WO1997050149A1

WO1997050149A1 - Making an electrical joint

Info

Publication number: WO1997050149A1
Application number: PCT/GB1997/001608
Authority: WO
Inventors: William Thomas Large; Stylianos Panaghe
Original assignee: Delta Theta Limited
Priority date: 1996-06-21
Filing date: 1997-06-13
Publication date: 1997-12-31
Also published as: AU3100697A; GB9613046D0

Abstract

There is disclosed a method for making an electrical joint between terminals comprising the steps of contacting the terminals together and passing an electric current through the terminals so contacted so as to melt at least one of the terminals and thus weld it to the other.

Description

MAKING AN ELECTRICAL JOINT

This invention relates to making electrical joints, in particular, but not exclusively, to joints conventionally made by soldering or by using electrically conductive epoxy adhesives such for example as in joining a wire (or a terminal tag on a wire) to a terminal pad printed or otherwise deposited on a steel or ceramic substrate. Such joints are required particularly in domestic appliances such as toasters, kettles, irons and cookers.

It is a problem with such joints that the heat generated during ordinary operation of the appliance but more particularly when such appliances overheat, as is not uncommon, can damage the joints, which have limited temperature tolerance. A soldered joint, for example, will fail if the temperature exceeds the melting point of the solder, about 200 °C. Spring loaded contacts may be useful up to 300°C but not higher and are likely to degrade with prolonged or repeated exposure to temperatures less than this.

Welding would be a solution to the problem, since welded joints would survive up to the melting temperature of the wiring, but conventional welding methods - electric are or torch welding - are normally unsuitable for use in the context.

The present invention provides a method for making electrical joints which is quick and simple to carry out, which makes joints of good integrity and which will survive elevated temperatures better than, in most cases substantially better than, conventional methods. The invention comprises a method for making an electrical joint between terminals comprising the steps of contacting the terminals together and passing an electric current through the terminals so contacted so as to melt at least one of the terminals and thus weld it to the other.

The terminals may be pressed together during the step of passing the electrical current. While the terminals may be pressed together between electrodes through which the melting current is supplied, analogously to spot-welding, this may not always be possible, and the current will usually more easily be supplied through at least one of the terminals being joined. It will usually be possible to arrange that the joint is not effected over the whole area or cross-section of the terminals so that current density in the wire and/or pad, for example, will not be sufficient to raise its temperature to melting point except in the restricted region of the joint.

Pressure at the joint can also sufficiently depress the melting point to cause only local melting while leaving the rest of the terminal unaffected.

It is desirable, of course, not to heat any part of the arrangement that has plastic insulation to a temperature at which that is adversely affected.

Methods for making an electrical joint according to the invention will now be described with reference to the accompanying drawing, of which :

Figure 1 is a diagrammatic view of a first method, and Figure 2 is a diagrammatic view of a second method.

The drawings illustrate methods for making an electrical joint between terminals 11, 12 comprising the steps of contacting the terminals 11, 12 together and passing an electric current I through the terminals so contacted so as to melt at least one of the terminals and thus weld it to the other.

The terminals 11, 12 are pressed together during the step of passing the electric current. In the arrangement of Figure 1, the terminals are pressed together by an insulated pressing bit, shown diagrammatically as Arrow A which presses terminal 11 - a wire end - on to terminal 12 - a printed copper terminal on a ceramic pad 13 which serves as an anvil. Current I is passed through terminals 11, 12 from any convenient location - the remote end, for example, of a wire of which terminal 11 is one end, and a remote terminal connected to the printed strip of which terminal 12 is one end.

Figure 2 shows a similar arrangement except that the current I is supplied through pressing bit 14.

The energy to raise the temperature of the areas of contact between the electrodes 11, 12 can be measured and calculated as a function of the voltage V across the terminals and the current I as well as the duration T of application, and a timer 15 can be set to cut off the current after time T, as shown in Figure 1. PC17GB97/01608

In Figure 2, an ammeter 16 is shown which measures the current I and acts current when there is a change in the measured current which is indicative ving been achieved.

Claims

£LΔJMS

1. A method for making an electrical joint between terminals comprising the steps of contacting the terminals together and passing an electric current through the terminals so contacted so as to melt at least one of the terminals and thus weld it to the other.

2. A method according to claim 1, in which the terminals are pressed together during the step of passing the electric current.

3. A method according to claim 2, in which the terminals are pressed together between electrodes through which the melting current is applied.

4. A method according to any one of claims 1 to 3, in which the energy supplied to the terminals as computed for example from the voltage, current and duration of the application of the current is just sufficient to effect the melting and hence welding.

5. A method according to any one of claims 1 to 4, in which the current is monitored to detect a change due to melting have occurred and the current cut off when this change is detected.