GB2248565A

GB2248565A - Manufacturing tined electrical contact

Info

Publication number: GB2248565A
Application number: GB9119708A
Authority: GB
Inventors: Brian Shepherd
Original assignee: Smiths Group PLC
Current assignee: Smiths Group PLC
Priority date: 1990-10-10
Filing date: 1991-09-16
Publication date: 1992-04-15
Anticipated expiration: 2011-09-16
Also published as: GB9021982D0; GB9119708D0; GB2248565B

Abstract

An electrical contact for insertion into a hole in a printed circuit board (3) is made by machining a circular blank (20) of phosphor bronze or beryllium copper to give it a triangular or other polygonal section (11) along a part of its length. A bore (21) is then drilled axially from one end of the blank, the radius of which is such that it breaks through the wall of the polygonal section (11) between its corners so that it is divided into e.g. three resilient tines. Alternatively, the blank is firstly bored and then machined externally to a polygonal shape again to break through the wall of the blank to form the tines. <IMAGE>

Description

ELECTRICAL CONTACTS AND THEIR MANUFACTURE This invention relates to electrical contacts and their manufacture.

The invention is more particularly concerned with the manufacture of compliant contacts for insertion into a hole such as in a printed circuit board.

Compliant contacts provide a mechanical and electrical connection with a hole in a board or the like, by means of the resilience in the contact itself. The contacts generally have metal tines that are deflected inwardly when inserted into the hole so that a resilient outward force is exerted by the tines to grip the hole.

If the hole is plated with a metal, an electrical connection can also be provided. The contacts can be soldered in the holes for a more permanent mounting.

Compliant contacts can take many different forms and be made in many different ways. Most commonly, the contacts are made from a flat metal sheet which is stamped and rolled or folded to produce resilient tines.

Alternatively, as described in GB 2161035, a barrel shape blank can be machined from a suitable metal and radial slots milled into the blank so that they meet in the centre to divide the barrel into separate, parallel resilient tines.

Contacts made by stamping and bending from sheet metal can be of low cost but cannot be made easily to the high standards of accuracy required in many applications.

Contacts made by milling slots into a blank, by contrast, can be made very accurately to close tolerance but are relatively expensive.

It is an object of the present invention to provide an improved contact and a method of manufacturing such a contact.

According to one aspect of the present invention there is provided a method of manufacture of an electrical contact including the steps of providing an elongate metal blank a part at least of the length of which is of substantially polygonal section, drilling a bore axially into the blank the radius of which bore is less than the radius of the polygonal part of the blank at its corners and greater than the radius of the polygonal part of the blank intermediate its corners such that the bore cuts through the wall of the blank intermediate the corners and divides each corner of the blank into a resilient tine.

The method may include the preliminary step of providing an elongate metal blank of circular section and machining it to produce the said part of polygonal section. The part of polygonal section is preferably spaced from opposite ends of the blank so that the bore only cuts through the wall over an intermediate region of the contact and so that the tines are joined together at both ends. One end of the contact may have a diameter that exceeds the lateral dimensions of the part of polygonal section. An end of the contact may have a diameter less than the lateral dimensions of the part of polygonal section. The bore may be drilled only a part of the way along the length of the blank. The shape of the polygonal section may be such that the bore divides the part into three tines. The polygonal section may be an equilateral triangle shape in section.The contact may have a socket at one end adapted to receive a pin therein.

The blank may be of phosphor bronze or beryllium copper.

According to another aspect of the present invention there is provided a method of manufacture of an electrical contact including the steps of forming an axial bore into a metal blank from one end and machining away the outer surface of the blank in a region overlying the bore so as to form a substantially polygonal section that breaks through into the bore and divides the region into at least two resilient tines.

According to a further aspect of the present invention there is provided an electrical contact made by a method according to the one or other aspect of the present invention.

Electrical contacts and their method of manufacture, in accordance with the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a contact; Figure 2 is a transverse sectional view of the contact of Figure 1 in a board; Figure 3 is a sectional side elevation view of the contact along the line III - III of Figure 2; Figure 4 is a perspective view of the contact at a preliminary stage of manufacture; Figure 5 is a transverse sectional view along the line V-V of Figure 4; Figure 6 is a perspective view of the contact at the next stage of manufacture; Figure 7 is a transverse sectional view along the line VII - VII of Figure 6; Figure 8 is a sectional elevation view of the blank at a later stage of manufacture;; Figure 9 is an enlarged transverse section across the contact along the line IX IX illustrating its construction; and Figures 10 are transverse sections across to 13 alternative contacts.

With reference first to Figures 1 to 3, the compliant contact 1 is inserted into a plated hole 2 in a printed circuit board 3. The contact is of a resilient metal such as phosphor bronze or beryllium copper and is plated with gold. At its lower end, the contact 1 has a solid stem 10 of circular section which projects below the lower surface of the board. The stem 10 joins with an intermediate, resilient section 11 which is hollow and has three parallel tines 12, 13 and 14 which extend parallel to the axis of the contact and are equally spaced around its circumference. The natural external lateral dimensions or diameter of the resilient section 11 is shown by the broken lines in Figure 3 and exceeds both the diameter of the stem 10 and that of the hole 2.When inserted in the hole 2, the tines 12 to 14 are bent resiliently inwardly to the position shown by the solid lines in Figure 3, in which the external diameter of the resilient section 11 matches that of the hole 2. The tines 12 to 14 grip the hole 2 and provide a good mechanical and electrical connection with the board 3.

The upper end of the contact 1 is provided by an annular shank 15 which is of circular section and is uninterrupted around its circumference so that it joins together the upper end of the tines 12 to 14, with which it is integrally formed, and prevents them being displaced inwardly. The external diameter of the shank 15 exceeds the diameter of the hole 2 so that downward displacement of the contact 1 in the hole is limited. The shank 15 may receive a conventional socket assembly (not shown) such as of the kind sold by Hypertac Limited, in which several spring wires extend obliquely of the socket axis around its circumference and make a sliding contact with a male pin inserted within the socket.

The contact 1 is manufactured in the manner shown in Figures 4 to 9. Firstly, a length of circular barstock 20 of beryllium copper or phosphor bronze is placed in the chuck 100 of a polygon turning machine 101 and this is turned to machine the left-hand stem end 10, adjacent the chuck, to a smaller diameter than the remainder of the length of barstock 20, as shown in Figures 4 and 5. If the hole 2 in the circuit board 3 is lmm in diameter, the stem 10 will have a diameter somewhat less than lmm.

The intermediate, resilient section 11 is then machined to an equilateral triangular section by polygon turning in which a cutting tool 102 oscillates radially inwardly and outwardly three times for each revolution of the barstock 20, as shown in Figures 6 and 7, cutting tangentially into the barstock. The setting of the machine 101 is such that the greatest radius Rl of the triangular shape, that is, from the centre to the corner or apex, is slightly greater than the radius of the hole 2 in the circuit board. The machine is preferably also set to leave rounded apexes to the triangular section.

The next step (not shown) is to turn the right hand end of the barstock 20 to the desired external diameter of the shank 15 and to cut this to the desired length.

Following this, as shown in Figures 8 and 9, an axial bore 21 is drilled with a tool 103 into the right-hand end of the machined barstock. The bore 21 extends along the barstock, through the shank portion 15 and the intermediate portion 11, terminating just to the right of the stem 10. The radius r2 of the bore 21 is chosen so that it is less than the greatest radius R1 of the triangle but greater than the smallest radius R2, that is, from the centre of the bore 21 to the midpoint along a side. In this way, the bore 21 breaks through the wall of the intermediate section 11 leaving three tines 12 to 14 which are separated from one another along their length but joined and supported at both ends. The rounded apexes of the triangle give the tines 12 to 14 a smooth, rounded surface for engagement with the hole 2.If stiff tines are required, the radius r2 of the bore 21 is close to R2 so that the tines are wide and the space between them is small. Less stiff tines are made by increasing the radius r2 of the bore 21 so that the tines become thinner and the space between them becomes greater.

The final step in the manufacture is to cut off the stem from that portion of the barstock in the chuck 100.

Instead of using polygon turning, it would be possible remove regions of sector shape from the blank to produce the same triangular shape by other machining techniques, such as by milling. The term polygons is used here to indicate any regular shape of two or more sides which need not be straight sides. For example, the tools on the machine may be such as to produce the trefoil or star shapes as shown in Figures 10 and 11. This would still produce a contact with three tines. Alternatively, the polygon could be four sided, as shown in Figure 12 to produce four tines, or two sided, as shown in Figure 13 to produce two tines. It will be appreciated that the tines will become thinner and more delicate the greater their number and that this will reduce the resilient force with which the contact is retained in the hole 2.It has been found that the three tines produced with a three-sided polygon can be sufficiently robust to exert the desired resilient force on the hole.

Instead of machining the barstock to a polygon shape and then drilling the axial bore it would be possile to drill the bore first into barstock of circular section and then to machine away the external surface of the barstock into a polygon shape and to a depth at which the bore is broken into.

The stem 10 of the contact could be used merely as an introducer to the hole 2 (and could be cut off after insertion), or it could be shaped as a pin to mate with a cooperating socket (not shown) below the board 3.

Alternatively, the stem 10 could have flats for wire wrapping. The shank 15 need not act as a socket but could, for example, receive some other form of mating contact or coupling, or be used as a post to which a wire could be soldered. The bore 21 could extend along the entire length of the contact, opening at the lower end of the stem to form a female socket. In the arrangements described above, the tines are restrained at both ends, by the stem 10 and shank 15 respectively, and the method of manufacture is particular useful in enabling a unitary body of this kind to be produced. It is not, however, essential that the tines be retained at both ends, since the tines could, for example, extend to the end of the contact and be separated from one another along their length. It would also be possible to use a separate member to retain the free ends of the tines.

The contact of the present invention can be made accurately at relatively low cost, the tines providing a very stable mechanical and/or electrical connection in the hole in the board.

Claims

1. A method of manufacture of an electrical contact including the steps of providing an elongate metal blank a part at least of the length of which is of substantially polgonal section, drilling a bore axially into the blank the radius of which bore is less than the radius of the polygonal part of the blank at its corners and greater than the radius of the polygonal part of the blank intermediate its corners such that the bore cuts through the wall of the blank intermediate the corners and divides each corner of the blank into a resilient tine.

2. A method according to Claim 1, including the prelimary step of providing an elongate metal blank of circular section and machining it to produce the said part of polygonal section.

3. A method according to Claim 1 or 2, wherein the part of polygonal section is spaced from opposite ends of the blank so that the bore only cuts through the wall over an intermediate region of the contact and so that the tines are joined together at both ends.

4. A method according to Claim 3, wherein one end of the contact has a diameter that exceeds the lateral dimensions of the part of polygonal section.

5. A method according to Claim 3 or 4, wherein an end of the contact has a diameter less than the lateral dimensions of a part of polygonal section.

6. A method according to any one of the preceding claims, wherein the bore is drilled only a part of the way along the length of the blank.

7. A method according to any one of the preceding claims, wherein the shape of the polygonal section is such that the bore divides the part into three tines.

8. A method according to Claim 7, wherein the polygonal section is an equilateral triangle shape in section.

9. A method according to any one of the preceding claims, wherein the contact has a socket at one end adapted to receive a pin therein.

10. A method according to any one of the preceding claims, wherein the blank is of phosphor bronze.

11. A method according to any one of Claims 1 to 9, wherein the blank is of beryllium copper.

12. A method substantially as hereinbefore described with reference to Figures 1 to 9 of the accompanying drawings.

13. A method substantially as hereinbefore described with reference to Figures 1 to 9 as modified by any one of the Figures 10 to 13 of the accompanying drawings.

14. An electrical contact made by a method according to any one of the preceding claims.

15. A method of manufacture of an electrical contact including the steps of forming an axial bore into a metal blank from one end and machining away the outer surface of the blank in a region overlying the bore so as to form a substantially polygonal section that breaks through into the bore and divides the section into at least two resilient tines.

16. A method according to Claim 15, wherein the polygonal section is of triangular section.

17. A method according to Claim 15 or 16, wherein the polygonal section is spaced from opposite ends of the blank.

18. An electrical contact made by a method according to any one of Claims 15 to 17.

19. An electrical contact substantially as hereinbefore described with reference to Figures 1 to 9 of the accompanying drawings.

20. An electrical contact substantially as hereinbefore described with reference to Figures 1 to 9 as modified by Figures 10 to 13 of the accompanying drawings.

21. Any novel feature or combination of feature as hereinbefore described.