GB2382931A

GB2382931A - Means and method of circuit component protection

Info

Publication number: GB2382931A
Application number: GB0228206A
Authority: GB
Inventors: Paul Newman; Edward Stradling
Original assignee: Semikron Ltd
Current assignee: Semikron Ltd
Priority date: 2001-12-05
Filing date: 2002-12-04
Publication date: 2003-06-11
Anticipated expiration: 2022-12-04
Also published as: GB0228206D0; GB0129043D0; GB2382931B

Abstract

Components of a circuit on a printed circuit board 3 are protected from the effects of destructive breakdown of a component or components 1, 2 that is or are likely to undergo destructive breakdown by encasing the component or components 1, 2 in a housing 8. If a heat sink assembly 6 is mounted in contact with a face of the component or components the housing 8 may be arranged to shield the remaining exposed faces of the component or components 1, 2 . The housing 8 may comprise a tray having a base which may be interposed between the component or components 1, 2 and the printed circuit board 3. The housing 8 may be formed from a folded blank of non-flammable material. The housing 8 may also comprise a lid formation.

Description

MEANS FOR AND METI IODS OF CIRCUIT COMPONENT PROTECTION This invention relates to means for and methods of protecting circuits and components associated therewith from the consequences of short circuits occurring in such circuits and components The invention is particularly but not exclusively concerned with the prevention of or at least the reduction of possible damage to a printed circuit board and components mounted thereupon when a component associated with the printed circuit board malfunctions i. e. , short circuits and suffers a catastrophic breakdown and in so doing produces a discharge of carbonaceous material or other debris arising from a catastrophic breakdown of the component It is known to mount components and devices on printed circuit boards such as thyristors which involve rapid pulses of electrical current at the moment of their triggering. It has been found that in the event of an electrical/physical breakdown of such a component occurring, particularly at the time oftnggenng, an explosive reaction occurs which causes the violent discharge of carbonaceous debris which is ejected at high speeds. Such debris has been found to coat or otherwise damage not only the circuits provided upon a printed circuit board but also damage other components provided upon the printed circuit board.

It is an object of the present invention to provide a means whereby the undesirable effects of a breakdown of a circuit component upon associated components and to surrounding parts of apparatus incorporating such a component whether or not it is mounted upon a printed circuit board can be at least minimised..

Broadly according to a first aspect of the invention the invention, there is provided a method of protecting circuit components from the effects of destructive breakdown of a component that is likely to undergo destructive operational

breakdown damage and the consequential production of debris including the step of locating such component in a tailor-made housing which is arranged to shield at least those parts thereof that are exposed and or otherwise in direct contact therewith..

Preferably, when a component that is likely to undergo a destructive breakdown is required to be mounted to a printed circuit board a housing is interposed between the component and the printed circuit board.

In accordance with an aspect of the invention when a heat sink assembly is to be mounted in contacting arrangement with the component such that the heat sink assembly effectively totally covers the adjacent surface of the component the housing is arranged to shield at least the remaining exposed surfaces.

In a preferred arrangement the housing comprises an tray whose base is interposed between the component and the printed circuit board.

Conveniently the housing is formed from a folded blank of non flammable material that is sufficiently stiff as to provide a self-supporting structure after formation.

Preferably where the component mounts in contacting arrangement a heat sink assembly which effectively totally covers a surface of the component the housing is arranged to shield at least the remaining exposed surfaces.

Preferably, when a component that is likely to undergo a destructive breakdown is required to be mounted to a printed circuit board a part of the housing is interposed between the component and the printed circuit board.

Broadly according to a second aspect of the invention a housing for enclosing exposed surfaces of a component mounted to a printed circuit board or other

chassis is formed from rectangular blank of non-inflammable material that is stiff enough after deformation to form the housing.

Preferably the blank is formed from a material known under the trade name Nomex.

In accordance with a further aspect of the invention there is provided a housing for containing effects of destructive breakdown of a component, that is likely to undergo destructive short circuit damage and the consequential production of debris, from damaging apparatus incorporating the component.

Preferably the housing the housing is formed from a folded blank of non flammable material that is stiff sufficiently to provide a self-supporting structure after formation.

In a preferred construction the blank is formed from a material known under the trade name Nomex.

For a better understanding of the invention and to show how to carry the same into effect reference will now be made to accompanying drawing in which :- Figure 1 schematically illustrates as an oblique part cut away representation illustrating the positioning of a short circuiting protection housing of the invention in relation to a component and its associated printed circuit board; Figure 2 schematically illustrates a blank from which the housing of Figure] can be formed and; Figure 3 schematically illustrates the housing blank when folded to form a tray like container.

Referring now to Figure I of the drawings in which components likely to short circuit are schematically shown at I and 2 as being mounted upon a printed circuit board 3. It will be appreciated that the two components could in fact be encapsulated so as to provide a single rectangular block indicated by the dashed line rectangle 4.

It will be appreciated that the components will include contact pins 5 so that the components can be electrically connected on mounting to the printed circuit board to appropriate parts of the circuit (not shown) provided on the printed circuit board. In the Figure these contact pins 5 are indicated as projecting through the printed circuit board 3 In practice, the pins 5 will engage bores in the printed circuit board 3 and will be soldered to the board in such manner that the bores are effectively sealed In Figure] a heat sink 6 is shown mounted to the top of the components 1,2 or 4.

This is conventionally achieved by the use of screws or bolts (not shown) engaging with the module.

The base 7 of a housing 8 having a tray-like formation is interposed between the associated component or components 1,2 or 4 shrouding the ends 9 and sides 10 of the components 1, 2 or 4 in such manner that the components are effectively totally enclosed since the components are covered by the heat sink The housing 8 is formed from a rectangular blank 11 of a stiff foldable non flammable material. The dimensions of the tray are defined in the Figure 2 by fold lines 12,13, 14 and 15. As will be seen four slots 16 are provided in the blank. The slots terminate at the junctions of the fold line pairs 12,13 ; 13, 14 ; 14,15, and

15, 12. These slots 16 effectively define the length of the tray base 7 and the lengths of the side and end walls defined by the parts 17, 18 of the blank To form the tray these side walls 17 are folded about the fold lines to stand perpendicular to the base into the position shown in Figure 3. After which the end walls 18 are folded upwards to stand perpendicular to the base 7 It will be appreciated that the manner of the formation of the blank is such that after the provision of the slots 16 the length of the end walls is such as to provide a flap part 19 at each end thereof. After folding the end walls to the perpendicular position the flap parts 19 are folded to lie against outside of the adjacent the side walls.

The flap parts 19 can be secured to the adjacent side walls by any convenient manner. For example, by a tie (not shown) that circumscribes the side walls and the end walls ; by the shaping of other elements involved by the untt/apparatus with which the components and circuit boald are involved and/or by appropriate non flammable adhesives.

In the formation of the tray it is of considerable importance that the flap parts 19 are located against the outer surfaces of the side walls. It will be appreciated that if the flap parts 19 were to be tucked into the inside of the end walls it could be possible that the force of the component rupture could force out debris between the overlapping flap parts and the end regions of the side will into open space. By arranging the flap parts as shown in the drawings the chances of such dispersal of debris is greatly reduced, if not prevented.

As been mentioned the base 7 of the tray is located against the printed circuit board 3. Bearing in mind that the components enclosed by the tray could require mounting connections with the printed circuit board 3 and connecting pins for effecting electrical connection with the circuitry of the printed circuit board the base of the tray is apertured by suitably positioned holes 20.

The size of these holes 20 is carefully chosen so that the any mounting connections such as pins or screws etc. , the holes sizes are appropriately chosen so that connections and pins are a tight push fit there through It will be seen that the tray effectively produces a debris ejection resistant arrangement which prevents egress of debris through the holes towards the printed circuit board.

Whilst the figure 1 illustrates the mounting of the protected components beneath a heat sink so that the tray is to a great extent covered In, it will be understood that the tray could be provided with a suitable cover so that the tray is effectively totally covered in.

This covering in of the tray could be be by way of a separate cover or could be by incorporating a lid forming part or parts in the blank of Figure 2.

Claims

1. A method of protecting circuit components from the effects of destructive breakdown of a component that is likely to undergo destructive operational breakdown damage and the consequential production of debris including the step of locating such component in a tailor-made housing which is arranged to shield at least those parts thereof that are exposed and or otherwise In direct contact therewith..

2. A method as claimed in claim !, and wherein when a component that is likely to undergo a destructive breakdown is required to be mounted to a printed circuit board a housing is interposed between the component and the printed circuit board.

3. A method as claimed in claim 1 or 2, wherein when a heat sink assembly is to be mounted in contacting arrangement with the component such that the heat sink assembly effectively totally covers the adjacent surface of the component the housing is arranged to shield at least the remaining exposed surfaces.

4. A method as claimed in claim !, 2, or 3, in which the housing comprises an tray whose base is interposed between the component and the printed circuit board.

5. A method as claimed in claim 1, 2,3 or 4, in which the housing is formed from a folded blank of non flammable material that is sufficiently stiff as to provide a self-supporting structure after formation.

6. A method as claimed in claim 3,4 or 5, in which the tray is covered by a lid formation

7 A method as claimed In claim 4 in which the lid formation is separate from the tray.

8. A method as claimed in claim 5 or 6, in which the lid formation is formed from a folded blank serving additionally as a blank from which the tray is folded as the tray.

9 A method as claimed in claim 5,6, 7 or 8, and in which the blank is formed from a material known under the trade name Nomex

10. A method of protecting circuit components from the effects of destructive breakdown of a component that is likely to undergo destructive short circuit damage and the consequential production of debris, substantially as herein before described with reference to the Figures of the accompanying drawmg

11. A housing for containing effects of destructive breakdown of a component, that is likely to undergo destructive short circuit damage and the consequential production of debns, from damaging apparatus incorporating the component.

12. A housing as claimed in claim 10, wherein the housing is formed from a folded blank of non flammable material that is stiff sufficiently to provide a self-supporting structure after formation.

13. A housing as claimed in claim 12, A method as claimed in claim 5, and in which the blank is formed from a material known under the trade name Nomex.

14 A housing for containing effects of destructive breakdown of a component, r that is likely to undergo destructive short circuit damage and the consequential production of debris, from damaging apparatus incorporating the component constructed and arranged to operate substantially as thereinbefore described with reference to Figure 1, 2 or 3 of the accompanying drawing.