Method and apparatus for providing backlighting for keypads and LCD panels

• US 5,708,428 A
• Filed: 12/10/1996
• Issued: 01/13/1998
• Est. Priority Date: 12/10/1996
• Status: Expired due to Term

• Current Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Phillips, John Charles
• Primary Examiner(s): Hofsass, Jeffery
• Assistant Examiner(s): Edwards, Jr., Timothy
• Application Number:
  US08/761,327
• Time in Patent Office: 399 Days
• Field of Search: 200/54, 200/314, 340/815.45, 340/815.55, 340/815.73, 340/815.42, 340/815.49, 340/825.82, 379/368, 379/369, 379/370, 379/433, 341/22, 345/170, 345/173, 345/176
• US Class Current: 341/22
• CPC Class Codes: H01H 13/702 with contacts carried by or formed from layers in a multilayer structure, e.g. membrane switches
• CPC Class Codes: H01H 2207/026 Pressure contact
• CPC Class Codes: H01H 2209/082 transparent
• CPC Class Codes: H01H 2219/014 LED
• CPC Class Codes: H01H 2219/04 Attachments; Connections
• CPC Class Codes: H01H 2229/048 Insertion moulding
• CPC Class Codes: H01H 2231/022 Telephone handset
• CPC Class Codes: H01H 2239/014 on both sides
• CPC Class Codes: H04M 1/22 Illumination; Arrangements for improving the visibility of characters on dials

Abstract

Light-emitting diodes are embedded, preferably by insert molding, directly into the translucent elastomeric material forming a keypad or surrounding structure adjacent the light guide of a liquid crystal display panel. The electrical contacts of the LEDs are maintained in bias contact with contact pads provided on the secondary surface of a printed circuit board. The bias contact is preferably provided by a cover assembly which provides a compressive force against the elastomeric keypad when assembled with the printed circuit board and keypad. The present invention enables the construction of a printed circuit board having all of the electrical components disposed on only the primary side of the board, thereby permitting a simpler layout of the electrical circuitry on the PCB and the construction of a thinner keyboard assembly.

Claims

1. A keyboard assembly, comprising:

a keypad formed of a translucent elastomeric material;

a light-emitting diode embedded within said translucent elastomeric material of the keypad and having a pair of electrical contacts not covered by said translucent elastomeric material;

a printed circuit board having a pair of electrical contacts disposed on a secondary surface of the board in alignment with said pair of electrical contacts of the light-emitting diode when said keypad is assembled with said printed circuit board; and

means for providing a bias force urging said light-emitting diode embedded in said elastomeric material in a direction toward said secondary surface of the printed circuit board when said keypad and said printed circuit board are assembled together and maintain the electrical contacts of the light-emitting diode in electrical communication with the electrical contacts disposed on the secondary surface of the printed circuit board.

2. A keyboard assembly, as set forth in claim 1, wherein said means for providing a bias force includes a cover assembleable with said keypad and said printed circuit board.

3. A keyboard assembly, as set forth in claim 1, wherein said translucent elastomeric material is silicone rubber.

4. A keyboard assembly, as set forth in claim 1, wherein said secondary side of the printed circuit board includes only electrical contacts and said printed circuit board has a primary side on which electrical components are mounted.

5. A keyboard assembly, as set forth in claim 1, wherein said light-emitting diode is insert-molded in said translucent elastomeric material.

6. A keyboard assembly, as set forth in claim 1, wherein said keyboard assembly is adapted for use in a cellular telephone.

7. A keyboard assembly, as set forth in claim 1, wherein said assembly includes a liquid crystal display panel disposed adjacent said translucent elastomeric keypad, a light guide adapted to direct light to a backside of the liquid crystal display panel, and an additional light-emitting diode embedded in said translucent elastomeric keypad at a position adjacent said light guide.

8. A keyboard assembly, as set forth in claim 2, wherein said additional light-emitting diode emits light through a side of the diode.

9. A keyboard assembly, comprising:

a liquid crystal display panel having a light guide adapted to direct light to a backside of the liquid crystal display panel;

an elastomeric member formed of a translucent material and extending along at least one side of said liquid crystal display panel;

a light-emitting diode embedded in said elastomeric member at a position adjacent said light guide in light-transmitting communication with said light guide of the liquid crystal display panel and having a pair of electrical contacts not covered by said elastomeric member; and

a printed circuit board having a pair of contacts disposed on a secondary surface in alignment with said pair of contacts of said light-emitting diode when said liquid crystal display panel is assembled with said printed circuit board, and a cover assembleable with said liquid crystal display panel, said elastomeric member and said printed circuit board and adapted to provide a bias force urging said light-emitting diode embedded in said elastomeric member in a direction toward said secondary surface of the printed circuit board when said cover, said liquid crystal display panel, said elastomeric member and said printed circuit board are assembled together, and maintain the electrical contacts of the light-emitting diode in electrical communication with the electrical contacts disposed on the secondary surface of the printed circuit board.

10. A keyboard assembly, as set forth in claim 9, wherein said light-emitting diode emits light through a side of the diode.

11. A keyboard assembly, as set forth in claim 9, wherein said secondary side of the printed circuit board includes only electrical contacts and said printed circuit board has a primary side on which electrical components are mounted.

12. A keyboard assembly, as set forth in claim 9, wherein said keyboard assembly is adapted for use in a cellular telephone.

13. A keyboard assembly, as set forth in claim 9, wherein said assembly includes a keypad formed of a translucent elastomeric material and said elastomeric member extending along at least one side of said liquid crystal display panel comprises an integrally-formed portion of the keypad.

14. A keyboard assembly, as set forth in claim 13, wherein said light-emitting diode is insert-molded in said keypad.

15. A keyboard assembly, comprising:

a keypad having a plurality of keys disposed on an upper surface and a lower surface spaced from said upper surface, said keypad being formed of a translucent elastomeric material;

a light guide disposed adjacent said lower surface of the keypad, said light guide being formed of a light-transmitting material;

a light-emitting diode embedded within said light guide and having a pair of electrical contacts not covered by said light-transmitting material of the light guide;

a printed circuit board having a pair of electrical contacts disposed on a secondary surface of the board in alignment with said pair of electrical contacts of the light-emitting diode when said light guide is assembled with said printed circuit board; and

a means for providing a bias force urging said light-emitting diode embedded in said light guide in a direction toward said secondary surface of the printed circuit board when said keypad, said light guide and said printed circuit board are assembled together and maintain the electrical contacts of the light-emitting diode in electrical communication with the electrical contacts disposed on the secondary surface of the printed circuit board.

16. A keyboard assembly, as set forth in claim 15, wherein said means for providing a bias force includes a cover assembleable with said keypad, said light guide, and said printed circuit board.

17. A keyboard assembly, as set forth in claim 15, wherein said light guide is formed of a substantially rigid polymer material.

18. A keyboard assembly, as set forth in claim 15, wherein said light-emitting diode is insert-molded in said light guide.

19. A method of forming a keyboard assembly, comprising:

inserting a light-emitting diode having a pair of electrical contacts into a predefined position in a mold;

closing said mold to form a defined mold cavity;

inserting a liquefied elastomeric material into said mold cavity whereby said light-emitting diode is substantially embedded in said elastomeric material;

at least partially curing said elastomeric material and thereby forming a keypad having a light-emitting diode embedded therein;

removing said formed keypad from said mold cavity;

providing a printed circuit board having a secondary surface with a pair of electrical contacts provided thereon;

providing a cover;

assembling said printed circuit board and said molded keypad together with said cover whereby said electrical contacts of said light-emitting diode is maintained in biased contact with said electrical contacts of said printed circuit board.

20. A method of forming a keyboard assembly, as set forth in claim 19, wherein said elastomeric material is a translucent silicone rubber compound.

21. A method of forming a keyboard assembly, as set forth in claim 19, wherein said light-emitting diode emits light in a vertical direction with respect to said electrical contacts of the diode.

22. A method of forming a keyboard assembly, as set forth in claim 19, wherein said light-emitting diode emits light in an orthogonal direction with respect to said electrical contacts of the diode.

23. A method of forming a keyboard assembly, as set forth in claim 19, wherein said inserting a liquefied elastomeric material into said mold cavity includes injecting said liquefied elastomeric material, under pressure, into said mold cavity.

24. A method of forming a keyboard assembly, as set forth in claim 19, wherein said keyboard assembly is adapted for use in a cellular telephone.