US-12620510-B2 - Method of producing a surface finish on an electrically conductive substrate and electric conductor with the surface finish thereon

US12620510B2US 12620510 B2US12620510 B2US 12620510B2US-12620510-B2

Abstract

A method for producing a surface finish on an electrically conductive substrate includes transferring an ink having a plurality of electrically conductive particles onto an area of a predetermined form and/or size on a surface of the electrically conductive substrate by gravure and/or flexo printing. The ink is heated to a temperature that is higher than a melting point of the electrically conductive particles to create a melt. The melt solidifies into the surface finish on the electrically conductive substrate.

Inventors

Shallu Soneja
Yiliang Wu
Gokce Gulsoy
Helge Schmidt
Soenke Sachs

Assignees

TE CONNECTIVITY GERMANY GMBH
TE CONNECTIVITY SOLUTIONS GMBH

Dates

Publication Date: 20260505
Application Date: 20230623
Priority Date: 20220624

Claims (19)

1 . An electric conductor, comprising: an electrically conductive substrate having a surface with an area of predetermined size and/or form on which a surface finish is applied, the surface finish is produced by: transferring an ink having a plurality of electrically conductive particles onto the area by gravure and/or flexo printing; and heating the ink to a temperature that is higher than a melting point of the electrically conductive particles to create a melt, which solidifies into the surface finish on the electrically conductive substrate, a layered structure is formed in the area that has an intermetallic phase and a layer of solid electrically conductive particles.
2 . The electric conductor of claim 1 , wherein the layer of solid electrically conductive particles forms a top layer of the surface finish.
3 . The electric conductor of claim 1 , wherein a plurality of edges of the surface finish have a lateral resolution of less than 1 mm.
4 . The electric conductor of claim 1 , wherein the surface finish has a predetermined variation of thickness within the area.
5 . The electric conductor of claim 1 , wherein the surface finish has a thickness from about 0.75 to about 5 micrometers.
6 . The electric conductor of claim 1 , wherein the surface finish has an organic material from about 0.01 to about 0.5 wt % organic material.
7 . The electric conductor of claim 1 , wherein the surface finish has a particulate structure on the surface.
8 . An electric conductor, comprising: an electrically conductive substrate having a surface with an area of predetermined size and/or form on which a surface finish is applied, a plurality of edges of the surface finish have a lateral resolution of less than 1 mm, the surface finish is produced by: transferring an ink having a plurality of electrically conductive particles onto the area by gravure and/or flexo printing; and heating the ink to a temperature that is higher than a melting point of the electrically conductive particles to create a melt, which solidifies into the surface finish on the electrically conductive substrate.
9 . An electric conductor, comprising: an electrically conductive substrate having a surface with an area of predetermined size and/or form on which a surface finish is applied, the surface finish has an organic material from about 0.01 to about 0.5 wt % organic material, the surface finish is produced by: transferring an ink having a plurality of electrically conductive particles onto the area by gravure and/or flexo printing; and heating the ink to a temperature that is higher than a melting point of the electrically conductive particles to create a melt, which solidifies into the surface finish on the electrically conductive substrate.
10 . An electric conductor, comprising: an electrically conductive substrate having a surface with an area of predetermined size and/or form on which a surface finish is applied, the surface finish has a particulate structure on the surface, the surface finish is produced by: transferring an ink having a plurality of electrically conductive particles onto the area by gravure and/or flexo printing; and heating the ink to a temperature that is higher than a melting point of the electrically conductive particles to create a melt, which solidifies into the surface finish on the electrically conductive substrate.
11 . A method for producing a surface finish on an electrically conductive substrate, comprising: transferring an ink having a plurality of electrically conductive particles onto an area of a predetermined form and/or size on a surface of the electrically conductive substrate by gravure and/or flexo printing, the ink is a first ink having a first set of electrically conductive particles and is transferred to a first area of predetermined form and/or size by gravure and/or flexo printing, and a second ink having a second set of electrically conductive particles is transferred to a second area of predetermined form and/or size, a material of the first set of electrically conductive particles is different than a material of the second set of electrically conductive particles; and heating the first ink and the second ink to a temperature that is higher than a melting point of the first set and the second set of electrically conductive particles to create a melt, which solidifies into the surface finish on the electrically conductive substrate.
12 . The method of claim 11 , wherein the first ink and the second ink are heated by induction heating the electrically conductive substrate.
13 . The method of claim 11 , wherein the first set of electrically conductive particles comprise tin.
14 . The method of claim 11 , wherein the first ink and the second ink are melted in subsequent steps.
15 . The method of claim 14 , wherein the first ink is melted via induction heating.
16 . The method of claim 15 , wherein the second ink is melted via electron beam melting.
17 . The method of claim 11 , wherein the first set of electrically conductive particles has an average particle size of about 2 μm to about 5 μm.
18 . The method of claim 11 , wherein the first ink has a dynamic viscosity below 10 Pa s, measured at 10 s −1 at 25° C.
19 . The method of claim 11 , wherein the first set of electrically conductive particles has an oxygen content of less than 1 wt %.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application claims the benefit of the filing date under 35 U.S.C. § 119(a)-(d) of European Patent Application No. 22181010.4, filed on Jun. 24, 2022. FIELD OF THE INVENTION The present invention relates to a method of producing a surface finish on an electrically conductive substrate. Furthermore, the invention relates to an electric conductor comprising an electrically conductive substrate with a surface finish thereon. BACKGROUND Electric conductors are used in a variety of applications to form electric connections with mating conductors. The electric conductors, such as electric contacts, comprise an electrically conductive substrate, such as copper or a copper alloy, for transferring the electricity. To facilitate the connection movement of electric contacts and prevent surface damage due to oxidation and other causes, electric contacts are provided with a surface finish. Traditionally, surface finishes are applied onto the electrically conductive substrate using electroplating, electroless plating, physical vapor deposition, or hot dipping. These processes are expensive and/or a surface finish based on tin tends to form whiskers. SUMMARY A method for producing a surface finish on an electrically conductive substrate includes transferring an ink having a plurality of electrically conductive particles onto an area of a predetermined form and/or size on a surface of the electrically conductive substrate by gravure and/or flexo printing. The ink is heated to a temperature that is higher than a melting point of the electrically conductive particles to create a melt. The melt solidifies into the surface finish on the electrically conductive substrate. BRIEF DESCRIPTION OF THE DRAWINGS Exemplary embodiments of the invention are described by way of the following drawings. In the drawings: FIG. 1 shows a schematic flow chart for producing a surface finish on an electrically conductive substrate according to an exemplary embodiment of the invention; FIG. 2 shows a top view of an electric conductor having a surface finish, according to an exemplary embodiment of the invention; FIG. 3 a cross-section scanning electron microscope (SEM) image of the surface finish showing an intermetallic layer and free Sn layer; and FIG. 4 a top view SEM image showing the particulate structure. DETAILED DESCRIPTION OF THE EMBODIMENT(S) In the following, exemplary embodiments of a method of producing a surface finish and electric conductor are explained in greater detail with reference to the accompanying drawings. In the figures, the same reference numerals are used for elements that correspond to one another in terms of their function and/or structure. According to the description of the various aspects and embodiments, elements shown in the drawings can be omitted if the technical effects of these elements are not required for a particular application, and vice versa, i.e. elements that are not shown or described with reference to the figures, but are otherwise described herein, can be added if the technical effect of those particular elements is advantageous in a specific application. FIG. 1 is a schematic flow chart of a method for producing a surface finish on an electrically conductive substrate. According to the exemplary embodiment, an electrically conductive substrate 2, which may comprise or consist of copper or a copper alloy, has a surface 4. An ink 6 with electrically conductive particles 8, in particular tin or tin alloy particles, is transferred onto an area 10 of predetermined form and/or size on the surface 4 via gravure printing in the exemplary embodiment shown. Alternatively, the ink 6 with the electrically conductive particles 8 could be transferred via flexo printing instead of gravure printing, or the ink 6 could be transferred using a combination of gravure printing and flexo printing. In an embodiment, the electrically conductive particles 8 in the ink 6 may comprise or consist of tin. The term “tin” pertains to pure tin and/or tin alloys, such as SAC, which is a tin silver copper alloy. The tin alloy may for example have a tin content of about 96.5 wt %, a silver content of about 3.5 wt % and a copper content of about 0.5 wt %. A tin surface finish protects the substrate from corrosion and is highly reliable for establishing electric interconnections between the conductors and mating conductors at a low cost. Using the above method for tin finishes is particularly advantageous as cost savings of up to 65% compared to the cost of a hot dipped Sn finish can be achieved. The gravure printing process uses a cylinder 12 having engraved cells 14 on its surface 16. These cells 14 are flooded with ink 6, wherein any excess can be removed with a doctor blade 18. These engravings can have patterns which may be square, rectangle, oval, circle, stripes etc. which helps with material savings and can be custom designed to the product. The ink 6 from the cells 14 is then transf