GB2204740A

GB2204740A - Housings for electrical components

Info

Publication number: GB2204740A
Application number: GB08710399A
Authority: GB
Inventors: Brian Beer; Peter Nelson Stenning
Original assignee: Otehall Ltd
Current assignee: Otehall Ltd
Priority date: 1987-05-01
Filing date: 1987-05-01
Publication date: 1988-11-16
Anticipated expiration: 2007-05-01
Also published as: GB2204740B; GB8710399D0

Abstract

An electrical component for mounting on printed circuit boards or other analogous supports is enclosed within a housing of a resilient mouldable plastics material and has one or more connecting pins or tags 4 extending through a wall 1 of the housing via a through-hole provided in that wall. Each of the through-holes is provided with a constricted region, such as the web 3 tapering to an edge 3a, which tightly embraces around the connecting pin or tag 4 passing therethrough. Such an arrangement prevents the ingress of corrosive or inhibiting vapour or fluid into the component arising from the flux used during soldering of the component on to the printed circuit board or analogous support. <IMAGE>

Description

ELECTRICAL COMPONENTS The present invention relates to electrical components and more particularly to electrical components which are enclosed within a housing of a mouldable plastics material and have one or more connecting pins or tags extending through a wall of the housing via a through-hole provided in that wall. Such components are commonly employed for mounting on printed circuit boards or other analogous supports comprising a series of conductor paths.

A component may be mounted so that its connecting pins or tags extend through apertures in the board or analogous support, whereby the pins or tags serve not only as connections between the component and the adjacent conductor paths but also serve to locate the component in position. Alternatively the connecting pins or tags may be in the form of pads by which a component rests on the printed circuit board or analogous support and is oriented so that its various connections make contact with the appropriate conductor paths. In either case, the connecting pins or tags are bonded to the adjacent conductor paths by some kinds of soldering technique. One technique employs a solder paste applied to the support which is re-flowed after the component or components are placed in position in order to effect the bonding of the component connections to the desired conductor paths.Another technique is to employ wave soldering to bond components in position on a support.

In either case a problem occurs in that the flux or other compound employed in connection with the soldering operation or an adhesive employed to locate a component, gives rise to a corrosive or inhibiting vapour or liquid which can enter into the component through the small gap existing between each connecting pin or tag and the adjacent wall of the housing where the pin or tag passes through the wall. This corrosive or inhibiting vapour or liquid seeping into the housing or drawn therein by capillary action can cause damage to and/or deterioration of the component contained within the housing, or a high resistance or opencircuit condition, and thereby a resulting defect in or failure of that component.More specifically the problem caused by a soldering flux drawn on to a component by vapour condensation or capillary action can result in either tracking or high resistance problems or contamination or malfunctioning of the component.

It is an object of the present invention to provide a means of alleviating these problems.

The present invention provides an electrical component enclosed within a housing of a mouldable plastics material and having one or more through-holes extending through a wall of the housing through each of which passes a connecting pin or tag for connecting the component to an external circuit wherein each of said through-holes, as formed in the moulded housing, is provided with a constricted region which tightly embraces a connecting pin or tag passing therethrough.

In this way the ingress of corrosive or inhibiting vapour or fluid into the component by seepage or capillary action around a connecting pin or tag is substantially avoided.

Preferably the constricted region is provided adjacent the external surface of the wall of the housing. The constricted region may be formed by an inwardly directed peripheral web defining the boundary of the through-hole adjacent the external surface of the wall of the housing.

The invention may be applied to any shape of through-hole intended to receive a complementary shape of connecting pin or tag and more specifically the through-holes may be of square, rectangular or circular cross section.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figs. la, lb and lc are respectively a plan view and two sectional views of a portion of one embodiment of component housing according to the invention, Figs. 2 and 2b illustrate the insertion of a connecting pin into a through-hole, Fig. 3 is a scrap perspective showing a connecting pin projecting from the wall of the housing; and Fig. 4 is a sectional view of a component mounted on a printed circuit board.

Referring to Figs. la, lb and lc, there is shown at 1 a part of a wall of a housing for an electrical component, which housing is formed of a mouldable plastics material such as The wall is provided with a rectangular through-hole 2 which locates and forms a passage for a connecting pin of corresponding cross-section. The region of the through-hole 2 adjacent the outer wall of the housing is constricted by forming that edge of the hole with an inwardly directed peripheral web 3 tapering to an edge 3a.

The plastics material forming the housing is slightly resilient andFigs. 2a and 2b illustrate the action of passing a connecting pin 4 into the through-hole 2. As can be seen from Fig. 2b, when the pin 4 has passed through the hole 2, the web 3 is deflected so that its edge 3a tightly embraces the sides of the pin 4. In this way the ingress of corrosive or inhibiting vapour or fluid into the housing by seepage or capillary action around the connecting pin is virtually eliminated.

Although only a portion of the housing and one connecting pin have been shown to illustrate the principle of the invention, it will be understood that in practice a component will generally have several connecting pins.

A complete component contained within a housing 1 and mounted on a printed circuit board 5 is shown in Fig. 4 with the connecting pins 4 connected by soldering to associated conductor paths 6 forming part of the printed circuit. The component within the housing 1 may be of many kinds, for example a resistor, a capacitor, semiconductor, or switch.

It will be apparent that various modifications may be made without departing from the scope of this invention. For example the constriction of the through-holes may be formed by other configurations than the web 3 and the through-holes and associated connecting pins may be of other than rectangular cross-section.

The technique of the present invention may advantageously be employed in the manufacture of many forms of surface mounted components.

Claims

1. An electrical component enclosed within a housing of a resilient mouldable plastics material and having one or more through-holes extending through - wall of the housing through each of which passes a connecting pin or tag for connecting the component 0 an external circuit wherein each of said throughholes, as formed in the moulded housing, is provide with a constricted region which tightly embraces around a connecting pin or tag passing therethrough.

2. An electrical component as claimed in claim 1, wherein the constricted region is provided adjacent the external surface of the wall of the housing.

3. An electrical component as claimed in claim 1 cr 2, wherein the constricted region is formed by an inwardly directed peripheral web defining the boundary of the through-hole adjacent the external surface c- the all of the housing.

4. An electrical component as claimed in any preceding claim wherein the through-holes are of square or rectangular cross section and receive a complementary shape of connecting pin or tag.

5. An electrical component as claimed in any of claims 1 to 3, wherein the through-holes are of circular cross section and receive a complementary shape of connecting pin or tag.

6. An electrical component as claimed in any preceding claim, wherein the component is a surface mounted component provided with connecting tags in e form of pads.

7. An electrical component substantially as hereinbefore described with reference to the accompanying drawings.