Capacitive touch sensor

Abstract

An apparatus includes a circuit board (440) having a first conductive pad (420) on a circuit board surface and a conductive overlay (410B) having a first surface and a second surface opposite the first surface and configured to deflect in response to a touch on the first surface. A protrusion (490) protrudes from the second surface and is configured as a second conductive pad. The circuit board, the conductive overlay, and the protrusion are arranged such that the second surface faces the circuit board surface and is spaced apart from the first conductive pad by a first distance (d1). The protrusion is spaced apart from the first conductive pad by a second distance (d2) and has an overlap region. The apparatus can also include spacers (450A, 450B) configured to space the first conductive pad apart from the second surface by the first distance and to space the protrusion apart from the second surface by the second distance.

Description

BACKGROUND

[0001] Touch sensors continue to replace mechanical devices, such as buttons and switches, as user input into a variety of electronic devices, such as home appliances, vehicles, and point-of-sale terminals. Capacitive touch sensors are often used, some of which are composed of two plates with overlapping areas and separated by a distance. A touch deflects one of the plates, changing the distance between the two plates and, by extension, the capacitance between the two plates. The sensitivity of a capacitive touch sensor depends on the thickness of the plate being touched, i.e., the degree to which it is deflected by the touch, and the distance between the two plates.

[0002] Thinner plates correspond to increased sensitivity, but poor structural strength, such that the sensor can permanently deform and become unusable. In touch-based interfaces, where multiple capacitive touch sensors are in close proximity, a touch on a thinner plate can cause portions of the plates above more than one touch sensor to deflect, causing the interface to incorrectly identify touches at other touch sensors. Thicker plates correspond to better structural strength, but decreased sensitivity, such that a touch on a thicker plate can not deflect the plate and change the capacitance enough to identify the touch. SUMMARY

[0003] An apparatus includes a circuit board having a first conductive pad on a surface of the circuit board and a conductive cover layer having a first cover surface and a second cover surface opposite the first cover surface. The conductive cover layer is configured to deflect in response to a touch on the first cover surface, and a protrusion protrudes from the second cover surface. The protrusion is configured to be a second conductive pad. The circuit board, the conductive cover layer, and the protrusion are arranged such that the second cover surface faces the surface of the circuit board and is separated from the first conductive pad by a first distance. The protrusion is separated from the first conductive pad by a second distance and has an overlapping area.

[0004] In some examples, a surface of the protrusion is substantially planar and parallel to the first conductive pad. The protrusion is cylindrical such that the surface of the protrusion is circular in some examples, and the protrusion is prismatic such that the surface of the protrusion is rectangular in other examples. In some examples, the overlapping area between the first conductive pad and the protrusion is less than an area of the first conductive pad. In some implementations, the conductive cover layer has a first thickness selected such that the conductive cover layer deflects in response to the touch on the first cover surface, and the protrusion has a second thickness selected to be different than the first distance and the second distance. In some examples, the conductive cover layer includes a touch portion, and deflects in response to the touch on the first cover surface at the touch portion. The protrusion protrudes from the second cover surface at a location corresponding to the touch portion.

[0005] In some implementations, the spacer protrudes from the second cover surface at a location outside of the touch portion and has a third thickness selected so that the spacer reduces deflection of the conductive cover layer at the location outside of the touch portion in response to a touch on the first cover surface at the touch portion. In some examples, the spacer contacts the circuit board surface and the third thickness is further selected so that the spacer spaces the first conductive pad from the second cover surface by a first distance and from the protrusion by a second distance. In some implementations, the spacer is a first spacer and the circuit board has a second spacer that contacts the first spacer on the circuit board surface. The second spacer has a fourth thickness selected so that the first and second spacers space the first conductive pad from the second cover surface by the first distance and from the protrusion by the second distance.

[0006] BRIEF DESCRIPTION OF DRAWINGS

[0007] For a detailed description of various examples, refer to the following.

[0008] Figure 1 A capacitor with two plates is shown.

[0009] Figures 2A-2B A schematic diagram and an equivalent circuit diagram of a touch sensor that uses capacitive sensing to detect deflection in the touch sensor are shown.

[0010] Figures 3A-3C Variations of the touch sensor shown in Figure 2A

[0011] Variations of the touch sensor shown in Figures 4A-4C

[0012] Variations of the touch sensor shown in Figure 5

[0013] Variations of the touch sensor shown in Figure 6 DETAILED DESCRIPTION

[0014] The disclosed touch sensor balances touch sensitivity and durability by including a protrusion on the conductive cover layer so that the conductive cover layer is spaced from a conductive sensor pad on a circuit board by a distance that is greater than the distance that the protrusion is spaced from the conductive sensor pad. The smaller the distance between the conductive sensor pad on the circuit board and the protrusion, the higher the touch sensitivity, while the conductive cover layer is spaced from the conductive sensor pad by a larger or sturdier spacer to increase durability. The conductive cover layer can be supported by a spacer on the circuit board, including a second spacer that contacts the spacer on the circuit board, or a spacer that contacts the circuit board itself.

[0015] ​Figure 1 A cross-sectional view of a plate capacitor 100 is shown having an upper plate 110 and a lower plate 120 separated by a distance d. The upper plate 110 and the lower plate 120 can be metal conductive plates and have an overlapping surface area A. In Figure 1 an example, air dielectric 130 separates the upper plate 110 and the lower plate 120, although other dielectric materials are used in other embodiments. The capacitance C of the capacitor 100 can be represented as:

[0016]

[0017] where εr represents the relative permittivity of the dielectric 130 between the upper plate 110 and the lower plate 120, and ε0 represents the permittivity of free space. The capacitance C is inversely proportional to the distance d between the upper plate 110 and the lower plate 120. A change in distance Δd changes the capacitance. Some capacitive touch sensors use the change in distance Δd and the corresponding change in capacitance C to detect a touch.

[0018] Figures 2A-2B A touch sensor 200 and a corresponding equivalent circuit are shown. In Figure 2A the touch sensor 200 includes a conductive plate 210, a sensor pad 220 on a circuit board 240, and spacers 250A-250B on either side of the sensor pad 220 and separating the conductive plate 210 from the sensor pad 220 by a predetermined distance d. The conductive plate 210 and the sensor pad 220 form the upper and lower plates of a capacitor. The conductive plate 210 has an outer planar surface for receiving a touch and an inner planar surface on the opposite side. The sensor pad 220 can be made of copper, such as copper foil or a patterned copper electroplated layer. In one example, the area of the sensor 220 is larger than a fingertip, approximately 100 square millimeters. The distance between the spacers 250A and 250B on either side of the sensor pad 220 can be larger than the area of the sensor 220, which can enable a greater deflection in the conductive plate 210.

[0019] The conductive plate 210 has a selected thickness 260 to allow deflection to occur due to human contact. As Figure 2A shown, the conductive plate 210 deflects in response to pressure applied by a human finger 290 to the conductive plate 210. The deflection results in a change in capacitance proportional to the change in distance Δd. As Figure 2BAs shown, the capacitance of the capacitor formed by conductive plate 210 and sensor pad 220 changes in response to a touch on the outer planar surface of conductive plate 210. By applying a voltage to sensor pad 220, the system can determine the capacitance of the capacitor formed by conductive plate 210 and sensor pad 220. By repeatedly scanning multiple sensors, the system can detect the capacitance change and detect a touch on conductive plate 210 based on the capacitance change.

[0020] The sensitivity of the capacitance of touch sensor 200 to force depends on the thickness 260 of conductive plate 210, the height of spacers 250A-250B, and the resulting distance d. The thickness 260 of conductive plate 210 also affects the durability of touch sensor 200. For example, a conductive plate that is too thin will permanently deform instead of deflecting. Similarly, in a system with multiple touch sensors in close proximity, a too-thin conductive plate and an insufficiently rigid spacer may cause a touch on one sensor to deflect the conductive plate over other sensors, causing them to falsely recognize a touch.

[0021] Figures 3A-3C Illustrated are example touch sensor systems 300A-300C having multiple touch sensors similar to Figure 2A The touch sensor 200 shown in FIG. Figure 3A In FIG, touch sensor system 300A includes a conductive plate or cover layer 310A having a thickness 360A, spacers 350A-350C, and sensor pads 320A-320B on a circuit board 340. Spacers 350A-350C separate conductive plate 310A from sensor pads 320A-320B by a distance dA, which is filled by dielectric 330. Sensor pad 320A forms a first capacitor with conductive plate 310A, which functions as a first touch sensor. Sensor pad 320B forms a second capacitor with conductive plate 310A, which functions as a second touch sensor. Spacer 350B between sensor pads 320A-320B maintains distance dA so that deflection of conductive cover layer 310A over sensor pad 320A does not cause deflection of conductive cover layer 310A over sensor pad 320B, and vice versa, which could cause one of the touch sensors to falsely detect a touch.

[0022] Thickness 360A of conductive plate 310A is greater than thickness 260 of conductive plate 210, so that conductive plate 310A does not deflect as much as conductive plate 210 in response to a touch by a human finger 390. Thickness 360A of conductive cover 310A causes the change in distance ΔdA from the touch of human finger 390 to be very small, so that the corresponding change in capacitance may be less than the threshold value of the capacitance change indicating a touch. Therefore, the greater thickness 360A of conductive cover 310A reduces the sensitivity of touch sensor system 300A.

[0023] In Figure 3B , the touch sensor system 300B is substantially the same as the touch sensor system 300A, but includes a conductive overlay 310B having a thickness 360B that is spaced apart from the sensor pads 320A-B by a distance dB. The thickness 360B of the conductive overlay 310B is less than the thickness 260 of the conductive plate 210 and the thickness 360A of the conductive overlay 310A, such that the conductive overlay 310B deflects more in response to a human finger 390 touch than the conductive plate 210 or the conductive overlay 310A. The thickness 360B of the conductive overlay 310B results in a relatively large change in distance ΔdB from a human finger 390 touch, such that the touch sensor system 300B is more sensitive than the touch sensor system 300A.

[0024] However, the smaller thickness 360B of the conductive overlay 310B corresponds to a weaker structure than the larger thickness 360A of the conductive overlay 310A, such that a touch on the conductive overlay 310B can cause the touch sensor system 300B to deform. The spacers 350B can not be sufficient to maintain the distance dB, such that a deflection of the conductive overlay 310B over the sensor pads 320B also causes a deflection of the conductive overlay 310B over the sensor pads 320A. The deflection over the sensor pads 320A causes the first touch sensor to falsely identify the touch. The smaller thickness 360B can also cause the conductive overlay 310B to remain deformed after a touch is removed compared to its previous position 370. The deformed conductive overlay 310B can remain spaced apart from the sensor pads 320A-B by a distance dB-ΔdB that is less than the distance dB associated with its previous position 370.

[0025] In Figure 3C , the touch sensor system 300C is similar to the touch sensor systems 300A-B, but includes a conductive overlay 310C having a different thickness that is spaced apart from the sensor pads 320A-B by a distance dC that is greater than the distances dA or dB and omitting the spacers 350A-C. The conductive overlay 310C includes its own spacers 382, 384, and 386 with a first thickness 364. The first thickness 364 is selected to space apart the sensor pads 320A-B and the portions of the conductive overlay 310C that are not the spacers 382, 384, and 386 by the distance dC. The spacers 382, 384, and 386 on the conductive overlay 310C are taller and stiffer than the spacers 350A-C to prevent the conductive overlay 310C from deforming as the conductive overlay 310B and falsely identifying touches on other nearby sensor pads.

[0026] The portions of the conductive plate 310C that are not the spacers 382, 384, and 386 have a second thickness 368 that is less than the first thickness 364, and the second thickness 368 is selected to allow deflection to occur due to the touch of the human finger 390. The deflection results in a distance change Adc that can be substantially the same as the distance change Ad for the deflection of the conductive plate 210 compared to the distance d. Although the distance change Ad compared to the distance d results in a change in capacitance sufficient to identify a touch, the distance change Adc compared to the larger distance dC results in a change in capacitance insufficient to identify a touch. Thus, the first thickness 364 of the conductive plate 310C for the spacers 382, 384, and 386 results in a more robust and durable touch sensor system 300C, but also reduces the sensitivity of the touch sensor system 300C such that the human finger 390 must exert more pressure and deflect the conductive overlay 310C more in order to change the capacitance enough to be identified as a touch.

[0027] Figures 4A-4C Example touch sensor systems 400A-400C are illustrated. In Figure 4A The touch sensor system 400A includes a conductive plate or overlay 410A with a protrusion 490 over the sensor pads 420 on a circuit board 440. The conductive plate 410A has a varying thickness and is separated from the sensor pads 420 by a dielectric 430. The conductive plate 410A has a first planar surface that can be touched at a touch portion 415, indicated by the brackets, and a set of internal opposing planar surfaces that face the sensor pads 420 and the circuit board 440. The set of internal surfaces includes a first internal surface that extends from a spacer in a direction that is substantially coplanar with the top of the sensor pads 420 when the conductive overlay 410A is not contacted; a second internal surface that extends perpendicularly from the first internal surface toward the sensor pads 420; a third internal surface that extends from the second internal surface in a direction that is substantially coplanar with the first internal surface when the conductive overlay 410A is not contacted to define the protrusion 490; a fourth internal surface that extends perpendicularly from the third internal surface away from the sensor pads 420; and a fifth internal surface that extends substantially coplanar with the first internal surface when the conductive overlay 410A is not contacted. The first internal surface and the fifth internal surface can meet outside of the illustrated cross-sectional plane. The varying thickness of the conductive overlay 410A allows the touch sensor system 400A to achieve durability and touch isolation while avoiding the corresponding reduction in sensitivity illustrated in the touch sensor system 300C.

[0028] The conductive overlay 410A can have a uniform or varying composition in the protrusion 490 and the remaining portion of the conductive overlay 410. In this regard, the conductive overlay 410A can include any suitable electrically conductive material including metals, electrically conductive polymers, metal impregnated polymers, and combinations thereof that allow the conductive overlay 410A to deflect in response to a touch. In particular, the portion of the conductive overlay 410A having the first thickness 468 deflects and is spaced apart from the sensor pad 420 by a first distance dl in response to a touch on the first planar surface of the conductive overlay 410A. The portions of the conductive overlay 410A having the second thickness 464A act as spacers 482 and 484 and ensure that the portion of the conductive overlay 410A having the first thickness 468 is spaced apart from the sensor pad 420 by the first distance dl in the absence of a touch. The portion of the conductive overlay 410A having the third thickness 470, i.e., the protrusion 490, is spaced apart from the sensor pad 420 by a second distance d2 that is less than the first distance dl. The spacers 482 and 484 of the conductive overlay 410A having the second thickness 464A provide the conductive overlay 410A with a more robust structure associated with the conductive overlay 310C shown in FIG. 3. Figure 3C The protrusion 490 enables the touch sensor system 400A to identify a touch in terms of a distance change Ad that is greater relative to the total distance (e.g., distance d2 compared to the greater distance dl), thereby improving the sensitivity of the touch sensor system 400A relative to the touch sensor system 300C.

[0029] In Figure 4B The touch sensor system 400B is similar to the touch sensor system 400A but includes spacers 450A-450B and a conductive overlay 410B. Like the conductive overlay 410A, a portion of the conductive overlay 410B has a first thickness 468 that deflects, indicated by brackets, and is spaced apart from the sensor pad 420 by a first distance dl in response to a touch on the first planar surface of the conductive overlay 410B at the touch portion 415. Like the conductive overlay 410A, the protrusion 490 on the conductive overlay 410B has a third thickness 470 and is spaced apart from the sensor pad 420 by a second distance d2.

[0030] However, unlike the conductive plate 410A, the portions of the conductive plate 410B that serve as spacers 482 and 484 have a different fourth thickness 464B that is less than the second thickness 464A and greater than the first thickness 468. The spacers 482 and 484 of the conductive plate 410B with the fourth thickness 464B are positioned on top of the spacers 450A-B, respectively, the combination of which ensures that the portions of the conductive overlay 410B with the first thickness 468 are spaced apart from the first sensor pad 420 by the first distance dl. The combination of the spacers 450A-B and the spacers 482 and 484 of the conductive overlay 410B achieves substantially the same durability, touch isolation, and sensitivity as the touch sensor system 400A.

[0031] The spacers 450A-B can be similar or different in material and / or composition from the conductive overlay 410B. In some examples where the material used for the spacers 450A-B is less expensive than the conductive material used for the plate 410B, the combination of the spacers 450A-B and the shallower thickness 464B of the spacers 482 and 484 of the conductive overlay 410B can be selected to reduce manufacturing costs. In other embodiments, the combination is selected to reduce the fragility of the touch sensor system 400B, where the material of the spacers 450A-B is not as hard as the material of the plate 410B, allowing the touch sensor system 400B to bend under high pressure rather than break, but is hard enough to maintain the durability and touch isolation of the system.

[0032] In Figure 4C the touch sensor system 400C is similar to the touch sensor system 400B, but includes a conductive plate 410C. Like the conductive plate 410B, portions of the conductive plate 410C have the first thickness 468, deflect in response to a touch on the first planar surface of the conductive plate 410C at the touch portion 415 (indicated by brackets), and are spaced apart from the sensor pad 420 by the first distance dl. Like the conductive plate 410B, the protrusions 490 on the conductive plate 410C have the third thickness 470 and are spaced apart from the sensor pad 420 by the second distance d2.

[0033] Unlike the conductive electrode plate 410B, however, the conductive electrode plate 410C does not include a portion that functions as a spacer, whether of the second thickness 464A or the fourth thickness 464B. Only the spacers 450A-450B ensure that the portion of the conductive overlay 410C having the first thickness 468 is spaced apart from the sensor pads 420 by the first distance dl. In some examples where the material used for the spacers 450A-450B is less expensive than the conductive material used for the electrode plate 410C, the spacers 482 and 484 can be omitted to reduce manufacturing costs. In other embodiments, the material of the spacers 450A-450B is sufficiently rigid to maintain the durability and contact isolation of the system, including the spacers 482 and 484 on the conductive overlay 410C.

[0034] Figure 5 An inner planar surface of a conductive electrode plate or overlay 500 with a protrusion 590 is illustrated, which can be used as the conductive electrode plates 410A-410C in the touch sensor systems 400A-400C. The conductive electrode plate 500 has a first thickness 568 in a region 520, which is configured to deflect in response to a touch. The conductive overlay 500 has a second thickness 564 in a region 580, which functions as a spacer. The conductive overlay 500 has a third thickness 570 at the protrusion 590. Although in this example, the protrusion 590 is shown as being substantially centered in the region 520, in other embodiments, the protrusion 590 is not centered in the region 520. A surface 595 of the protrusion 590 is configured to be placed facing a corresponding sensor pad, such that the surface 595 and the corresponding sensor pad have an overlapping region. The overlapping region can be less than the surface area of the respective sensor pad. In some embodiments, the overlapping region is substantially centered over the respective sensor pad, while in other embodiments the overlapping region is not centered over the respective sensor pad.

[0035] The surface 595 is spaced apart from the respective sensor pad by a distance that is less than the distance by which the region 520 is spaced apart. Although the protrusion 590 is shown as being cylindrical and the surface 595 is shown as having a circular shape, any appropriate shape can be used to obtain the desired shared surface area between the surface 595 and the respective sensor pad, so long as the surface 595 is flat, rather than pointed or rounded. In some embodiments, the protrusion 590 is prismatic, such that the surface 595 is rectangular.

[0036] Figure 6An example process 600 for detecting a touch on a touch sensor, such as the touch sensor systems 400A-400C, is illustrated. The process 600 is configured to be performed by one or more processing units capable of reading from and / or writing to an appropriate non-transitory storage medium, such as static random access memory (SRAM). The storage medium can be used for storing instructions and data received from the one or more processing units. For step 610, and at a first time, the processing unit determines a first capacitance between a surface of a protrusion on a conductive pad and a conductive sensor on a circuit board, the conductive sensor on the circuit board being separated from the surface of the protrusion by a distance. For example, the processing unit determines a first capacitance between the surface of the protrusion 490 and the sensor pad 420 in any of the touch sensor systems 400A-400C, which are separated by the distance d2.

[0037] For step 620 and at a subsequent time, the processing unit determines a subsequent capacitance between the surface of the protrusion and the conductive sensor. At step 630, the processing unit compares the first capacitance and the subsequent capacitance. At step 640, if the processing unit determines that the change in capacitance between the first capacitance and the subsequent capacitance is not greater than a threshold change in capacitance, the processing unit proceeds to step 650. The threshold change in capacitance can be selected to represent a change in capacitance due to a touch on the conductive pad that reduces the distance between the surface of the protrusion and the conductive sensor. At step 650, the processing unit stores the subsequent capacitance as the first capacitance and continues to repeat steps 620-640.

[0038] At step 640, if the processing unit determines that the change in capacitance between the first capacitance and the subsequent capacitance is greater than the threshold change in capacitance, the processing unit outputs a notification indicating a touch on the conductive pad with sufficient pressure to reduce the distance between the surface of the protrusion and the conductive sensor such that the resulting change in capacitance is greater than the threshold change in capacitance. That is, the processing unit outputs a notification indicating a touch on the touch sensor.

[0039] The term“coupled” is used throughout the specification. This term can encompass a connection, a communication, or a signal path in a manner consistent with the description of the present disclosure. For example, if device A generates a signal to control device B to perform an action, then in a first example, device A is coupled to device B, or in a second example, device A is coupled to device B through an intermediate component C that does not materially change the functional relationship between device A and device B such that device B is controlled by device A via the control signal generated by device A.

Claims

1. An apparatus comprising: a circuit board having a first conductive pad on a circuit board surface; and a conductive cover layer having: - a first cover surface; - a second cover surface opposite the first cover surface, such that the conductive cover layer has a first thickness between the first cover surface and the second cover surface; and - a protrusion protruding from the second cover surface and having a third cover surface, such that the conductive cover layer has a second thickness between the first cover surface and the third cover surface that is greater than the first thickness, wherein the conductive cover layer is configured to deflect in response to a touch on the first cover surface; and wherein the circuit board, the conductive cover layer, and the protrusion are arranged such that: - the second cover surface faces the circuit board surface, - the second cover surface and the first conductive pad are separated by a first distance, and - the protrusion and the first conductive pad are separated by a second distance, the protrusion and the first conductive pad having an overlapping area.

2. The apparatus of claim 1, wherein the first thickness of the conductive cover layer is such that the conductive cover layer is configured to deflect in response to a touch on the first cover surface, and the difference between the first thickness and the second thickness of the conductive cover layer is equal to the difference between the first distance and the second distance.

3. The apparatus of claim 1, wherein the conductive cover layer includes a touch portion, wherein the conductive cover layer is configured to deflect in response to the touch on the first cover surface at the touch portion, and wherein the protrusion protrudes from the second cover surface at a location corresponding to the touch portion.

4. The apparatus of claim 3, wherein the protrusion protrudes from the second cover surface at a location substantially centered in the touch portion.

5. The apparatus of claim 3, further comprising a spacer protruding from the second cover surface at a location outside the touch portion.

6. The apparatus of claim 5, wherein the spacer has a third thickness such that the spacer reduces deflection of the conductive cover layer at a location outside the touch portion in response to a touch on the first cover surface at the touch portion.

7. The apparatus of claim 6, wherein the spacer physically contacts the circuit board surface, wherein the third thickness causes the spacer to separate the second cover surface and the first conductive pad by the first distance and to separate the protrusion and the first conductive pad by the second distance. ​ 8. The apparatus of claim 6, wherein the spacer comprises a first spacer, the circuit board further having a second spacer on the circuit board surface, the second spacer physically contacting the first spacer and having a fourth thickness, such that the first and second spacers separate the second covering surface and the first conductive pad by the first distance and separate the protrusion and the first conductive pad by the second distance.

9. The apparatus of claim 3, the circuit board further having a spacer on the circuit board surface, the spacer physically contacting the second covering surface at a location outside the touch portion and having a fifth thickness, such that the spacer separates the second covering surface and the first conductive pad by the first distance and separates the protrusion and the first conductive pad by the second distance.

10. The apparatus of claim 1, wherein a third covering surface of the protrusion is substantially flat and parallel to the first conductive pad.

11. The apparatus of claim 10, wherein the protrusion is cylindrical, such that the third covering surface of the protrusion is circular.

12. The apparatus of claim 10, wherein the protrusion is prismatic, such that the third covering surface of the protrusion is rectangular.

13. The apparatus of claim 1, wherein the overlap region comprises an area smaller than the first conductive pad.

14. An apparatus comprising: a circuit board having a first conductive sensor pad on a circuit board surface; a conductive cover layer having: - a first covering surface; - a second covering surface opposite the first covering surface, such that the conductive cover layer has a first thickness between the first and second covering surfaces; - a protrusion protruding from the second covering surface and having a protrusion surface that is flat and parallel to the second covering surface, the protrusion having a second thickness between the first covering surface and the protrusion surface that is larger than the first thickness, wherein the protrusion is configured to function as a second conductive sensor pad; and - a touch portion comprising the second covering surface and a portion of the protrusion, wherein the protrusion is substantially centered in the touch portion, and wherein the touch portion is configured to deflect in response to a touch on the first covering surface at the touch portion; and a spacer protruding from the second covering surface at a location outside the touch portion and having a third thickness selected such that the spacer is configured to reduce deflection of the conductive cover layer at the location outside the touch portion in response to a touch on the first covering surface at the touch portion, wherein the circuit board, the conductive cover layer, and the protrusion are arranged such that: - the second covering surface faces the circuit board surface, - the second covering surface and the first conductive sensor pad are separated by a first distance, such that the second thickness causes the protrusion surface and the first conductive sensor pad to be separated by a second distance, and - the protrusion surface and the first conductive sensor pad have an overlap area.

15. The apparatus of claim 14, wherein the overlap area is not centered over the first conductive sensor pad.

16. The apparatus of claim 14, wherein the overlap area comprises less area than the first conductive sensor pad.

17. The apparatus of claim 14, wherein the spacer physically contacts the circuit board surface, and wherein the third thickness causes the spacer to separate the second covering surface and the first conductive sensor pad by the first distance.

18. The apparatus of claim 14, wherein the spacer comprises a first spacer, the circuit board further having a second spacer on the circuit board surface, the second spacer physically contacting the first spacer and having a fourth thickness, such that the first and second spacers separate the second covering surface and the first conductive sensor pad by the first distance.

19. An apparatus comprising: a circuit board; a first capacitor plate disposed on the circuit board; a set of spacers disposed on the circuit board alongside the first capacitor plate; and a conductive covering layer disposed on the set of spacers, wherein the conductive covering layer comprises: - an outer surface disposed away from the first capacitor plate; - a first inner surface disposed toward the first capacitor plate, wherein the conductive covering layer has a first thickness between the outer surface and the first inner surface; and the first inner surface is separated from the first capacitor plate by a first distance in an uncontacted configuration; and - a second inner surface disposed toward the first capacitor plate, wherein: the conductive covering layer has a second thickness between the outer surface and the second inner surface that is greater than the first thickness; the second inner surface is separated from the first capacitor plate by a second distance in the uncontacted configuration; and the second distance is less than the first distance.

20. The apparatus of claim 19, wherein the conductive covering layer further comprises a third inner surface that extends from the first inner surface to the second inner surface in a direction substantially perpendicular to the first capacitor plate in the uncontacted configuration.

21. The apparatus of claim 20, wherein the first inner surface extends along a top surface of a first spacer of the set of spacers, such that the first inner surface is substantially co-planar along the top surface of the first spacer and from the first spacer to the third inner surface in the uncontacted configuration. ​ 22. The device of claim 19, wherein the electrically conductive cover layer has a substantially uniform composition between the outer surface and the first inner surface and between the outer surface and the second inner surface.

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