GB2040110A - Electric shorting devices - Google Patents

Abstract

An electric shorting device 11 for leadless mounting on a printed circuit board includes a cylindrical carbon ceramic or porcelain body 12 which is plated with an electrically conducting metal layer 13. Electrically conductive end caps 14 and 15 are fitted to each end of the plated body 12 and a layer 16 of non-conducting material is applied between the caps 14 and 15. The use of ceramic, carbon or porcelain for the body 12 results in a shorting device 11 having a heat capacity close to that of other leadless components on the printed circuit board so that the time required to melt solder applied to end caps 14 and 15 of device 11 is comparable with the time required to melt the solder applied the electrodes of other components. <IMAGE>

Description

SPECIFICATION Electric shorting devices This invention relates to electric shorting devices suitable for use in printed circuits.

According to the present invention there is provided an electric shorting device comprising: a cylindrical body; a layer of an electrically conducting metal coating said body; and two conductive end caps received by and carried upon respective end portions of said body.

The invention will now be described by way of example with reference to the accompanying drawing, in which: Figure 1 is a perspective view of a conventional electric shorting device on a printed circuit board; Figure 2 is a cross-sectional view of the device of Figure 1; and Figure 3 is a cross-sectional view of an embodiment of electric shorting device according to the invention.

Before describing the embodiment, a conventional electric shorting device will be described with reference to Figures 1 and 2.

A conventional electric shorting device 1, or a so-called "jumper part", comprises larger cylindrical portions 2 and 3, and a smaller cylindrical portion 4, all made of conductive material. On a printed circuit board 5, conductors 7 and 8 are formed on opposite sides of a conductor 6, and are separated from each other as shown in Figure 1. The conductors 7 and 8 are electrically connected to each other by the shorting device 1 which bridges the conductor 6.

A rod of brass may be machined by a lathe to form the larger cylindrical portions 2 and 3 and the smaller cylindrical portion 4 with predetermined dimensions. The entire surface of the shorting device 1 is then plated with nickel, or 95% tin and 5% solder.

However, an undesirable whisker-like projection or burr 9 is often formed on the end surface of one of the larger cylindrical portions 2 and 3 during the machining.

Generally, an automatic mounting apparatus is used for mounting various electronic parts onto a printed board, and a part feeder is included in such apparatus. When shorting devices 1 move through the part feeder, they are often caught by internal projections of the part feeder because of the projections or burrs 9. This of course results in disturbance to the smooth flow of parts. Accordingly, removal of the projections or burrs 9 is required, causing the manufacturing cost to increase.

In the mounting process, the shorting devices 1 and other electronic parts are provisionally attached to predetermined conductors on a printed circuit board with solder cream. They are then heated in a gas furnace or by infra-red rays to melt the solder cream which, after cooling, firmly attaches them to the conductors. However, the time required to melt the solder cream applied to the larger cylindrical portions 2 and 3 of the shorting device 1 is longer than the time required to melt the solder cream applied to the electrode portions of the electronic parts. This is because the shorting device 1 is entirely made of metal having a high thermal conductivity, and therefore heat is rapidly transmitted away from the metal surface to the internal portion of the shorting device 1.

The embodiment will now be described with reference to Figure 3. An electronic shorting device 11 includes a cylindrical body 12 preferably made of a ceramic such as porcelain. The circumferential surface of the body 12 has tapered ends 12a and 1 2b formed, for example, by a barrel polishing method.

Due to the tapered ends 12a and 12b, caps 14 and 15 can easily be fitted to the respective ends of the body 12.

Ceramics such as porcelain are lighter than brass, which is a typical material for the conventional shorting device 1. Accordingly, the shorting device 11 when provisionally attached to a printed board does not fall off as easily as does the conventional shorting device 1.

The body 12 is first plated with metal such as silver or copper by a non-electrolytic plating method, to a depth of about 2 microns. Then, the metal layer so obtained is plated with a metal such as silver or copper by an electrolytic plating method, to a depth of about 50 to 60 microns. Thus, the metal layer 13 as shown in Figure 3 is formed on the body 12. In order to prevent oxidation, the metal layer 13 may be further plated with nickel.

The caps 14 and 15 are made of conductive metal such as brass or iron with a thickness of about 200 microns. They are also plated, using a tin material containing 5 to 10% of solder. The caps 14 and 15 are fitted to the end portions of the body 12 by a driving-fit or impacting method so that the contact resistance between the metal layer 13 and the caps 14 and 15 is satisfactorily low.

Thermo-setting epoxy resin or an ultravioletsetting resin may be used to form an insulating film 16 which is coated onto the metal layer 13 to a depth which is generally smaller than the thickness of the caps 14 and 15, that is, less than about 200 microns.

The insulating layer 16 has enlarged portions adjacent to the caps 14 and 15. It is preferably that the additional depth t of the enlarged portions of the insulating film 16 at the edges of the caps 14 and 15 is smaller than about 50 microns. The dimensions ~,1 and 12 as shown in Figure 3 are as follows: ~ = 2.2 mm or 2.5 mm Ii = 6 mm or8 mm 12= 1.5 mum The internal resistance of the shorting device 11, namely the resistance between the caps 14 and 15, can be as low as 4 to 5 milliohms. Generally, the internal resistance required for a jumper part is lower than about 10 milliohms.

The thermal conductivity of the body 12 made of ceramics such as porcelain is low. Accordingly, the time required to melt the solder cream applied to the caps 14 and 15 of the shorting device 11 is less than that of the conventional shorting device 1, and it is comparable to the time required to melt the soldered cream applied to the electrode portions of the electronic parts.

The cylindrical body of leadless carbon resistor may be used as the cylindrical body 12, in which case a manufacturing apparatus for carbon resistors can be used for the shorting devices 11, so they can be mass-produced economically.

Claims (10)

1. An electric shorting device comprising: a cylindrical body; a layer of an electrically conducting metal coating said body; and two conductive end caps received by and carried upon respective end portions of said body.

2. A device according to claim 1 further comprising a layer of insulating material overlying said electrically conducting layer between said caps.

3. A device according to claim 1 wherein said metal is silver.

4. A device according to claim 1 wherein said metal is copper.

5. A device according to claim 1 wherein said electrically conducting layer comprises an inner layer of non-electrolytically applied metal, and an outer layer of electrolytically applied metal.

6. A device according to claim 1 wherein said body has tapered end portions.

7. A device according to any one of the preceding claims wherein said body is made of ceramic.

8. A device according to claim 7 wherein said ceramic is porcelain.

9. A device according to any one of claims 1 to 6 wherein said body is made of carbon.

10. An electric shorting device substantially as hereinbefore described with reference to Figure 3 of the accompanying drawing.