METHOD AND APPARATUS FOR INTRINSICALLY SAFE CIRCUIT BOARD ARRANGEMENT FOR PORTABLE ELECTRONIC DEVICES

• US 20160174377A1
• Filed: 12/16/2014
• Published: 06/16/2016
• Est. Priority Date: 12/16/2014
• Status: Active Grant

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola Solutions, Inc.
• Inventors: CHUAH, SENG HUAN, BOLLMANN, FRIEDRICH JOSEF, CHOO, KHAI JIN, TAN, SIH HAU, HOR, WENG KONG
• Granted Patent: US 9,980,381 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H04M 1/0277 for a printed circuit board assembly
• CPC Class Codes: H05K 1/0215 Grounding of printed circuits by connection to external grounding means
• CPC Class Codes: H05K 1/0224 Patterned shielding planes, ground planes or power planes H05K1/0253 takes precedence
• CPC Class Codes: H05K 1/14 Structural association of two or more printed circuits providing electric connection to or between printed circuits H05K1/11, H01R12/00
• CPC Class Codes: H05K 1/144 Stacked arrangements of planar printed circuit boards
• CPC Class Codes: H05K 2201/041 Stacked PCBs, i.e. having neither an empty space nor mounted components in between
• CPC Class Codes: H05K 2201/042 Stacked spaced PCBs; Planar parts of folded flexible circuits having mounted components in between or spaced from each other
• CPC Class Codes: H05K 2201/043 Stacked PCBs with their backs attached to each other without electrical connection
• CPC Class Codes: H05K 2201/045 Hierarchy auxiliary PCB, i.e. more than two levels of hierarchy for daughter PCBs are important
• CPC Class Codes: H05K 2201/10371 Shields or metal cases
• CPC Class Codes: H05K 2201/10409 Screws
• CPC Class Codes: H05K 2201/2018 Presence of a frame in a printed circuit or printed circuit assembly
• CPC Class Codes: H05K 5/064 sealed by potting, e.g. waterproof resin poured in a rigid casing

Abstract

A method and circuit board arrangement for an intrinsically safe portable device includes two or more circuit boards having a frame structure that forms a contiguous boundary around a space between the circuit boards. In the space there are circuit components mounted on both circuit boards, and a connector that connect the two circuit boards. An encapsulant material fills the space bounded by the frame structure between the circuit boards to exclude airborne material from coming into contact with the encapsulated circuit components.

Claims

1. An intrinsically safe circuit board arrangement for a portable two-way radio device, comprising:

a first circuit board having a plurality of circuit components disposed on a top surface of the first circuit board;

a frame structure mounted on the top surface of the first circuit board that is contiguous around the plurality of circuit components on the top surface of the first circuit board and defines a space bounded by the frame structure in which the circuit components of the first circuit board are disposed;

a second circuit board positioned over the first circuit board mounted on top of the frame structure and having a plurality of circuit components disposed on a bottom surface of the second circuit board within the space bounded by the frame structure;

a connector in the space bounded by the frame structure that electrically connects the first circuit board to the second circuit board; and

an encapsulant material that fills the volume bounded by the frame structure between the first and second circuit boards that exclude gas from the volume bounded by the frame structure.

2. The intrinsically safe circuit board arrangement of claim 1, wherein the frame structure comprises an electrically conductive frame member.

3. The intrinsically safe circuit board arrangement of claim 2, wherein the electrically conductive frame member is attached to the first and second circuit boards with conductive adhesive.

4. The intrinsically safe circuit board arrangement of claim 3, wherein the conductive adhesive between the first circuit board and the electrically conductive frame member electrically connects a ground plane of the first circuit board to the electrically conductive frame member, and the conductive adhesive between the second circuit board and the electrically conductive frame member electrically connects a ground plane of the second circuit board to the electrically conductive frame member.

5. The intrinsically safe circuit board arrangement of claim 1, further comprising fasteners that traverse through the first and second circuit boards and the frame structure.

6. The intrinsically safe circuit board arrangement of claim 5, wherein the fasteners are screw-type fasteners.

7. The intrinsically safe circuit board arrangement of claim 1, further comprising a seal member that surrounds the connector and excludes the encapsulant material from the connector.

8. The intrinsically safe circuit board arrangement of claim 1, wherein the frame structure is a first frame structure, the intrinsically safe circuit board arrangement further comprises:

a plurality of circuit components on a top surface of the second circuit board;

a second frame structure mounted on the top surface of the second circuit board that is contiguous around the plurality of circuit components on the top surface of the second circuit board and defines a space bounded by the second frame structure in which the circuit components on top of the second circuit board are disposed;

a third circuit board positioned over the second circuit board mounted on top of the second frame structure and having a plurality of circuit components disposed on a bottom surface of the third circuit board within the space bounded by the second frame structure;

a connector in the space bounded by the second frame structure that electrically connects the second circuit board to the third circuit board; and

an encapsulant material that fills the volume bounded by the second frame structure between the second and third circuit boards that exclude gas from the volume bounded by the second frame structure.

9. A method of forming an intrinsically safe circuit board arrangement for a portable electronic device, comprising:

arranging a frame structure between a first circuit board and a second circuit board, wherein the frame structure provides a contiguous boundary around a space between the first and second circuit boards, the first and second circuit boards having circuit components and a connector between the first and second circuit boards located within the space bounded by the frame structure;

injecting an encapsulant material into, and filling the space bounded by the frame structure between the first and second circuit boards; and

curing the encapsulant material.

10. The method of claim 9, further comprising assembling the circuit board arrangement into a housing of a portable radio communication device.

11. The method of claim 9, wherein injecting the encapsulant material comprises injecting the encapsulant materials through an injection port in one of the first or second circuit boards, wherein the one of the first or second circuit boards having the injection port further include a vent port to allow air in the space bounded by the frame structure between the first and second circuit board to escape as the encapsulant material is being injected.

12. The method of claim 9, wherein the frame structure is a first frame structure, the method further comprises:

arranging a second frame structure between the second circuit board and third circuit board; and

injecting encapsulant material into a space bounded by the second frame structure between the second and third circuit boards.

13. The method of claim 9, wherein arranging the frame structure comprises placing a first adhesive layer between a frame member of the frame structure and the first circuit board and a second adhesive layer between the frame member and the second circuit board.

14. An intrinsically safe portable radio communication device, comprising:

a housing;

a circuit board arrangement disposed in the housing comprising;

a first circuit board having a top surface with a frame structure mounted on the top surface of the first circuit board that is contiguous around a plurality of circuit components on the top surface of the first circuit board, and a second circuit board positioned over the first circuit board mounted on top of the frame structure and having a plurality of circuit components disposed on a bottom surface of the second circuit board within a space bounded by the frame structure between the first and second circuit board;

a connector in the space bounded by the frame structure that electrically connects the first circuit board to the second circuit board; and

an encapsulant material that fills the space bounded by the frame structure between the first and second circuit boards which exclude airborne material from the space bounded by the frame structure.

15. The intrinsically safe portable radio communication device of claim 14, wherein the frame structure comprises an electrically conductive frame member.

16. The intrinsically safe portable radio communication device of claim 15, wherein the electrically conductive frame member is attached to the first and second circuit boards with conductive adhesive.

17. The intrinsically safe portable radio communication device of claim 16, wherein the conductive adhesive between the first circuit board and the electrically conductive frame member electrically connects a ground plane of the first circuit board to the electrically conductive frame member, and the conductive adhesive between the second circuit board and the electrically conductive frame member electrically connects a ground plane of the second circuit board to the electrically conductive frame member.

18. The intrinsically safe portable radio communication device of claim 14, further comprising fasteners that traverse through the first and second circuit boards and the frame structure.

19. The intrinsically safe portable radio communication device of claim 18, wherein the fasteners are screw-type fasteners.

20. The intrinsically safe portable radio communication device of claim 14, further comprising a seal member that surrounds the connector and excludes the encapsulant material from the connector.