WO2016134735A1

WO2016134735A1 - Capacitive touch sensor and a method for assembling the capacitive touch sensor

Info

Publication number: WO2016134735A1
Application number: PCT/EP2015/000421
Authority: WO
Inventors: Pawel Meller; Bartosz DULSKI
Original assignee: Diehl Ako Stiftung & Co. Kg
Priority date: 2015-02-24
Filing date: 2015-02-24
Publication date: 2016-09-01
Also published as: EP3262757A1

Abstract

A capacitive touch sensor comprising a body (1) made of an electrically conductive elastic material and having a top wall (3) and a base (5) located opposite to the top wall (3) and at least one side wall (4) connecting said top wall (3) with said base (5) wherein said body (1) being mounted on a PCB (11) and the base (5) being electrically connected with a PCB copper area (10), whereas it comprises a metal coupling element (2; 12) fixing the body (1) to the PCB (11) and comprising a contact surface (20) adapted to be soldered to the copper area (10) of the PCB (11), wherein the contact surface (20) is located in the same plane as the outer surface of the body base (5).

Description

Capacitive touch sensor and a method for assembling the

capacitive touch sensor

Technical field The invention relates to a capacitive touch sensor (CT sensor) and a method for assembling the capacitive touch sensor .

Prior art

CT sensors are used in control units which are activated by a presence of a user's finger. In more detail, the user's finger approaching the control unit which includes the CT sensor, causes a change of the capacitance of the assembly, which is detected by a integrated circuit connected to the control unit and becomes a signal corresponding to the detection .

Control units using CT sensors are widely known and are used in domestic appliances (e.g. such as hobs) . CT sensors are mounted on a metallic contact surface of a printed-circuit board (PCB) and electrically connected with a suitable integrated circuit for receiving signals from the CT sensor. Next, the PCB with the CT sensor is placed under the glass plate being the top layer of the hob. Due to the body of the CT sensor is usually made of electrically conductive elastic material, e.g. silicone, PCB can be placed so close to the glass plate that the body of the CT sensor is pressed against the bottom surface of the glass plate, which assures close contact between the surface of the body and the surface of the glass plate. Thereby, the control unit is a capacitor comprising one capacitor plate being the conductive body of the CT sensor connected with the metallic contact surface of the PCB , and the dielectric being the glass plate. The electrical state of such capacitor is constant until an object changing its capacitance appears above the glass plate in proximity of the CT sensor. The change of the capacitance is detected by integrated circuit connected to the CT sensor. The appearance of such object, e.g. a user's finger, is interpreted as triggering of the control unit .

The publication No. US 2008/0190751 Al presents the structure of a CT sensor body made of an elastic, electrically conductive material. The sensor body has two parallel end wall areas being the top and bottom surfaces, which are integrally connected in one piece by inwardly cambered side wall areas. Such sensor body can be very easily compressed.

Due to a mass production of devices using CT sensors, there is a constant desire for new methods for manufacturing and assembly of CT sensors, which are fast, simple and does not require specific tools. One of the essential step of the assembly process is fastening the CT sensor body to the PCB.

One of the known methods of fastening the CT sensor body to the PCB is presented in EP 859467 Bl . The silicone body is glued to the surface of the PCB. Although gluing is the universal method of joining and can be used for different applications, it is very difficult from chemical point of view in case of conductive elastic bodies of CT sensors and requires special equipment which makes this method expensive in this technical field.

Another method, presented in EP 1559195 Bl, concerns fastening the CT sensor body using a support element, e.g. made of plastic or metal, which is integrated with the body and engages the corresponding opening in the PCB. No additional connection process is needed in this method, however the support element requires additional machining of the PCB in order to provide the opening for the engagement. The body itself also requires additional tools for forming or attaching the support element.

The publication EP 2532972 Al presents a CT sensor body made of elastic foam and surrounded by a metal film which provides electrical conductivity and allows positioning and soldering of the body to the PCB. Similar structure of the body is disclosed in EP 1672797 Bl, however in this publication the body is surrounded by a metal mesh appropriate for soldering. No additional equipment for fixing the body to the PCB is needed in this case, however surrounding the whole body by the metal film or mesh in view of the mass production of CT sensors leads to a huge consumption of the material surrounding the foam.

Objectives of the invention

The object of the present invention is to provide a CT sensor having simple and economical construction which allows fast assembling and securing to the PCB without using additional binding substances such as glue as well as without the need of a special adaptation of the PCB, e.g. drilling holes .

Moreover, the object of the present invention is to provide a method for assembling the CT sensor, which is simple, time saving, and requires only the equipment for surface -mount technology (SMT) , which is anyway needed for mass production of printed circuit boards .

Brief description of the invention

A capacitive touch sensor, in accordance to the invention, comprising a body made of an electrically conductive elastic material and having a top wall and a base located opposite to the top wall and at least one side wall connecting said top wall with said base wherein said body being mounted on a PCB and the base being electrically connected with a PCB copper area, is characterized in that it comprises a metal coupling element fixing the body to the PCB and comprising a contact surface adapted to be soldered to the copper area of the PCB, wherein the contact surface is located in the same plane as the outer surface of the body base.

Preferably, said body is hollow, and the body base comprises an opening which is surrounded by a flange extending in the plane of the base from the bottom edge of said at least one side wall, said at least one side wall comprises a protrusion extending generally parallel to the body base and inside the body, wherein said coupling element is a clip comprising a base having the contact surface attached to the PCB copper area, and at least one arm extending from the base towards said at least one side wall of the body, wherein the arm contacts the body pressing it towards the PCB.

Preferably, the clip is located in the opening and inside the body so said at least one arm is located between the protrusion and the flange of the body and contacts the flange pressing it against the PCB copper area.

Preferably, said at least one arm is plastically deformable between the free position in which said at least one arm extends at an angle to the clip base and the clamped position in which said at least one arm is generally parallel to the clip base overlapping the clip base flange.

Preferably, the clip is located outside the body and surrounds the body, wherein the at least one arm at least partially overlaps and contacts the outer surface of the side wall and the protrusion. Preferably, said body is solid and said coupling element is a plate having its contact surface integrally flush mounted in the body base .

Preferably, the plate extends over the whole outer surface of the body base.

Preferably, there is a central blind opening extending from the contact surface through the plate and the body.

Preferably, the body has a cylindrical shape.

Preferably, the body is made of the electrically conductive silicone.

Another aspect of the invention concerns a method for assembling the capacitive touch sensor comprising the steps of:

- providing the capacitive touch sensor according to claims 1-4;

- placing the coupling element on the copper area of the PCB and connecting the said coupling element with the copper area in the SMT process;

- placing the body of capacitive touch sensor aligned with said coupling element so said body base contacts the PCB copper area and the arms are placed between the flange and the protrusion of the body;

- applying a force directed towards the PCB to the top wall of the body and press it against the copper area of the PCB to attach the body to said coupling element and fasten the body to the PCB.

It should be noted that even though the metal coupling element (e.g. clip) is an additional part, it is very simple and economical element which is easy to manufacture using standard equipment. No additional investment is needed, because the clip is fitted for positioning and connecting with the PCB by soldering during the standard surface mount technology process (SMT) . Moreover, the same clip can be engaged with many different bodies which makes it universal. In this way, the clips can be soldered to the PCB and the particular type of bodies, having particular shape and size, may be attached later depending on the requirements. Additionally, coupling between the body and the 'clip is mechanical so no additional binding substances, like glue, is needed .

The advantage of the CT sensor having solid body integrated with the fastening element is that the body can be attached to the PCB in SMT process only and does not require any additional assembly steps. Moreover, as the body is electrically conductive by itself, a solderable fastening element is needed only in the base area of the body contacting the metallic contact area of the PCB, and the amount of the material for the fastening element is reduced in comparison to the prior art. Finally, it should be noted that the location of the fastening element only in the area of the base allows the body to have any shape necessary.

Description of the drawings

The embodiments of the invention are shown on the attached drawing in which:

Fig. 1 is a side view of the CT sensor in accordance with the first embodiment of the invention.

Fig. 2 is a perspective sectional view of the CT sensor body and the clip, in accordance with the first embodiment of the invention .

Fig. 3 shows a method of assembling the CT sensor according to the first embodiment of the invention.

Fig. 4 is a perspective sectional view of the CT sensor body and the clip, in accordance with the second embodiment of the invention .

Fig. 5 is a side view of the CT sensor in according to the third embodiment of the invention. Fig. 6 is a side view of the CT sensor body with the integrated metal plate, in accordance with the third embodiment of the invention.

Fig. 7 is a side view of another aspect of the CT sensor body with the integrated metal plate, in accordance with the third embodiment of the invention.

Fig. 8 is a side view of the CT sensor body with the integrated metal plate and the opening, in accordance with the third embodiment of the invention

Fig. 9 is a side view of another aspect of the CT sensor body with the integrated metal plate and the opening, in accordance with the third embodiment of the invention.

Description of embodiments

The first embodiment of the CT sensor is presented on Fig.

1. The CT sensor comprises a body 1 and a coupling element formed as a clip 2 for fixing the body 1 to the PCB 11. The body 1 is made of an elastic electrically conductive material and has essentially cylindrical shape. As shown also on Fig.

2, the body 1 comprises a top wall 3 and a base 5 connected by a side wall 4. The body 1 is hollow and the space inside the body 1 is limited by the internal surfaces of the top wall 3, side wall 4 and base 5. The base 5 comprises, in its central part, an opening 6 which connects the interior of the body 1 with its exterior. The part of the base 5 surrounding the opening 6 forms a flange 5a. The side wall 4 comprises an annular protrusion 7 extending generally parallel to the base 5, along the side wall 4 and inside the body 1.

The clip 2, shown on Figs. 1 and 2, is located in the area of the body base 5, and comprises a base 8 having the contact surface 20 contacting the PCB copper area 10, and arms 9 extending outside from the base 8 and away from the base surface 20. The arms 9 are positioned between the flange 5a and the protrusion 7. The clip is made of solderable and plastically deformable metal. Therefore, the arms have two operating positions: the free position in which the arms 9 are at the angle of about 45° to the base 8, and the clamped position in which the arms 9 are bent towards the plane of the base 8 and are generally parallel to it.

The distance between the ends of the arms 9 in the free position is greater than the diameter of the opening 6 in the base 5, however the distance between the ends of the arms 9 in the clamped position is smaller than or equal to the internal diameter of the side wall 4 of the body 1.

The assembly method of the CT sensor in accordance with the first embodiment is presented on Fig. 3. The first step comprises fastening the clip 2 to the PCB 11 by positioning the clip 2 with its base 8 on the copper area 10 of the PCB 11 and then soldering the clip contact surface 20 in the standard S T process.

Next, the body 1 is put on the clip 2 so the clip 2 passes the opening 6 in the body base 5 and is received inside the body 1. The arms 9 of the clip 2 are in the free position and are located between the flange 5a of the body base 5 and the protrusion 7 of the body side wall . Simultaneously, the body base 5 contacts the copper area 10 to which the clip 2 is soldered .

In the next step, a vertical force 15 directed towards the

PCB 11 is applied to the body top wall 3. The body 1 is elastically deformed and the protrusion 7 moves towards the PCB 11 pressing the clip arms 9 and deforming them into the clamped position in which the arms 9 press down the body base flange 5a against the copper area 10 of the PCB 11. In this way, the body 1 is secured to the copper area 10 of the PCB 11 so there is an electric contact between the body 1 and the copper area 10, and the CT sensor is assembled. In the second embodiment shown on Fig. 4, the clip 2 is located outside the body 1. The clip base 8, soldered to the PCB 11 with its contact surface 20, surrounds the body 1, and the arm 9, in a form of a flange, extends from the base 8 towards the external surface of the body side wall 4. In more detail, the arm 9 hooks the lower area of the external surface of the protrusion 7, fixing the body 1 in relation to the PCB 1 and pressing the body 1 against the PCB copper area 10.

In order to assemble the CT sensor in accordance with the second embodiment, the clip 2 is positioned with its base 8 on the copper area 10 of the PCB 11 and then its contact surface 20 is soldered to the PCB copper area 10 in the standard SMT process. Next, the base 1 is elastically deformed and installed inside the clip 2 so the body base 5 contacts the PCB copper area 10. The elasticity of the body 1 assures that it is reliably pressed against the PCB 11 by the arm 9 contacting the external surface of the protrusion 7.

The third embodiment, shown on Fig. 5, concerns the CT sensor having the body 1 which is integrally connected, with the coupling element in a form of a metal plate 12 adapted to be soldered to the copper area 10 of the PCB 11. The body 1 is solid and made of a electrically conductive elastic material, such as silicone. The plate 12 is located in the one body end being the body base 5, and is positioned so the one of its flat surface, being the contact surface 20, is flush mounted in the base 5.

The body 1 is attached to the PCB 11 through soldering of the contact surface 20 of the plate 12 to the copper area 10 on the PCB 11 in the known SMT process during which other electronic components cooperating with the CT sensor are attached to the PCB 11 as well.

It should be noted that the body 1 in this embodiment can have any desired shape, e.g. as shown on Fig. 6, provided that it comprises the flat base 5 connected with the plate 12 as mentioned above. Preferably, the body 1 is cylindrical.

It also should be noted that the plate 12 may extend on the whole surface of the base 5, so the body 1 is electrically connected to the copper area 10 through the plate as shown on Fig. 7.

In order to increase deformability of the solid body 1 of the third embodiment, there can be a recess 30 extending through the plate 12 and into the body 1, as shown on Figs. 10 an 11.

The structure of the CT sensor body 1 according to the third embodiment allows assembling the CT sensor in only one step which is STM process. In view of that the SMT is fully automated soldering process, assembling the CT sensor does not require any additional tools or material above those used in SMT.

Claims

1. A capacitive touch sensor comprising a body (1) made of an electrically conductive elastic material and having a top wall (3) and a base (5) located opposite to the top wall (3) and at least one side wall (4) connecting said top wall (3) with said base (5) wherein said body (1) being mounted on a PCB (11) and the base (5) being electrically connected with a PCB copper area (10) ,

characterized in that it comprises a metal coupling element (2; 12) fixing the body (1) to the PCB (11) and comprising a contact surface (20) adapted to be soldered to the copper area (10) of the PCB (11) , wherein the contact surface (20) is located in the same plane as the outer surface of the body base (5) .

2. The capacitive touch sensor according to claim 1, characterized in that said body (1) is hollow, and the body base (5) comprises an opening (6) which is surrounded by a flange (5a) extending in the plane of the base (5) from the bottom edge of said at least one side wall (4) , said at least one side wall (4) comprises a protrusion (7) extending generally parallel to the body base (5) and inside the body (1) , wherein said coupling element is a clip (2) comprising a base (8) having the contact surface (20) attached to the PCB copper area (10) , and at least one arm (9) extending from the base (8) towards said at least one side wall (4) of the body (1) , wherein the arm (9) contacts the body (1) pressing it towards the PCB (11)

3. The capacitive touch sensor according to claim 2, characterized in that the clip (2) is located in the opening (6) and inside the body (1) so said at least one arm (9) is located between the protrusion (7) and the flange (5a) of the body (1) and contacts the flange (5a) pressing it against the PCB copper area (10) .

4. The capacitive touch sensor according to claim 3, characterized in that said at least one arm (9) is plastically deformable between the free position in which said at least one arm (9) extends at an angle to the clip base (8) and the clamped position in which said at least one arm (9) is generally parallel to the clip base (8) overlapping the clip base flange (5a) .

5. The capacitive touch sensor according to claim 2, characterized in that the clip (2) is located outside the body (1) and surrounds the body (1) , wherein the at least one arm (9) at least partially overlaps and contacts the outer surface of the side wall (4) and the protrusion (7) .

6. The capacitive touch sensor according to claim 1, characterized in that said body (1) is solid and said coupling element is a plate (12) having its contact surface (20) integrally flush mounted in the body base (5) .

7. The capacitive touch sensor according to claim 6, characterized in that the plate (12) extends over the whole outer surface of the body base (5) .

8. The capacitive touch sensor according to claim 6 or 7 , characterized in that there is a central blind opening (30) extending from the contact surface (20) through the plate (12) and the body (1) .

9. The capacitive touch sensor according to any of the preceding claims, characterized in that the body (1) has a cylindrical shape.

10. The capacitive touch sensor according to any of the preceding claims, characterized in that the body (1) is made of the electrically conductive silicone.

11. A method for assembling the capacitive touch sensor, comprising the steps of: providing the capacitive touch sensor according to claims 1-4;

placing the coupling element (2; 12) on the copper area (10) of the PCB (11) and connecting the said coupling element (2; 12) with the copper area (10) in the S T process;

placing the body (1) of capacitive touch sensor aligned with said coupling element (2,12) so said body base (5) contacts the PCB copper area (10) and the arms (9) are placed between the flange (5a) and the protrusion (7) ;

applying a force (15) directed towards the PCB (11) to the top wall (3) of the body (1) and press it against the copper area (10) of the PCB (11) to attach the body to said coupling element (2; 12) and fasten the body (1) to the PCB (11) .