
now described in connection with Figure 4.
With reference to the above mentioned figure, the contact key comprises of the
35 printed circuit board Cl equipped with the front contact face PR and the back contact face PV
each placed in the vicinity of one of the opposite edges of the slot F provided in the printed
9
circuit board . A flexible contact strip LS, as previously described in connection with
Figures 2 and 3, is inserted into the slot F so as to form the normally closed electrical contact
between the front contact face PR and the back contact face PV. The flexible strip includes
the pressure point PA for enabling the exertion of the force for breaking the normally closed
5 electrical contact. As was additionally also shown in Figure 4 , the above mentioned pressure
point can be activated by exerting pressure either on a cup C that is round in shape or on a
touch pad PT, arranged above it . The connection between the pressure , point PA and the
cup C or the touch pad PT is made in the conventional manner.
Finally , the invention relates to a flexible membrane keypad provided with a contact
1.0 key forming a normally closed type electrical` contact as described in connection with Figure
4. It is to be understood in particular that the key shown in the above mentioned figure can be
integrated to form a flexible keypad compatible with all types of materials for the front face
FA, such as polyethylene terephthalate (PET), elastomer, Polyurethane (PU), Polycarbonate
(PC) or other similar materials.
15 Shown in Figures 5-8 is an example of push button electric switch 10, of the normally
closed type . Such a switch is for example , designed to equip a keypad of a portable
communication device , such as in particular mobile phones or portable radios.
The switch 10 includes a printed circuit 12 of generally plane shape , having a first
face 12A and a second face 12B opposite to the first face 12A.
20 The first face 12A is generally an upper face intended to be turned towards the
exterior of the portable communication device . This first face 12A is in particular shown in the
Figure 1.
The second face 126 is generally a lower face , intended to be turned towards the
inside of the portable communication device. This second face 12B is shown in particular in
25 Figure 2.
The printed circuit 12 has a through orifice 14, allowing access between the first face
12A and the second face 12B. In the example shown, the orifice 14 has a generally
rectangular shape in the plane of the printed circuit 12.
As shown in Figure 1 , the printed circuit board has on its first face 12A, a first contact
30 pad 16 , also known as contact face . This first contact pad 16 has for example a U -shape and
is arranged around the orifice 14 in such a manner that the orifice 14 is partially framed by
this first pad 16, along the lengthwise sides and one breadthwise side of this rectangular
orifice 14.
As is shown in Figure 2 , the printed circuit 12 includes , on its second face 12B, a
35 second contact pad 18, also known as the contact face, for example of generally rectangular
10
shape . Preferably, the second contact pad 18 is arranged close to the second
breadthwise side of the rectangular orifice 14.
The switch 10 also includes a conductor 20, in the form of a flexible conducting strip,
designed for electrically connecting the first 16 and second contact pads 18.
5 The conductor 20 comprises a first part 22, such as shown in Figure 1, cooperating
with the first contact pad 16. Preferably, this first part 22 comprises of two branches 22A,
forming the side tabs, and a base 22B, forming a common point between the side tabs, so as
to have a U -shape also The branches 22A are arranged on both sides of the orifice 14 of the
printed circuit 12, along its lengthwise sides , in such a manner that the orifice 14 is partially
10 framed by this first part 22 in the plane of the orifice 14.
The conductor 20 includes , in addition , a second part 24 extending between a first
end 24A connected to the first part 22, and a second free end 24B designed to cooperate
with the second contact pad 18.
Preferably, the conductor 20 is made of sheet metal, the first 22 and second 24 parts
15 having been formed integrally.
In the example shown, the second part 24 of the conductor forms a strip (or flexible
centre tab) extending the base 22B of the first part 22, and extending longitudinally between
the two branches 22A of this first part 22. This strip 24 passes through the orifice 14 so as to
electrically connect the first part 22 with the second contact pad 18.
20 The second part 24 is elastically deformable between a rest position , shown in Figure
3, in which its second end 24B cooperates with the second contact pad 18, and a stressed
position , shown in Figure 4, in which its second end 24B is moved away from the second
contact pad 18. Thus, the switch 10 is in the closed position when the second part 24 is in its
rest position , and it is in its open position when the second part 24 is in its stressed position.
25 Advantageously , the second part 24 comprises , at its second end 24B, of a boss 25,
also called contact face , facilitating contact with the second pad 18. .
It should be noted , that due to the elastically deformable structure of the conductor
20, this conductor 20 can be assembled on the printed circuit board 12 by. the pinching of the
printed circuit 12 between the first 22 and second 24 parts of the conductor 20. This
30 assembly is particularly stable, thanks to the U-shape of the first part 22. This structure thus
facilitates the assembly of the switch 10.
The switch 10 also comprises a metal cup 26 of conventional type, forming a
pusher/push button, accessible from the side of the first face 12A of the printed circuit 12.
This metal cup 26 is arranged above the conductor 20, so that it is capable of cooperating
35 with the second part 24 of the conductor 20. To this end, as shown in Figure 1, the metal cup
26 is for example arranged in abutment on the first part of the conductor 20.
11
Such a metal cup 26 can be pushed by a user, in a manner so as to be deformed
elastically between a rest position as shown in Figure 3, and an engaged position as shown
in Figure 4.
In its rest position, the metal cup 26 is held away from the second part 24 of the
5 conductor, which is also found in its resting position. The switch 10 is therefore closed. It
should be noted that the height of the metal cup 26 in its position of rest is usually about 1
millimeter. Thus, the switch 10 is compact and can be easily integrated into a compact
portable communication device.
In its engaged position, the metal cup 26 cooperates with the second part 24 of the
10 conductor to maintain it in its stressed position. The switch 10 is thus opened.
Advantageously, the second part 24 of the conductor 20 includes a boss 28, forming
a pressure point, provided between its first 24A and second 24B ends and intended to
cooperate with the metal cup 26 when the metal cup 26 is in its engaged position. This boss
28 makes it possible to ensure contact between the metal cup 26 and the second part 24.
15 Alternatively, the metal cup 26 could bear a similar boss meant for cooperating with the
second part 24.
It should be noted that when the user releases the metal cup 26, the metal cup 26
and the second part 24 of the conductor 20 return by elasticity to their respective rest
positions.
20 Preferably, the metal cup 26 is designed to form a hard point, in order to provide a
tactile sensation to the user when he actuates the switch 10 by pressing the metal cup 26
with a finger.
The switch 10 preferably comprises some sealing means (not shown), for example of
plastic material, covering at least the metal cup 26 and the conductor 20. The sealing means
25 may also include, on the user-side, an inscription relating to the operation of the switch 10.
Such sealing means preferably cover the entire keypad of the communication device
so that the device can be used in wet and aggressive environments.
On an optional basis, the switch 10 may also include means for back lighting,
arranged on the side of the second face 12B of the printed circuit 12. Indeed, thanks to the
30 orifice 14, it is possible to provide the switch 10 with back lighting in a simple and effective
manner.
The previously described switch 10 comprises of few elements, and thus it has a low
weight, as well as a low cost.
It should be noted that the invention is not limited to the embodiment that has been
35 described above, but may be presented in different variants without departing from the scope
12
of the claims . In particular, the characteristics of each embodiment described above may
be implemented in a manner equivalent to the other embodiment described.
13
CLAIMS
1. A method of manufacturing a flexible membrane keypad comprising of at least one
5 normally closed contact key, this method consisting at least , of the following:
- equipping said keypad with at least one double sided printed circuit (CI ; 12)
comprising at least one front contact face (PR, 16) and one back contact face (PV ; 18),
- providing an insertion slot (F, 14) in the printed circuit board between the front
contact face (PR, 16) and the back contact face (PV, 18),
10 - inserting into said slot (F, 14), a flexible conducting strip (LS, 20) forming a normally
closed electrical contact between the front contact face and back contact face, said flexible
strip comprising a pressure point (PA, 28) so as to enable the exertion of a force for breaking
the normally closed electrical contact,
characterised by the fact that said flexible strip (LS, 20) includes a flexible centre tab
15 (LC; 24) comprising said pressure point (PA, 28), that is electrically and mechanically joined
with and adjacent to a first side tab and a second side tab (LL1, LL2, 22A) through a common
point (PC ; 22B), the first and the second side tabs being located in one and the same plane
and the centre tab being arranged in an offset position in an orthogonal direction to said plane
(P) so as to form a first insertion space (Ell) and a second insertion space (EI2) for said
20 flexible strip (LS; 20) at said slot (F, 14), the operation consisting of inserting includes at least
one step consisting of inserting said flexible strip (LS, 20) into the slot (F, 14) by clipping of
respectively the first insertion space (Ell) and the second (EI2) insertion space on the
opposite edges of the slot (F, 14), so as to bring the flexible centre tab (LS, 24) to rest and
respectively at least one of the first or the second side tab (t..L1, LL2, 22A) in electrical
25 contact with respectively the back contact face (PV, 18) and front contact face (PR, 16) or
vice versa.
2. A method according to claim 1, characterised by the fact that the pressure point
(PA; 28) arranged on the central strip (LC, 24) is placed in distant offset position on said
centre tab in relation to the common point (PC ; 22B) so as to form a cross-force lever
30 between the contact point of the centre tab (LC, 24) on the back or front contact face and said
common point.
3. Normally closed type flexible contact strip for double sided printed circuit board,
characterised in that it comprises at least:
- one flexible centre tab (LC ; 24),
35 - a first and a second side tab (LL1, LL2, 22A) each electrically and mechanically
joined to the flexible centre tab (LC ; 24) at a common point (PC; 22B) positioned
14
substantially in one and the same plane, laterally adjacent to said flexible centre tab
(LC, 24), the first and second side tabs (LL1, LL2, 22A) being arranged in offset position in an
orthogonal direction to said plane to form a first insertion space (Ell) and a second insertion
space (EI2) of the printed circuit board provided with a slot (F, 14) and at least one front
5 contact face (PR ; 16) and one back contact face (PV; 18) disposed in the vicinity of the two
opposite edges of said slot (F, 14).
4. Normally closed flexible contact strip of claim 3, characterised in that the pressure
point (PA ; 28) on said centre tab (LC, 24) is formed by a boss.
5. Normally closed flexible contact strip according to one of claims 3 or 4,
1.0 characterised by the fact that:
- the flexible centre tab (LC ; 24) comprises a contact face (PcC ; 25) formed by a
boss, and / or
- the first side tab (LL1) and the second side tab (LL2) each have a respective contact
face (PcLI, PcL2) formed by a boss.
15 6. Normally closed flexible contact strip according to one of claims 3 to 5,
characterised by the fact that the flexible centre tab (LC ; 24) is offset at rest in an oblique
plane in relation to the plane containing the first and the second flexible side tabs (LL1, LL2,
22A) to form by opposite constrained rotation of the said flexible centre tab (LC, 24), the first
insertion space (Ell) and the second insertion space (El2) of the printed circuit board (Cl; 12)
20 between said flexible centre tab (LC, 24) and said first and second flexible side tabs (L1-1,
LL2, 22A) respectively.
7. Normally closed flexible contact strip according to one of claims 3 to 6,
characterised by the fact that said strip (LS, 20) has been derived from the cutting / stamping
of a sheet of conductive material.
25 8. Contact key flexible membrane keypad, characterised by the fact that it comprises
at least:
- a printed circuit board (Cl, 12) equipped with at least one front contact face (PR, 16)
and one back contact face (PV, 18) each placed in the vicinity of one of the opposite edges of
a slot (F, 14) provided in the said printed circuit board,
30 - a flexible contact strip (LS, 20) according to one of claims 3 to 7 being inserted in
said slot (F, 14) and forming a normally closed electrical contact between the front contact
face (PR, 16) and the back contact face (PV, 18), said flexible strip (LS, 20) having a
pressure point (PA ; 28) for enabling the exertion of a force for breaking the normally closed
electrical contact.
35 9. Contact key for flexible membrane keypad according to claim 8, comprising a cup
(C ; 26) or a touch pad (PT), disposed above the pressure point (PA, 28), capable of
15
cooperating with this pressure point (PA, 28) for the actuation by pressure on this cup (C ;
26) or the touch pad (PT).
10. Flexible membrane keypad, characterised by the fact that it comprises at least one
key according to one of claims 8 or 9.