GB2130253A - Reducing adherence of solder to gripping tools - Google Patents

Abstract

A tool used for handling components during soldering operations has a pair of gripping elements between which the components are held. Each gripping element is of steel and has a layer of chromium carbide on its surface which in turn has a film of chromium oxide on its surface. The oxide film is not wetted by solder, thereby preventing adherence of solder to the tool. The oxide film also prevents material from the tool being dissolved in and contaminating the solder. The oxide film is formed by heating the steel gripping elements in an atmosphere of chromium chloride so that chromium diffuses into the steel to produce the layer of chromium carbide which forms an oxide film on its surface when exposed to air.

Description

SPECIFICATION Reducing the adherence of solder to tools and other articles This invention relates to tools and other articles adapted to reduce the adherence of solder thereto, and to methods of reducing the adherence of solder to articles.

Prior to soldering electronic components into a circuit, it is common practice to tin their leads by dipping in a bath of molten solder.

This ensures that a good soldered joint can be made subsequently, even to leads that may have become contaminated or oxidised on storage. Usually, modified pliers or clamps are employed which have extension pieces mounted at their nose, specially adapted to pick up the components without damage. The extension pieces are usually of mild steel or other metal since this provides a heat sink which reduces the risk that the heat of the solder will damage the component.

These tools have in the past suffered from the disadvantage that the solder eventually wets onto the tool making it unusable. Also, the material from which the tool is made can dissolve in the solder, thereby reducing its purity and possibly having a detrimental effect on the soldered joint.

The adherence of solder to other articles, such as, equipment for the manufacture, handling or transport of solder, can also in some circumstances cause problems.

It is an object of the present invention to provide tools and other articles, and methods of treating such articles, which alleviate to a substantial extent the above-mentioned disadvantages.

According to one aspect of the present invention there is provided a tool or other article for use with molten solder, a part at least of the tool or article being provided with a surface at least of a stable refractory carbide having an oxide film.

According to another aspect of the present invention there is provided a tool or other article for use with molten solder, a part at least of the tool or article being provided with at least a surface film of a chromium oxide.

The film may be formed on the surface of chromium carbide. The tool or other article may include a steel substrate underlying said oxide film.

According to a further aspect of the present invention there is provided a tool or other article for use with molten solder, a part at least of the tool or article being of a steel, a layer of chromium carbide being formed on a surface of the steel, and a film of chromium oxide being formed on the surface of said layer.

It has been found that a surface having such an oxide film is very difficult to wet with solder and can be hard and wear-resistant.

According to yet another aspect of the present invention there is provided a method of forming on a tool or other article for use with molten solder, a surface that is resistant to the adhesion of solder, including the step of providing a part at least of the tool with a surface at least of a stable refractory carbide having an oxide film.

The oxide film may be formed by heating an element of steel, having carbon present in at least a surface layer thereof, in an atmosphere containing a chromium compound so as to produce a diffused layer in the steel of chromium carbide, and allowing a film of chromum oxide to form on the diffused layer in an oxygen-containing atmosphere. The chromium compound may be chromium chloride.

A handling tool and a method of making the tool, 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 side elevation of the tool; Figure 2 is a plan view of the tool of Fig. 1 in the direction of the arrow II; Figure 3 is an enlarged section through a part of the tool showing the carbide layer and oxide film schematically; Figure 4 is a side elevation of a part of an alternative tool; and Figure 5 is a plan view of the tool of Fig. 4 in the direction of the arrow V.

Referring to Figs. 1 and 2, the handling tool comprises a conventional pair of pliers 1 having extension, gripping elements or pieces 2 and 3 joined to the nose 4.

The pliers 1 have two arms 11 and 12 which are jointed at a point 13 close to the nose 4 such that, by opening and closing the rear portions 14 and 15 of the arms the jaws 16 and 17 are correspondingly opened and closed.

The gripping pieces 2 and 3 are each of plate steel 0.79mm in thickness. Each piece is of generally rectangular shape, being 4.76mm wide and 63.5mm long. One piece 2 is formed with a triangular tooth 5 which projects laterally at its forward end, the other piece 3 being formed with a cooperating triangular recess 6 with which the tooth mates when the tool is closed. The contacting edges of the tooth 5 and the recess 6 are formed with cooperating semi-circular notches which together define five small holes 21 to 25 for receiving the leads of a transistor 26 (Fig. 2).

Each gripping piece 2 and 3 is joined at its rear end to a jaw 17 and 16 of a respective arm 12 and 11 by a screw 18 and 19, and two dowels 26 and 27, and 28 and 29. The gripping pieces 2 and 3 may be bent at an angle 8 of about 15 approximately midway along their length, in the manner shown in Fig. 2, so as to facilitate use.

With reference now also to Fig. 3, both gripping pieces 2 and 3 have a coating 50 or chromium carbide. The coating 50 is applied in the following manner. The pieces 2 and 3 are first cut and bent to the required shape.

The steel 51 used for the pieces 2 and 3 either has a bulk carbon content of between about 0.8 to 1 % or is carburized to give a surface layer of between about 0.8 to 1% carbon. A chromium carbide layer 50 is produced by vapour deposition. In this process, the pieces are heated in an atmosphere of chromium chloride so that chromium diffuses into the surface of the pieces to produce a layer of chromium carbide. In air or another oxygen-containing atmosphere, the chromium carbide quickly develops a film 52 of chromium oxide which is highly refractory and inert to the tin and lead present in solder. The oxide film 52 is also self-repairing so that, if the oxide is removed by wear or abrasion, the underlying carbide 50 quickly develops another oxide film. The carbide coating 50 is preferably at least 0.38mm thick.Any solder that splashes onto the coated surface of the tool can easily be knocked off without any sign of interaction with the surface. No contamination of the solder bath is encountered by material dissolved from the handling tool.

Instead of using a layer of chromium carbide formed on a steel substrate, it would be possible to use a member of solid chromium carbide. This, however, would be more difficult to fabricate and is somewhat brittle.

Other materials that could be used include most materials that form a stable refractory oxide film. In this respect, most elements which form a stable refractory carbide and which produce a self-repairing oxide film (such as titanium or tantalum) are particularly useful. It is not essential that the surface be of a carbide since, for example, pure chromium with an oxide layer could be used, although this is not very wear resistant and the surface layer can readily flake off.

An alternative handling tool is shown in Figs. 4 and this is for use with resistors and capacitors. Again, this tool is formed by modifying conventional pliers 1, by the addition of extension, gripping pieces 32 and 33.

The extension pieces 32 and 33 are of the same material as the extension pieces 2 and 3 shown in Figs. 1 and 2, and are provided with a chromium carbide surface layer in the manner described earlier. Each extension piece 32 and 33 is formed from a single strip of steel 6.4mm wide and 250mm long. The strip is bent back on itself, both ends of the strip being secured to one of the jaws of the pliers by screws 34. The forward end 35 of the extension pieces 32 and 33 is formed into a lozenge-shape loop 36, the electrical component 40 being held between the loops 36 of the two extension pieces 32 and 33.

It will be appreciated that the present invention can find application with other equipment and articles used for the handling of molten solder. In this respect, it may be found advantageous in other electronic component assembly equipment, solder manufacturing equipment and so on.

Claims (16)

1. A tool or other article for use with molten solder, wherein a part at least of the tool or article is provided with a surface at least of a stable refractory carbide having an oxide film.

2. A tool or other article for use with molten solder, wherein a part at least of the tool or article is provided with at least a surface film of a chromium oxide.

3. A tool or other article according to Claim 2, wherein said film is formed on the surface of a stable refractory carbide.

4. A tool or other article according to any one of the preceding claims, wherein said film is formed on the surface of chromium carbide.

5. A tool or other article according to any one of the preceding claims including a steel substrate underlying said oxide film.

6. A tool or other article for use with molten solder, wherein a part at least of the tool or article is of a steel, wherein a layer of chromium carbide is formed on a surface of the steel, and wherein a film of chromium oxide is formed on the surface of said layer.

7. A tool according to any one of the preceding claims, including a handle and gripping elements attached thereto that can be opened and closed to retain a component for soldering, wherein said part at least of the tool is provided by said gripping elements.

8. A tool for retaining a component during a soldering operation including a handle and gripping elements attached thereto that can be opened and closed to retain said component, wherein said gripping elements are of a steel that is formed with a layer of chromium carbide on its surface, and wherein a film of chromium oxide is formed on the surface of said layer.

9. A tool substantially as hereinbefore described with reference to the accompanying drawings.

10. A method of forming on a tool or other article for use with molten solder, a surface that is resistant to the adhesion of solder, including the step of providing a part at least of the tool with a surface at least of a stable refractory carbide having an oxide film.

11. A method of providing on a tool or other article for use with molten solder, a surface that is resistant to the adhesion of solder, including the step of providing a part at least of the tool with a surface film of chromium oxide.

12. A method according to Claim 10 or 11, wherein said oxide film is formed by heating an element of steel, having carbon present in at least a surface layer thereof, in an atmosphere containing a chromium compound so as to produce a diffused layer in the steel of chromium carbide, and allowing a film of chromium oxide to form on the diffused layer in an oxygen-containing atmosphere.

13. A method according to Claim 12, wherein said chromium compound is chromium chloride.

14. A method substantially as hereinbefore described with reference to the accompanying drawings.

15. A tool or other article for use with molten solder having a surface that is resistant to the adhesion of solder, formed by a method according to any one of Claims 10 to 14.

16. Any novel feature or combination of features as hereinbefore described.