Metal paste and use thereof for joining components

Abstract

A metal paste, comprising (A) 65 to 85 wt % of metal particles and (B) 10 to 35 wt % of organic solvent, wherein the metal particles (A) consist 70 to 100 wt % of organically coated copper flakes having a specific surface area in the range of 1.9 to 3.7 m.sup.2/g, a total oxygen content in the range of 2 to 4 wt % and a weight ratio of total carbon to total oxygen in the range of 0.25 to 0.9.

Claims

1. A metal paste, comprising (A) 65 to 85 wt % of metal particles and (B) 10 to 35 wt % of organic solvent, wherein the metal particles (A) consist of 70 to 100 wt % of organically coated copper flakes having a specific surface area in the range of 1.9 to 3.7 m.sup.2/g, a total oxygen content in the range of 2 to 4 wt %, and a weight ratio of total carbon to total oxygen in the range of 0.25 to 0.9.

2. The metal paste according to claim 1, wherein the organically coated copper flakes are thin plates measuring 40 to 200 nm having an aspect ratio in the range of 6:1 to 375:1.

3. The metal paste according to claim 1, wherein the organically coated copper flakes have a mean particle size (d50) in the range of 1 to 15 μm.

4. The metal paste according to claim 1, wherein the organic coating forms a bonded and non-volatile layer on the surface of the copper flake at 20° C. and atmospheric pressure.

5. The metal paste according to claim 1, wherein the organic coating comprises at least one type of organic coating compounds.

6. The metal paste according to claim 1, wherein the organic coating is 2 to 5 wt % of the organically coated copper flakes.

7. The metal paste according to claim 1, wherein the organically coated copper flakes have a coating level of 0.004 to 0.006 g/m.sup.2.

8. The metal paste according to claim 1, wherein the organically coated copper flakes are made of flakes made of copper alloys having up to 30 wt % of at least one alloy metal.

9. The metal paste according to claim 8, wherein the at least one alloy metal is selected from the group consisting of silver, gold, nickel, palladium, platinum, zinc, and aluminum.

10. The metal paste according to claim 1, further comprising up to 15 wt % of at least one additive (C) selected from the group consisting of metal precursors, sintering aids, dispersing agents, surfactants, defoaming agents, binding agents, polymers, and viscosity-controlling agents.

11. A method for joining components, the method comprising: preparing a sandwich arrangement that includes at least one component 1, one component 2 and one metal paste according to claim 1, the metal paste located between contact surfaces of component 1 and component 2; and bonding the contact surfaces of component 1 and component 2 by sintering the metal paste.

12. The method according to claim 11, wherein at least one of the contact surfaces that are to be bonded by sintering is a contact surface made of copper or of a metallized copper.

13. The method according to claim 11, wherein sinter bonding occurs while applying pressure, or pressureless.

14. The method according to claim 11, wherein the one component 1 and the one component 2 are parts that are used in electronics.

15. The method according to claim 11, wherein the sinter bonding occurs within a temperature range of 250 to 350° C.

16. The method according to claim 1, wherein the total oxygen content is in the range of 2.5 to 4 wt %.

17. The metal paste according to claim 1, wherein the organically coated copper flakes are made of pure copper flakes.

18. The metal paste according to claim 1, wherein the organically coated copper flakes are made of pure copper flakes and flakes made of copper alloys having up to 30 wt % of at least one alloy metal.

19. The metal paste according to claim 1, wherein the metal paste comprises 70 to 80 wt % of the metal particles and 15 to 30 wt % of the organic solvent.

20. The metal paste according to claim 1, wherein the metal paste comprises 72 to 78 wt % of the metal particles and 17 to 28 wt % of the organic solvent.

Description

EXAMPLES

(1) 1. Preparation of the Copper Pastes:

(2) Each of the pastes P1-P4 (comparative pastes) and P5-P9 (each according to the invention) with comparable processing viscosity were prepared initially by mixing organically coated copper flakes with α-terpineol.

(3) TABLE-US-00001 Comparison pastes P1 P2 P3 P4 Organically coated 73 75 67 83 copper flakes [wt %] α-terpineol [wt %] 27 25 33 17 Organic coating Stearic Stearic Stearic Stearic acid acid acid acid Specific surface of 1.88 3.31 1.24 1.01 the organically coated copper flakes [m.sup.2/g] Total oxygen content 2.8626 4.9282 4.04 0.45 of organically coated copper flakes [wt %] Weight ratio of total 0.15 0.22 0.13 1.52 carbon to total oxygen in organically coated copper flakes Pastes according to the invention P5 P6 P7 P8 P9 Organically coated 75 75 75 75 75 copper flakes [wt %] α-terpineol [wt %] 25 25 25 25 25 Organic coating Stearic Stearic Stearic Stearic Stearic acid acid acid acid acid Specific surface of 3.31 2.04 2.31 3.70 1.95 the organically coated copper flakes [m.sup.2/g] Total oxygen content 3.07 2.72 3.25 3.82 2.83 of organically coated copper flakes [wt %] Weight ratio of total 0.37 0.44 0.33 0.39 0.36 carbon to total oxygen in organically coated copper flakes

(4) 2. Application and Sinter Bonding of Copper Pastes:

(5) Using stencil printing, each copper paste was applied to a DCB substrate with a wet film thickness of 100 μm and an area of 4 mm-4 mm full area. Drying occurred subsequently inside the convection oven at 80° C. for a duration of 30 minutes, thus removing α-terpineol. Silicon chips were placed onto the dried pastes by their contact surfaces of 4 mm.Math.4 mm, at a temperature of 25° C. The silicon chips were heated at 15 MPa and 300° C. for 3 minutes in a nitrogen atmosphere for sinter bonding the components with the DCB.

(6) After sintering, the adhesion was determined based on the shear strength. In doing so, the silicon chips therein were sheared using a shear chisel at a speed of 0.3 mm/s at room temperature. The force was recorded using a load cell (instrument Nordson DAGE 4000Plus by the company Nordson DAGE, Germany).

(7) The following table shows the obtained measured results:

(8) TABLE-US-00002 Shear test [N/mm.sup.2] Paste *Target shear strength: ≥20 N/mm.sup.2 P1 5.50 P2 8.76 P3 0.59 P4 13.13 P5 46.10 P6 49.90 P7 25.89 P8 51.01 P9 41.20