Sintering paste and use thereof for connecting components

Abstract

The invention relates to a sintering paste consisting of: (A) 30 to 40 wt. % of silver flakes with an average particle size ranging from 1 to 20 m, (B) 8 to 20 wt. % of silver particles with an average particle size ranging from 20 to 100 nm, (C) 30 to 45 wt. % of silver(I) oxide particles, (D) 12 to 20 wt. % of at least one organic solvent, (E) 0 to 1 wt. % of at least one polymer binder, and (F) 0 to 0.5 wt. % of at least one additive differing from constituents (A) to (E).

Claims

1. A sintering paste consisting of: (A) 32 to 37 wt. % of silver flakes with an average particle size ranging from 1 to 20 m; (B) 10 to 16 wt. % of silver particles with an average particle size ranging from 20 to 100 nm; (C) 32 to 40 wt. % of silver(I) oxide particles; (D) 12 to 20 wt. % of at least one organic solvent; (E) 0 to 1 wt. % of at least one polymer binder; and (F) 0 to 0.5 wt. % of at least one additive differing from constituents (A) to (E).

2. The sintering paste according claim 1, wherein the silver particles have an aspect ratio ranging from 1:1 to 5:1.

3. The sintering paste according to claim 1, wherein the silver(I) oxide particles have an average particle size ranging from 0.4 to 4 m.

4. The sintering paste according to claim 1, wherein the at least one organic solvent is a combination of at least one terpineol with at least one dibasic ester.

5. The sintering paste according to claim 1, wherein the at least one polymer binder is selected from cellulose derivatives.

6. The sintering paste according to claim 1, wherein at least a portion of the silver particles is adhered to at least a portion of the silver flakes.

7. A method for producing the sintering paste according to claim 1, the method comprising mixing constituents (A) to (D) with one another, wherein constituents (A) and (B) are first premixed with one another.

8. A method for connecting components, the method comprising: (1) providing a sandwich arrangement, the sandwich arrangement comprising at least two components and a sintering paste according to claim 1 located between the components; (2) optionally drying the sintering paste; and (3) sintering the sandwich arrangement.

9. The method according to claim 8, wherein at least one of the at least two components consists of aluminum or an aluminum alloy.

10. The method according to claim 8, wherein the sintering paste is applied by means of dispensing technology.

11. The method according to claim 8, wherein sintering is carried out under pressure or in an unpressurized manner.

12. The method according to claim 8, wherein the components are component parts for electronics.

13. A method for connecting components, the method comprising: (1) providing a sandwich arrangement, the sandwich arrangement comprising at least two components and the sintering paste, the sintering paste produced by a method according to claim 7 and located between the components; (2) optionally drying the sintering paste; and (3) sintering the sandwich arrangement.

14. The method of claim 13, the method comprising drying the sintering paste.

15. The method of claim 8, the method comprising drying the sintering paste.

16. The method according to claim 8, wherein at least one of the at least two components comprises an aluminum contact surface or an aluminum-based contact surface by which the sandwich arrangement is made.

17. The method according to claim 7, wherein constituents (A) to (E) are mixed with one another.

18. The method according to claim 7, wherein constituents (A) to (F) are mixed with one another.

19. The sintering paste of claim 1, wherein at least one of the silver particles and the silver(I) oxide particles comprise an organic coating.

Description

EXAMPLES

(1) 1. Production of Sintering Pastes:

(2) The compositions of the sintering pastes 1, 2 and 3 according to the invention and of the comparative pastes C1, C2 and C3 in percent by weight are listed in Table 1.

(3) In the case of sintering paste 1, the silver flakes and the silver particles were premixed in a tumbling mixer for 120 min and then added to the further paste constituents listed in Table 1. By contrast, the silver flakes and the silver particles were not premixed in sintering pastes 2 and 3 as well as in comparative pastes C1, C2 and C3, but were instead added directly to the further paste constituents.

(4) TABLE-US-00001 TABLE 1 Composition of sintering pastes 1, 2 and 3 according to the invention and of comparative pastes C1, C2 and C3 1 2 3 C1 C2 C3 Silver flakes* 36.4 32.9 30.5 52.0 58.8 15.6 Silver particles** 15.6 14.1 9.0 25.2 32.4 Silver(I) oxide*** 32.0 37.0 44.5 32.0 32.0 Ethyl cellulose 0.3 0.3 0.3 0.3 0.3 0.3 Terpineol 7.85 7.85 7.85 7.85 7.85 9.85 Dimethyl succinate 7.85 7.85 7.85 7.85 7.85 9.85 *Silver flakes: D50: 3 m, coated with 0.7 wt. % of a 1:1 mixture of stearic acid and lauric acid **silver particles: D50: 50 nm, coated with 1.5 wt. % of oleic acid ***silver(I) oxide: D50: 1.7 m, uncoated

(5) 2. Evaluation of the Sintering Pastes:

(6) The sintering pastes 1, 2 and 3 according to the invention and the comparative pastes C1, C2 and C3 were investigated with regard to their drying behavior, their recovery capacity after shear loading and their sintering capacity on aluminum and copper surfaces.

(7) 2.1. Evaluating the Drying Behavior:

(8) To evaluate the drying behavior, the pastes were each first applied in the shape of a square (5 cm5 cm) and with a wet film thickness of 300 m to the surface of an aluminum sheet by means of stencil printing. Subsequently, the surfaces of the wet non-dried pastes were each completely covered with a 1 mm thick glass platelet, such that only the outer edges of the pastes were exposed. These test structures were then placed on a heating plate and the paste layers covered with the glass platelets were dried at 130 C. for 15 min. The formation of any drying channels or defects was investigated with the aid of an optical microscope and assessed as indicated in Table 2.

(9) 2.2. Evaluation of the Recovery Rate after Shear Loading:

(10) The recovery rate after shear loading was determined for the various sintering pastes by means of rotational viscometry using the plate-and-cone measuring principle at a cone diameter of 25 mm and a cone angle of 2 with a measuring gap of 0.05 mm at a variable shear rate. For this purpose, a measurement run was selected at which an abrupt change to a high shear rate of 100 s.sup.1 lasting for 30 seconds took place starting with a low shear rate of 30 s.sup.1 lasting for 30 seconds. This measurement run was repeated a total of twelve times. The recovery rate was determined as a percentage change in the final viscosity compared with the initial viscosity [(quotient of final viscosity and initial viscosity)100%]. The initial viscosity is defined as the last measuring point at a low shear rate in the first measurement run and the final viscosity as the last measuring point at a low shear rate in the twelfth measurement run.

(11) 2.3. Determination of Shear Strength:

(12) To determine the sintering capacity on aluminum and copper, the shear strengths of each sintering connection material were determined on aluminum and copper. For this purpose, the sintering pastes according to the invention and the comparative pastes were applied by means of stencil printing to an aluminum sheet of 5 mm thickness and to the 300 m thick copper surface of a DCB substrate with a wet film thickness of 50 m. Subsequently, the applied sintering pastes were pre-dried at 140 C. for 10 min and then contacted over the full area with a silicon chip having a silver contact surface (4 mm4 mm). The subsequent pressure sintering was carried out under a nitrogen atmosphere (<100 ppm oxygen) in a hot press at 230 C. and 12 MPa for 5 minutes. For the purpose of determining the shear strength, the components were sheared off at 20 C. with a shear chisel at a speed of 0.3 mm/s. The force was recorded by means of a load cell (device: DAGE 2000 from DAGE, Germany).

(13) TABLE-US-00002 TABLE 2 Evaluation of sintering pastes 1, 2 and 3 according to the invention and comparative pastes C1, C2 and C3 with regard to drying behavior, recovery rate directly after shear loading and shear strength on aluminum and copper surfaces 1 2 3 C1 C2 C3 Drying behavior Very good, no Very good, no Good, individual, Poor, defects Poor, many Poor, many drying channels drying channels small drying and large drying drying defects and visible visible channels visible channels visible channels drying channels visible visible Initial viscosity 25.5 18.5 34.0 22.0 29.5 56.0 (Pa .Math. s) Final viscosity 20.5 15.5 27.0 17.0 16.0 10.0 (Pa .Math. s) Recovery rate 80.4 83.8 79.4 77.3 54.2 17.9 (%) Shear values on ./. 40 52 6 0 0 aluminum surface [N/mm.sup.2] Shear values on 44 45 55 24 14 9 copper surface [N/mm.sup.2]