ELECTRICAL PRESS-IN CONTACT PIN

Abstract

An electrical contact pin is intended for pressing into a hole which is provided in a circuit carrier board and has a circumferential wall with a metallized surface. The contact pin consists mainly of copper or of a copper alloy and is surrounded by a layer which includes tin at least in a part region which is to be pressed into the hole. The layer, which includes tin, forms the surface of the contact pin and includes substantially only tin and tin oxide, wherein the tin oxide is formed by way of electrolytic oxidation and the concentration thereof is greatest on the surface of the layer.

Claims

1. An electrical contact pin configured to be pressed into a hole of a circuit carrier board, the hole having a circumferential wall with a metallized surface; wherein the contact pin consists primarily of copper or a copper alloy, and is surrounded by a layer containing tin, at least in a region to be pressed into the hole; wherein the layer containing the tin forms a surface of the contact pin, and contains essentially only tin and tin oxide, wherein the tin oxide is formed by electrolytic oxidation, and its concentration is highest at the surface of the layer.

2. The electrical contact pin according to claim 1, wherein the layer containing tin has a thickness of at least 0.2 m.

3. The electrical contact pin according to claim 1, wherein the layer containing tin has a thickness of at least 0.5 m.

4. The electrical contact pin according to claim 1, wherein the layer containing tin has a thickness of 1 m to 3 m.

5. The electrical contact pin according to claim 1, wherein the thickness of the layer containing tin is 1.5 m to 2.5 m.

6. The electrical contact pin according to claim 1, wherein 50 mol % to 80 mol % of tin is present as tin oxide.

7. The electrical contact pin according to claim 1, wherein the layer containing the tin contains only tin oxide at the surface.

8. The electrical contact pin according to claim 1, wherein in the unused state of the contact pin the layer containing the tin contains only tin and oxygen apart from usual or production-related impurities.

9. The electrical contact pin according to claim 1, wherein a diffusion-inhibiting intermediate layer is provided between the layer containing the tin and the core.

10. The electrical contact pin according to claim 9, wherein the diffusion-inhibiting intermediate layer consists of nickel or silver.

11. The electrical contact pin according to claim 9, wherein the diffusion-inhibiting intermediate layer is not thicker than 4 m.

12. The electrical contact pin according to claim 9, wherein the diffusion-inhibiting intermediate layer is 1.5 m to 2.5 m thick.

13. The electrical contact pin according to claim 9, wherein the diffusion-inhibiting intermediate layer is 2 m thick.

14. The electrical contact pin according to claim 1, wherein it consists primarily of a binary copper alloy with 4 to 8% by weight of tin.

15. The electrical contact pin according to claim 1, wherein it consists primarily of a binary copper alloy with 6% by weight of tin.

16. The electrical contact pin according to claim 1, wherein the tin oxide is primarily present as SnO.

17. The electrical contact pin according to claim 16, wherein in the layer containing the tin, at least at the surface and in the vicinity of the surface of the layer containing the tin, SnO predominates over SnO.sub.2 by volume.

18. The electrical contact pin according to claim 16, characterised in that the tin oxide is exclusively present as SnO.

19. An electrical press-in contact pin assembly, comprising: an electrical contact pin; a circuit carrier board having a hole, the hole having a circumferential wall with a metallized surface; wherein the electrical contact pin is configured to be pressed into the hole of the circuit carrier board; wherein the contact pin consists primarily of copper or a copper alloy, and is surrounded by a layer containing tin, at least in a region to be pressed into the hole; wherein the layer containing the tin forms a surface of the contact pin, and contains essentially only tin and tin oxide, wherein the tin oxide is formed by electrolytic oxidation, and its concentration is highest at the surface of the layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In what follows an example of embodiment of the invention is described with the aid of the accompanying figures.

[0029] FIG. 1 is a schematic representation of a detail of a circuit carrier board in a cross-section at right angles to the surface of the circuit carrier board, with a cross-section of a press-fit contact pin, once before it is pressed in, and once after it is pressed into a hole in the circuit carrier board, and

[0030] FIG. 2 shows schematically, and in a much magnified manner, a possible layered structure on a press-fit contact pin in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] FIG. 1 shows a cross-section through a part of a circuit carrier board 1, in which a hole 2 is provided, the circumferential wall of which is metallized and has, for example, a copper layer 3, which covers not only the circumferential wall of the hole 2, but also adjacent regions 4 on the upper face and 5 on the lower face of the circuit carrier board 1. The contact pin 6 is tapered and has a recess 11 near its lower end, which allows an extended region 7 surrounding the recess 11 to be compressed. This happens when the contact pin 6 is pressed into the hole 2; see the lower illustration in FIG. 1. The compression of the extended region 7 of the contact pin 6, and the resulting friction of the contact pin 6 against the metallized wall of the hole 2, causes the electrolytically oxidised tin layer located on the extended region 7 of the contact pin 6 to be abraded. Abrasion of the oxidised tin layer also causes the cold welding of the contact pin 6 to the metallized wall of the hole 2.

[0032] FIG. 2 shows an example of a layered structure of an inventive contact pin 6: On the base body 8 of the contact pin 6, at least in the extended region 7 according to FIG. 1, there is located a diffusion-inhibiting intermediate layer 9 of nickel, and a layer 10 containing tin, which are both, for example, 2 m thick.

[0033] Before the deposition of the diffusion-inhibiting intermediate layer 9 on contact pins 6 made of CuSn6, these were first chemically degreased, and then electrochemically degreased in an alkaline solution. After a washing process, the contact pins 6 were coated with 2 m of nickel in an acidic electrolytic bath based on nickel-methane sulphonate. The nickel-coated contact pins 6 were then activated in a dilute methane sulphonic acid and then coated with 2 m tin in an acidic electrolyte based on tin-II-methane sulphonate.

[0034] The electrolytic oxidation of the tin took place in the alkaline solution, also used for electrochemical degreasing, with a contact pin connected as the anode, at a DC voltage of 5 V to 10 V, for a period of 10 seconds to 30 seconds, wherein oxidation took place for 30 seconds at 5 V, and 10 seconds at 10 V. A subsequent investigation showed that approximately 70 mol % of the tin was then oxidised. The oxidation progressing during the electrolytic treatment was illustrated by a progressive discolouration of the surface of the tin layer, from the original light grey metallic tin to a dark blue colour, which is characteristic for the formation of SnO.

[0035] The progression of the oxidation from the surface into the tin layer is indicated in FIG. 2, in that the density of the hatching in the layer 10 increases from the lower interface with the nickel layer 9 to the surface, wherein the density of the hatching is not true to scale, and has only a symbolic meaning.

[0036] With contact pins coated in this way, press-in and press-out forces were measured and compared to press-in and press-out forces with contact pins coated with nickel and non-oxidised tin. When press-fitted into a hole in a circuit carrier board at a speed of 25 mm/min, a press-fit force of 65 N was measured for a contact pin without an electrolytic oxidation of the tin, and a press-fit force of 66 N was measured when using a press-fit pin with an electrolytically oxidised tin.

[0037] The extraction force when pulling the contact pin out of the hole in the circuit carrier board was measured after the contact pin had been sitting in the circuit carrier board 1 for 24 hours. The extraction force was measured at an extraction speed of 10 mm/min. A force of 78 N was measured when extracting a contact pin without electrolytically oxidised tin, and a force of 80 N was measured when extracting a contact pin with electrolytically oxidised tin. Accordingly, there were no significant differences in the extraction forces between contact pins for which the tin was not oxidised and contact pins for which the tin was electrolytically oxidised.

LIST OF REFERENCE SYMBOLS

[0038] 1 Circuit carrier board [0039] 2 Hole [0040] 3 Copper layer [0041] 4 Region on the upper face [0042] 5 Region on the lower face [0043] 6 Contact pin [0044] 7 Extended region [0045] 8 Base body [0046] 9 Diffusion-inhibiting intermediate layer [0047] 10 Layer containing tin [0048] 11 Recess