PRODUCTION OF SURFACE-MODIFIED CU RIBBONS FOR LASER BONDING

Abstract

The invention relates to a method for producing a wire, having at least the following steps: (i) providing a wire precursor; (ii) pressing depressions on the wire precursor and optionally reshaping the wire precursor in the process, and (iii) annealing the wire precursor provided with depressions in order to form the wire; wherein the wire has a content of at least 95 wt. % of copper based on the total weight of the wire. The invention additionally relates to a wire which can be obtained according to the aforementioned method and to the use of a roller in order to produce the wire and/or in order to set the roughness at at least one location of the wire.

Claims

1. A method for producing a wire, comprising at least the following steps: (i) providing a wire precursor; (ii) pressing depressions on the wire precursor; and (iii) annealing the wire precursor provided with depressions in order to obtain the wire; wherein the wire has a content of at least 95 wt. % of copper, the content being based on the total weight of the wire.

2. The method according to claim 1, wherein the pressing is selected from the group consisting of punch marking, notching, embossing, stamping, channeling and grooving.

3. The method according to claim 1, wherein the pressing is carried out by rollers.

4. The method according to claim 3, wherein the rolling is carried out by at least one roller, wherein the roller has a cylindrical surface comprising a relief, wherein the relief is formed by height differences of the cylindrical surface.

5. The method according to claim 4, wherein the height difference is in a range from 3 to 9 μm.

6. The method according to claim 1, wherein the depressions form a pattern.

7. The method according to claim 1, wherein the wire has a plurality of locations, wherein the depressions are only introduced at a first location.

8. The method according to claim 1, wherein the wire has a roughness R.sub.z in a range from 3 to 9 μm at least one location.

9. The method according to claim 7, wherein at least one further location of the wire is smooth, wherein the at least one further location is located on the location of the wire facing away from the first point.

10. The method according to claim 1, wherein the wire is a bonding wire, preferably a ribbon.

11. The method according to claim 1, wherein an element selected from the group consisting of the wire and the wire precursor has a cross-sectional area Q.sub.A in a range from 25,000 to 900,000 μm.sup.2, wherein the cross-sectional area Q.sub.A is arranged perpendicularly to a longitudinal direction L of the element.

12. The method according to claim 1, wherein a cross-sectional plane QE is laid through an element selected from the group consisting of the wire precursor and the wire, wherein the cross-sectional plane Q.sub.E is arranged perpendicularly to a longitudinal direction L of the element, wherein the cross-sectional plane Q.sub.E forms a cross-sectional area Q.sub.A with the element, wherein the cross-sectional area Q.sub.A comprises two perpendicularly intersecting lines L1 and L2, wherein a shortest possible section A.sub.L1 of the line L1 is defined by an intersection with the edge of Q.sub.A, and wherein a longest possible section A.sub.L2 of the line L2 is defined by an intersection with the edge of Q.sub.A, wherein the quotient of A.sub.L2 and A.sub.L1 is a number of 2 or more.

13. A wire obtainable by a method according to claim 1.

14. A use of a roller comprising a relief for producing a wire, wherein the relief has a height difference in a range from 3 to 9 μm, wherein depressions are introduced by the roller at least one location of the wire.

15. The use of a roller comprising a relief for setting the roughness R.sub.z at least one location of a wire in a range from 3 to 9 μm, wherein the relief has a height difference.

16. A method for producing a device comprising at least one electrically conductive connection, wherein the method comprises the following steps: (I) providing a substrate having at least a first contact surface, and a wire, wherein the wire can optionally be obtained by a method according to claim 1; (II) positioning the wire in a mechanical connection with the first contact surface; (III) heating a first location of the wire by means of electromagnetic radiation in a wavelength range from 700 to 1,100 nm, to obtain an electrically conductive connection between the first contact surface of the substrate and the wire, wherein the first location of the wire has a roughness R.sub.z in a range from 3 to 9 μm, for example from 4 to 8 μm, or 5 to 7 μm, or 4 to 9 μm, or 5 to 9 μm, wherein a further location of the wire facing away from the first location of the wire, which faces the contact surface, has a roughness R.sub.z in a range from 0.1 to 1 μm, wherein the roughness R.sub.z at least the first location of the wire was produced by pressing selected from the group consisting of punch marking, notching, embossing, stamping, channeling and grooving, or a combination of two or more thereof.

17. The method according to claim 16, wherein the first location of the wire or the first side of the wire is arranged on the side of the wire facing away from the first contact surface of the substrate.

18. The method according to claim 16, wherein the roughness R.sub.z at least the first location of the wire was brought about by rolling, wherein, for rolling, preferably a roller comprising a relief was used to produce a wire, by means of which roller depressions were introduced on at least one location of the wire, wherein the relief has a height difference in a range from 3 to 9 μm.

Description

FIGURES

[0130] In the following, the present invention is illustrated further by way of example with reference to figures and examples. Neither the figures nor the examples represent a limitation of the claimed subject matter.

[0131] FIG. 1 shows a schematic view of a wire or of a wire precursor.

[0132] FIG. 2 shows a view of a cross-sectional area Q.sub.A of the object shown in FIG. 1.

[0133] FIG. 3 schematically shows a method for introducing depressions into a wire.

[0134] FIG. 4 shows a ribbon a) with a relief, b) with brushing.

[0135] FIG. 5 schematically shows a device with a wire and a contact surface.

DESCRIPTION OF THE FIGURES

[0136] FIG. 1 shows a schematic view of a wire 2 or a wire precursor 1 characterized by its length L and a cross-sectional plane Q.sub.E.

[0137] FIG. 2 shows a view of a cross-sectional area Q.sub.A, as part of the cross-sectional plane Q.sub.E shown in FIG. 1. Two lines L1, L2 perpendicular to each other are laid through the cross-sectional area Q.sub.A. They intersect the cross-sectional area Q.sub.A in the edges of the wire 2 or of the wire precursor 1. Therefore, the sections A.sub.L1 and A.sub.L2 of the lines L1 and L2 are formed.

[0138] FIG. 3 schematically shows a method for introducing depressions 3 into a wire 2 by means of a roller with a relief (upper roller, without reference signs). The lower roller is optional and can be replaced by another counter surface.

[0139] FIG. 4 shows the surface topography a) of a ribbon 2 with an introduced pattern 6 made of depressions 3; b) of a brushed ribbon.

[0140] FIG. 5 schematically shows a device 10 comprising a wire 2 which connects a first contact surface 12 to a second contact surface 13.

[0141] Test Methods

[0142] a. Determining the Relief Height and Roughness

[0143] The determination of the relief height D and the roughness R.sub.z of the wire was based on the standards DIN EN ISO 4287 (2010-07) (Definition and parameters) and DIN EN ISO 4288 (1998-04) (Rules and procedures), wherein the relief height of the roller and the roughness of the wire were determined transversely to the rolling direction. In deviation from the standard DIN EN ISO 4288, as a result of the geometric conditions, the ribbon was measured over a short sampling length and over the whole measuring length. A sufficiently long sampling length was defined as at least one third of the ribbon or of the effectively used roller width. A Mahr Perthometer PCV with a 2 μm diamond tip was used. The determination was carried out at at least two different locations of the wire or the roller. The measured data were evaluated based on DIN EN ISO 4287 using the MahrSurface XCR20 V1.20-4 program.

[0144] b. Determining the Cross-Sectional Area of a Wire or Ribbon

[0145] To determine the cross-sectional area, a metallographic section was prepared and measured with the aid of an optical microscope.

EXAMPLES

[0146] In the following, the invention is illustrated further by examples. The invention is not limited to the examples and feature combinations or parameters shown therein.

[0147] 1. Producing Copper Ribbons

[0148] Copper round wires having a diameter of 0.78 mm and a purity of 99.98 wt % Cu were used as the starting material. The wires were guided by a reshaping system having two rollers made of hard metal in the arrangement outlined in FIG. 3. The roller no. 1 (in the figure at the bottom) was a smooth cylinder with a diameter of 96 mm. The roller no. 2 (in the figure at the top) also had a basic cylindrical shape with a diameter of 96 mm. In the case of the reshaped wires (1)-(3), the surface of the roller no. 2 had a relief with a relief height D (D.sub.max). In the case of the reshaped wires (A) and (B), the surface of the roller no. 2 was smooth and had no relief structure whatsoever. The wires were guided between the rollers no. 1 and no. 2, rotating in opposite directions but in the direction of transport of the wires. The rollers no. 1 and no. 2 had a roller gap S between them. This was set and determined as the shortest distance between the surface of the roller no. 1 and the surface of the basic cylindrical shape of the roller no. 2, i.e., at a location without a relief. The output speed of the wires in the transport direction was identical to the rotational speed v of the rollers on the contact surface with the wire. The rolling oil used was a rapidly volatilizing rolling oil B-Clean 62S. After the rolling step, the reshaped wires (1)-(3) and (A) and (B) were annealed in a 2.5 m long continuous furnace at a throughput rate of 10 m/min and an annealing temperature T.sub.G of 650° C. in a hydrogen atmosphere. After annealing, the reshaped wires were cooled to ambient temperature. After the annealing process, the reshaped comparison wires (A) and (B) were brushed according to the characteristics in Table 2. The characteristics of the reshaped wires (1)-(3) are given in Table 1.

TABLE-US-00001 TABLE 1 Ex. no. (1) (2) (3) Relief height D (μm) 4.88 8.63 20.85 D.sub.max roller (μm) 5.99 11.41 22.38 Roller gap size S 0.2 Rotational speed v 45 m/min Dimensions of the ribbon/cross-sectional 0.20 × 2.05 area of the ribbon after reshaping R.sub.max (μm) 3.88 9.15 19.19 Roughness R.sub.z (μm) 3.32 6.824 18.612

TABLE-US-00002 TABLE 2 Ex. no. (A) (B) Dimensions of the ribbon/cross-sectional 0.20 × 2.05 area of the ribbon after reshaping Roughness R.sub.max before brushing (μm) 0.87 Roughness R.sub.z before brushing (μm) 0.679 Brush material High-strength steel roller brushes Brush wire diameter [μm] 1 × 200 + 1 × 200 1 × 100 Rotational speed of brushes [U/min] 900 Ribbon speed [m/min] 3 1 Roughness R.sub.max after brushing (μm) 4.55 10.96 Roughness R.sub.z after brushing (μm) 3.16 6.24

[0149] 2. Assessing the Quality of the Reshaped Wires

TABLE-US-00003 Ex. no. (1) (2) (3) (A) (B) Residue on the + + + − − − reshaped wire surface Spatters occurring + + − − − − − during the laser bonding process

[0150] For one thing, scanning electron microscope images were used to assess the quality of the reshaped wires visually with regard to unwanted residues on the surface: [0151] +: no residues, −: little residue, ——: much residue

[0152] In the next step, the behavior of the reshaped wires during laser bonding was investigated with regard to the potential occurrence of spatter behavior. For this purpose, the reshaped wires were bonded in identically constructed electronic components under the same settings of the laser bonder. Spatters that occurred were counted using an optical microscope: [0153] +: no spatter, −: little spatter, ——: much spatter.

[0154] It was observed that the brushed, reshaped wires (A) and (B) showed residues on the surface. In this case, more residues were identified on the surface in the case of the larger depressions introduced. These residues led to spatter behavior of the brushed, reshaped wires (A) and (B) during the laser bonding process. In contrast, no residues could be found on the surfaces of the reshaped wires (1)-(3).

[0155] The reshaped wires (1) and (2) having a roughness R.sub.z of less than 9 μm did not demonstrate any spatter behavior in the laser bonding process. In contrast, the reshaped (3) having an increased roughness R.sub.z of 18.6 μm demonstrated a clear spatter behavior in the laser bonding process.

LIST OF REFERENCE SIGNS

[0156] 1 Wire precursor [0157] 2 Wire [0158] 3 Depression [0159] 4 Roller [0160] 5 Surface of the roller [0161] 6 Relief [0162] 7 First side [0163] 8 Further side [0164] 10 Device [0165] 11 Substrate [0166] 12 First contact surface [0167] D Height difference [0168] Q.sub.E Cross-sectional plane [0169] Q.sub.A Cross-sectional area [0170] L Length [0171] L1, L2 Line [0172] A.sub.L1, A.sub.L2 Section