Method and apparatus for intrinsically safe circuit board arrangement for portable electronic devices

Patent metadata

Field	Value
Publication number	US-2016174377-A1
Application number	US-201414571369-A
Country	US
Kind code	A1
Filing date	Dec 16, 2014
Priority date	Dec 16, 2014
Publication date	Jun 16, 2016
Grant date	—

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.

First claim

We claim:

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 se

Assignees

• Motorola Solutions Inc

Inventors

• Chuah Seng Huan
• Bollmann Friedrich Josef
• Choo Khai Jin
• Hor Weng Kong
• Tan Sih Hau

Classifications

• H05K2201/2018

  Presence of a frame in a printed circuit or printed circuit assembly · CPC title

• H05K2201/10409

  Screws · CPC title

• H05K2201/10371

  Shields or metal cases · CPC title

• H05K2201/045

  Hierarchy auxiliary PCB, i.e. more than two levels of hierarchy for daughter PCBs are important · CPC title

• H05K5/064

  sealed by potting, e.g. waterproof resin poured in a rigid casing · CPC title