Low EMI Capacitive Trackpad

• US 20080223628A1
• Filed: 05/30/2008
• Published: 09/18/2008
• Est. Priority Date: 09/24/2004
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Hotelling, Steven P., Lyon, Benjamin
• Granted Patent: US 8,049,736 B2
• Time in Patent Office: Days
• US Class Current: 178/18.01
• CPC Class Codes: G06F 2203/04107 Shielding in digitiser, i.e. guard or shielding arrangements, mostly for capacitive touchscreens, e.g. driven shields, driven grounds
• CPC Class Codes: G06F 2203/04111 Cross over in capacitive digitiser, i.e. details of structures for connecting electrodes of the sensing pattern where the connections cross each other, e.g. bridge structures comprising an insulating layer, or vias through substrate
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes
• CPC Class Codes: H05K 1/0219 Printed shielding conductors for shielding around or between signal conductors, e.g. coplanar or coaxial printed shielding conductors
• CPC Class Codes: H05K 1/11 Printed elements for providing electric connections to or between printed circuits

Abstract

A printed circuit board (PCB) assembly provides a two layer capacitive trackpad sensor in which an EMI ground grid is interposed among the sensor'"'"'s capacitive elements on each of its layers. The EMI grid on each of the two layers is electrically coupled via, typically, vias. The described arrangement of sensor elements (capacitor plates) and EMI ground grid traces may be incorporated into a PCB having additional layers (e.g., a four, six or eight layer PCB). If used in this manner, additional vias are provided on the PCB which permit electrical coupling between these “additional layers” and which are electrically isolated from, and shielded by, the EMI ground grid.

Claims

1. A touch sensor circuit board, comprising a first layer having a first plurality of metal surfaces and a second plurality of metal surfaces electrically isolated from, and interposed between, each pair of the first plurality of metal surfaces, wherein each of the first plurality of metal surfaces are electrically isolated from each other and, further, wherein each of the second plurality of metal surfaces are electrically coupled to each other.

2. The touch sensor circuit board of claim 1, wherein the second plurality of metal surfaces are electrically coupled to a fixed voltage reference.

3. The touch sensor circuit board of claim 2, wherein the fixed voltage reference comprises ground.

4. The touch sensor circuit board of claim 1, further comprising a second layer having a third plurality of metal surfaces that are aligned substantially orthogonal to the first plurality of metal surfaces and a fourth plurality of metal surfaces electrically isolated from, and interposed between, each pair of the third plurality of metal surfaces, wherein each of the third plurality of metal surfaces are electrically isolated from each other and, further, wherein each of the fourth plurality of metal surfaces are electrically coupled to each other.

5. The touch sensor circuit board of claim 4, wherein the second plurality of metal surfaces are electrically coupled to the fourth plurality of metal surfaces.

6. The touch sensor circuit board of claim 5, wherein the second and fourth plurality of metal surfaces are electrically coupled to a fixed voltage reference.

7. The touch sensor circuit board of claim 6, wherein the fixed voltage reference comprises ground.

8. The touch sensor circuit board of claim 4, wherein the second layer further comprises a fifth plurality of metal surfaces that are electrically isolated from the third and fourth plurality of metal surfaces and, further, substantially aligned over the first plurality of metal surfaces.

9. The touch sensor circuit board of claim 1, further comprising two or more additional layers.

10. The touch sensor circuit board of claim 9, further comprising vias for electrically coupling between the two or more additional layers, wherein the vias are electrically isolated from the first and second plurality of metal surfaces and extend through the second plurality of metal surfaces in the first layer and the two or more additional layers.

11. The touch sensor circuit board of claim 1 wherein one or more of the metal surfaces comprise copper metal surfaces.

12. The touch sensor circuit board of claim 4 wherein the first and second layers comprise two sides of a common substrate.

13. The touch sensor circuit board of claim 4 wherein the second and fourth plurality of metal surfaces are electrically coupled.

14. The touch sensor circuit board of claim 4, wherein the first and second layers are separated by a preimpregnated bonding layer material.

15. The touch sensor circuit board of claim 1, wherein each of the first plurality of metal surfaces are electrically coupled to a first electrical circuit for processing touch sensor output signals.

16. The touch sensor circuit board of claim 4, wherein each of the first plurality of metal surfaces are electrically coupled to a first electrical circuit for processing touch sensor output signals and each of the third plurality of metal surfaces are electrically coupled to a second electrical circuit for processing touch sensor output signals.

17. A method to fabricate a touch sensor circuit board, comprising:

forming, on a first surface of a substrate, a first plurality of metal surfaces; and

forming, on the first surface, a second plurality of metal surfaces electrically isolated from, and interposed between, each pair of the first plurality of metal surfaces, wherein each of the first plurality of metal surfaces are electrically isolated from each other and, further, wherein each of the second plurality of metal surfaces are electrically coupled to each other.

18. The method of claim 17, further comprising forming an electrical connection between the second plurality of metal surfaces to an electrical reference.

19. The method of claim 18, wherein the electrical reference comprises a ground.

20. The method of claim 17, further comprising:

forming, on a second surface of the substrate, a third plurality of metal surfaces that are aligned substantially orthogonal to the first plurality of metal surfaces; and

forming, on the second surface, a fourth plurality of metal surfaces electrically isolated from, and interposed between, each pair of the third plurality of metal surfaces, wherein each of the third plurality of metal surfaces are electrically isolated from each other and, further, wherein each of the fourth plurality of metal surfaces are electrically coupled to each other.

21. The method of claim 20, further comprising forming an electrical connection between the second and fourth plurality of metal surfaces.

22. The method of claim 21, further comprising forming an electrical connection between the second plurality of metal surfaces and an electrical reference.

23. The method of claim 22, wherein the electrical reference comprises a ground.

24. The method of claim 20, further comprising forming, on the second surface, a fifth plurality of metal surfaces that are electrically isolated from the third and fourth plurality of metal surfaces and, further, substantially aligned over the first plurality of metal surfaces on the first surface.

25. The method of claim 24, further comprising forming electrical connections between the second plurality of metal surfaces and the fourth plurality of metal surfaces.

26. The method of claim 17, wherein the act of forming the first and second metal surfaces comprises forming said surfaces with copper metal.

27. The method of claim 17, further comprising establishing electrical connections between each of the first plurality of metal surfaces and an electrical circuit for processing touch sensor output signals.

28. The method of claim 24, further comprising:

establishing electrical connections between each of the first plurality of metal surfaces and a first electrical circuit for processing touch sensor output signals; and

establishing electrical connections between each of the third plurality of metal surfaces and a second electrical circuit for processing touch sensor output signals.