ELECTRICAL CONTACT ELEMENT AND A METHOD OF PRODUCING THE SAME

Abstract

The present invention relates to a method of producing an electrical contact element, in which a multilayer structure is formed by applying a diffusion barrier layer to a base material and at least one metallic layer made of a metal to the diffusion barrier layer, at least one layer formed of tin being applied as the metallic layer.

Claims

1. A method of producing an electrical contact element, in which a multilayer structure is formed by applying a diffusion barrier layer to a base material and at least one metallic layer made of metal to the diffusion barrier layer, at least one layer formed of tin being applied as the metallic layer, and by heat-treating the multilayer structure in such a way that at least one element of the layer located under the outer layer of the multilayer structure diffuses into said outer layer and the heat-treated outer layer comprises tin.

2. A method according to claim 1, wherein thermally accelerated diffusion completely throughout the multilayer structure is performed.

3. A method according to claim 1, wherein the outer layer is thoroughly alloyed with the at least one element up to a surface thereof.

4. A method according to claim 1, wherein at least two metallic layers made of different metals are applied to the diffusion barrier layer and the elements of the layers are mixed together by diffusion.

5. A method according to claim 1, wherein the outer layer is formed of tin.

6. A method according to claim 1, wherein at least one layer is selected from the group of: silver, gold, bismuth, iron, indium, zinc, cadmium, tin and/or palladium and is formed under the outer layer.

7. A method according to claim 1, wherein a layer of phosphorus is additionally formed under the outer layer, said layer diffusing into the outer layer.

8. A method according to claim 1, wherein the diffusion barrier layer is formed of nickel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Further details, advantages and features of the present invention will become apparent from the following description of exemplary embodiments together with the drawings, in which:

[0020] FIGS. 1A and 1B are a first schematic sectional representation of one exemplary embodiment of a multilayer structure of an electrical connector element according to the invention before and after heat treatment;

[0021] FIG. 2 shows a comparative example, which shows a multilayer structure not according to the invention of a connector element; and

[0022] FIGS. 3A-3D show further exemplary embodiments of a connector element according to the invention.

[0023] FIG. 4 shows a multilayer structure of a press-fit pin.

DETAILED DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1A shows a multilayer structure 2 of a press-fit pin, in which a diffusion barrier layer 4 formed of nickel has been applied to a base material 6. A 2 m thick outer layer 8 formed of tin is formed on the nickel diffusion barrier layer 4.

[0025] After applying the nickel diffusion barrier layer 4 and the outer layer 8, which is a pure tin layer, the multilayer structure 2 is heat treated at 90 C for 4 hours.

[0026] The duration and temperature of the heat treatment are dependent on the materials used and the desired layer thickness. Since the outer layer 8 is formed of tin, however, the heat treatment temperature should not exceed the melting point of tin, i.e., 232 C.

[0027] Once the heat treatment is complete, the resultant heat-treated multilayer structure 2a comprises a heat-treated recrystallised outer layer 8a (cf. FIG. 1B). This layer 8a consists of a mixture of tin and nickel elements. Due to the heat treatment performed, nickel elements have diffused out of the diffusion barrier layer 4 into the outer layer 8 located thereabove. As is clear from FIG. 1B, the heat treatment performed has brought about complete, thorough mixing of the outer layer 8. The heat-treated outer layer 8a comprises both tin and nickel elements. The heat treatment has the effect, in particular, that the nickel elements diffuse right up to the surface 10 of the outer layer 8, so ensuring that the heat-treated outer layer 8a does not contain any pure tin even close to the surface 10. In this way, a press-fit pin with a contact surface is provided which does not carry any risk of tin whisker formation.

[0028] In contrast to the above exemplary embodiment according to the invention, FIG. 2 shows a comparative example, in which the heat-treated outer layer 8b is a pure tin layer.

[0029] Due to incomplete heat treatment, the outer layer 8b according to the comparative example shown in FIG. 2 is not a thoroughly alloyed layer comprising a mixture of tin and nickel elements. In particular, because of the incomplete heat treatment, no diffusion of the nickel elements up to the surface 10 of the outer layer 8b has been brought about. Although mixing of tin and nickel elements has been achieved (as illustrated by the intermediate layer 12), this comparative example carries a risk of whisker formation, since the outer layer 8b is a pure tin layer.

[0030] FIGS. 3A-3D show a further exemplary embodiment according to the invention, in which a plurality of layers have been applied to the nickel diffusion barrier layer 4.

[0031] FIG. 3A shows a layer 14a formed of silver, which has been formed on the diffusion barrier layer 4. Depending on the desired layer thickness, a plurality of silver layers 14a may also be applied, as shown in FIG. 3B. There, the silver layer 14a has been applied to the diffusion barrier layer 4 alternately with a tin layer 14b. The alternate application of silver and tin layers 14a, 14b forms a sandwich structure, in which the outer layer 8 is a tin layer 14b.

[0032] The resultant multilayer structure 2b is then subjected to a heat treatment method according to the invention, whereby the various layers 14a, 14b are thoroughly alloyed in order to form a heat-treated outer layer 8a consisting of tin and silver elements. A pure tin layer is thus avoided as a constituent of the outer layer 8a (cf. FIG. 3C).

[0033] Depending on the metallurgical characteristics of the layers formed, it is possible, as shown in FIG. 3D, to form an intermediate layer 12a between the heat-treated outer layer 8a and the diffusion barrier layer 4a. Unlike in the comparative example according to FIG. 2, the multilayer structure 2c according to FIG. 3D does not carry any risk of whisker formation, since the outer layer 8a is a thoroughly alloyed outer layer 8a.

[0034] As shown in FIG. 4, a multilayer structure 2d may be formed which is produced from three different elements. FIG. 4 shows a multilayer structure 2d in which a silver layer 16a, a phosphorus layer 16b, and a tin layer 16c are formed alternately on the diffusion barrier layer 4 in such a way that the outer layer 8 is formed of a tin layer 16c.

[0035] This multilayer structure 2d is heat-treated according to the invention in such a way that the plurality of layers 16a, 16b, 16c are thoroughly alloyed, as described above in relation to FIG. 3C.