GB2203903A - Sealed lead-through terminations - Google Patents

Abstract

A means of sealing the electrical terminations (12, 14) of a component (10), such as an LED, to a surrounding tubular body (18), wherein the terminations (12, 14) extend through an elastomeric member (36) which is arranged to be sandwiched in a permanently compressed condition between a pair of pressure pads (32, 34) such that the elastomeric member (36) effects sealing both with the inner periphery of the tubular body (18) and with the terminations (12, 14). Compression is achieved by peening the end (40) of the body (18) or by inserting a plug (42) into the body (18). <IMAGE>

Description

DESCRIPTION SEALED LEAD-THROUGH TERMINATIONS.

The present invention is concerned with terminations to electronic components of the type which are required to be sealed to the body of the electronic component in addition to provide the necessary insulated electrical lead-through.

Conventional techniques typically use plastics potting compounds or the terminations are formed as inserts in a plastics moulding. Due to the inevitable thermal mismatch between the components, these techniques suffer from thermal stresses which often have a deleterious effect on the integrity of the seal, particularly in severe climatic conditions. In addition, plastics of this kind can themselves be permeable to moisture. Cast resins in particular are difficult to apply consistently and their application is constrained by gravity.

Conventional hermetic lead-throughs are traditionally made of glass/ceramic to metal seals and whilst their use is widespread in electronics, they are expensive and liable to damage due to the brittle nature of the glass or ceramic used. The metal parts of a glass ceramic lead-through have also to be thermally matched to the glass or ceramic and this can substantialiy constrain the component design and increase costs.

Conventional O-ring seals can also be used to provide lead-through seals but they require clean smooth O-ring grooves with accurate dimensions to effect a good seal and particularly in miniature designs this is a severe constraint.

It is an object of the present invention to substantially improve on the existing sealing techniques.

In accordance with the present invention, there is provided a means of sealing the electrical terminations of a component, such as a lamp, to a surrounding tubular body, wherein the terminations extend through an elastomeric member which is arranged to be sandwiched in a permanently pressurized condition between a pair of pressure pads, such that the elastomeric member effects sealing both with the inner periphery of the tubular body and with said terminations.

In one preferred embodiment the elastomeric body, for example of silicone rubber or fluorocarbon rubber, is in the form of a disc pierced with one or more, preferably two or more holes for receiving the terminations therethrough; the two pressure pads also have through-holes so that the terminations can be inserted through the holes in the pressure pads/elastomeric body sandwich and the whole constrained within the tubular body in a manner such as to maintain the compressed condition of the elastomer.

Normally, the pressure pads and the elastomer would have electrically insulating characteristics so as to isolate the terminations from each other and from the surrounding tubular body.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Fig.l is a longitudinal cross-sectional view of one embodiment of a panel-mounted LED embodying the present invention; and Figs.2, 3, 4 and 5 are longitudinal crosssectional views of second, third, fourth and fifth embodiments, respectively.

Referring to Fig.l, an LED indicator light 10 with electrical wire terminations 12 and 14 is housed within one end of a generally cylindrical cavity 16 in an externally screw-threaded body 18, the base of the LED being located on a shoulder 20 on the inner wall of the body defining the cavity 16. This one end of the body 18 is closed by a disc-like lens 22 which is held in place above the LED 10 by an annular screw-threaded bezel 24, an 0being seal 26 being disposed between the lens 22 and the body 18. The body 18 carries a radial flange 28 to enable the body to be secured, in use, in a panel aperture by means of a lock-nut (not shown) carried by external screwthreads 30 on the body.

The two wire terminations 12,14 to the light 10 extend out of the other end of the body 18 and are sealed to the body 18 by means of an elastomeric disc 36 which is arranged to be compressed between a pair of rigid pressure pads 32,34. The pressure pads 32,34 and the elastomeric disc 36 have aligned holes therethrough for receiving the terminations 12,14, the inner pressure pad engaging a further internal shoulder 38 on the body 18 so that the elastomeric disc 36 can be subjected to compressive pressure by exerting a force on the other pressure pad 34 in a direction towards the pad 32. With the elastomeric disc 36 subjected to compression in this manner, the pad 34 is then arranged to be held in place in the body 18 so as to maintain the compression permanently in the disc 36.

In the embodiment of Fig.l, retention of the pressure pad 34 in the body 18 is achieved by peening over the end circumference of the body 18 as shown at 40, while the elastomer 36 is held under compression.

In the al,ernative embodiment shown in Fig.2, the retention of the pad 34 is achieved by the use of an interference-fitting end plug 42 having annular frusto-conical protrusions 44 on its peripheral surface which engage with similarly-shaped protrusions 46 on the inner wall of the body in order to maintain the required position of the pressure pad 34.

Other means of retention could equally well be used, such as a screwed cap or ring.

A particular feature of the above-described arrangement is that a force on the pressure pad/elastomer assembly from either direction is transmitted to the elastomer 36 which, being effectively incompressible, transmits the pressure to the sealing interfaces between the inside of the body cavity and the elastomer and between the elastomer and the wire terminations 12,14 to thereby improve the effectiveness of the seal.

Constrained and pressured in this way, the seal effected by the elastomeric disc 18 is extremely resilient to thermal cycling and mechanical stresses.

In addition, the above-described configuration assists considerably in assembly operations as it is substantially self-jigging and, with the pressure pads 32,34 manufactured in a rigid electrically insulating material, such as glass-loaded nylon or a'phenolic, the necessary electrical insulation of the lead-through terminations 12,14 is conveniently integral with the sealing mechanism.

Referring now to Fig.3, there is shown a slightly modified embodiment which is essentially the same as that of Fig.l except that the position of the internal shoulder 38 of the Fig.l embodiment has been moved to 38a in Fig.3 so that the flange on the LED 10 bears against it when the elastomer 36 is pressurised. By this means, in addition to effecting a rear seal, the LED is clamped in place by the pressure. Assembly of the LED in the body 18 is then advantageously from only one end of the body (the rear end). A further practical advantage is that this means that the O-ring seal 26 can then be made and tested prior t6 insertion of the LED. Furthermore, the lens seal could in this case be a hermetic or solder seal of the type which involve high temperatures in their manufacture (which would in other arrangements damage the LED and therefore be unusable).

In the modified embodiment of Fig.4, the internal body shoulder 38 is dispensed with altogether and the pressure providing the rear seal is transmitted by means of a tube 50 to the front lens seal so that both the front and the rear seal and the assembly of the LED can be affected in the one operation.

Returning now to the structure and operation of the elastomer 36 sandwiched between the two pressure pads 32,34, when the elastomer 36 is under pressure and the ambient temperature is higher than the temperature at which the pressure was applied, the elastomer (which usually has a temperature coefficient of expansion larger than that of the metal body 18 and the leads 12,14) will provide an improved seal.

However, when the temperature is lower than the temperature at which the pressure was applied, the elastomer will generally contract and this may reduce the sealing action between the elastomer and the internal surfaces of the body 18. In order to counteract this effect, the pressure pads 32,34 can advantageously be formed with recesses 52,54,56 asshown in Fig.5 so that, under pressure, the disc-shaped elastomer is distorted into the spaces provided by these recesses in the pads. When the elastomer then suffers differential contraction with respect to the body 18 and the leads 12,14, the forces urging it to return to its original shape ensure that a sealing pressure is retained at the body or lead/ elastometer interfaces.

Claims (1)

1. A sealing arrangement for sealing the electrical terminations of a component, such as a lamp, to a surrounding tubular body, wherein the terminations extend through an elastomeric member which is arranged to be sandwiched in a permanently pressurized condition between a pair of pressure pads, such that the elastomeric member effects sealing both with the inner periphery of the tubular body and with said terminations.

2. A sealing arrangement as claimed in claim 1, wherein the elastomeric member is in the form of a disc pierced with one or more holes for receiving the terminations therethrough; and wherein the two pressure pads also have through-holes so that the terminations can be inserted through the holes in the pressure pads/elastomeric member sandwich and the whole sandwich assembly constrained within the tubular body in a manner such as to maintain the compressed condition of the elastomer.

3. A sealing arrangement as claimed in claim 1 or 2, wherein the pressure pads and the elastomer have electrically insulating characteristics so as to isolate the terminations from each other and from the surrounding tubular body.

14. A sealing arrangement as claimed in any of claims 1 to 3, wherein the elastomeric body is made of silicone rubber or fluorocarbon rubber.

5. An electronic device of the type having an electronic component contained within an outer tubular housing and which has one or more metal terminations which are to be led out of the outer housing so as to be sealed relative to the outer housing whilst being electrically insulated therefrom, and wherein the or each of the terminations extends through an elastomeric member which is sandwiched in a permanently pressurized condition between a pair of pressure pads, such that the elastomeric member effects sealing both with the inner periphery of the tubular housing and with said termination or terminations.

6. An electronic device as claimed in claim 5, wherein the elastomeric body is in the form of a disc pierced with one or more holes for receiving the terminations therethrough; and wherein the two pressure pads also have through-holes so that the terminations can be inserted through the holes in the pressure pads/elastomeric body sandwich and the whole sandwich assembly constrained within the tubular body in a manner such as to maintain the compressed condition of the elastomer.

7. An electronic device as claimed in claim 6, herein retention of the pressure pads in the tubular body is achieved by peening over the end circumference of the tubular body at its end remote from said electronic component.

8. An electronic device as claimed in claim 6, wherein retention of the pressure pads in the tubular body is achieved by means of a plug received in one end of the tubular body with an interference fit therebetween.

9. An electronic device as claimed in claim 8, wherein said plug has annular frusto-conical protrusions on its peripheral surface which engage with similarly shaped protrusions on the inner wall of the tubular body in order to maintain the required position of the pressure pads.

10. An electronic device as claimed in any of claims 5 to 9 wherein the pressure pads are formed with recesses in the regions where they contact the terminations and the surrounding wall of the tubular body whereby, under pressure, the disc-shaped elastomer is distorted into the spaces provided by these recesses in the pads.

11. An electronic device as claimed in any of claims 5 to 10, wherein said electronic component is an LED.

12. An electronic device as claimed in any of claims 5 to 11, wherein the elastomeric member is made of silicone rubber or fluorocarbon rubber.

13. A sealing arrangement substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

14. An electronic device substantially as hereinbefore described with reference to and as illustrated in Fig. 1, or Fig. 2, or Fig. 3 or Fig. 4 of the accompanying drawings.