Silver sintering preparation and the use thereof for the connecting of electronic components

Abstract

A silver sintering preparation in the form of a silver sintering paste comprising 70 to 95 wt.-% of coated silver particles (A) and 5 to 30 wt.-% of organic solvent (B) or in the form of a silver sintering preform comprising 74.5 to 100 wt.-% of coated silver particles (A) and 0 to 0.5 wt.-% of organic solvent (B), wherein the coating of the coated silver particles (A) comprises silver acetylacetonate (silver 2,4-pentanedionate) and/or at least one silver salt of the formula C.sub.nH.sub.2n+1COOAg with n being an integer in the range of 7 to 10, and wherein the at least one silver salt is thermally decomposable at >160? C.

Claims

1. A silver sintering preparation, the preparation in the form of a silver sintering paste comprising 70 to 95 wt.-% of coated silver particles (A) and 5 to 30 wt.-% of organic solvent (B), or a silver sintering preform comprising 74.5 to 100 wt.-% of coated silver particles (A) and 0 to 0.5 wt.-% of organic solvent (B), wherein the coating of the coated silver particles (A) comprises silver acetylacetonate (silver 2,4-pentanedionate) and, wherein the coated silver particles (A) have a mean particle diameter (d.sub.50) ranging from 0.2 to 20 ?m.

2. The silver sintering preparation of claim 1, wherein the silver sintering preparation is a silver sintering paste comprising 75 to 85 wt.-% of the coated silver particles (A) and 8 to 25 wt.-% of organic solvent (B).

3. The sintering preparation of claim 1, wherein the silver sintering preparation is a silver sintering preform comprising 96 to 100 wt.-% of the coated silver particles (A) and 0 to 0.5 wt.-% of organic solvent (B).

4. The silver sintering preparation of claim 1, wherein the fraction of the silver acetylacetonate silver 2,4-pentanedionate), relative to the entire coating, is at least 60 wt.-%.

5. The silver sintering preparation of claim 1, wherein the fraction of the silver acetylacetonate (silver 2,4-pentanedionate) is ?20 wt.-%, relative to the weight of the coated silver particles (A).

6. The silver sintering preparation of claim 1, wherein the coated silver particles (A) have a mean particle diameter (d.sub.50) ranging from 0.5 to 20 ?m.

7. The silver sintering preparation of claim 1, wherein the coated silver particles (A) have a mean particle diameter (d.sub.50) ranging from 0.2 to 10 ?m.

8. The silver sintering preparation of claim 1, wherein the silver sintering preparation further comprises up to 2.5 wt.-% of at least one cellulose derivative and/or up to 5 wt.-% of at least one fatty compound, wherein the at least one cellulose derivative is selected from the group consisting of methylcellulose, ethylcellulose, ethylmethylcellulose, carboxycellulose, hydroxypropylcellulose, hydroxyethylcellulose, hydroxymethylcellulose and combinations thereof, the at least one fatty compound is selected from the group consisting of fatty acids, fatty acid esters, fatty acid salts, fatty alcohols, fatty amines, fatty amides and combinations thereof, and when the silver sintering preparation comprises at least one cellulose derivative and at least one fatty compound, the combination of the at least one cellulose derivative and the at least one fatty compound is no more than 4 wt.-% of the silver sintering preparation.

9. The silver sintering preparation of claim 1, wherein the silver sintering preparation is free of polymers other than cellulose derivatives, dispersion agents, surfactants defoaming agents, rheological agents and sintering agents.

10. The silver sintering preparation of claim 1, wherein the coating of the coated silver particles (A) further comprises at least one silver salt of the formula C.sub.nH.sub.2n+1COOAg with n being an integer in the range of 7 to 10 wherein the at least one silver salt is thermally decomposable at >160? C.

11. The silver sintering preparation of claim 10, wherein n is an integer ranging from 7 to 9.

12. The silver sintering preparation of claim 10, wherein the alkyl group C.sub.nH.sub.2n+1 of the at least one silver salt of the formula C.sub.nH.sub.2n+1COOAg is branched.

13. The silver sintering preparation of claim 12, wherein the branching is characterized by the carbon atom in position 2 carrying 2 or 3 alkyl substituents.

14. A method for the connection of electronic components, the method comprising: (a) providing a sandwich arrangement comprising at least (a1) an electronic component 1, (a2) an electronic component 2, and (a3) a silver sintering preparation according to claim 1, the silver sintering preparation situated between metal contact surfaces of the electronic components, and (b) sintering the sandwich arrangement.

15. The method of claim 14, wherein the metal contact surfaces are made of (i) a non-precious metal selected from the group consisting of copper, nickel and aluminum or of (ii) a precious metal or one of the metal contact surfaces is made of a non-precious metal selected from the group consisting of copper, nickel and aluminum and another one of the metal contact surfaces is made of a precious metal.

16. The method of claim 15, wherein the metal contact surfaces are non-precious metal contact surfaces and there is no pretreatment of the non-precious metal contact surface surfaces prior to carrying out step (b).

17. The method of claim 15, wherein the metal contact surfaces are non-precious metal contact surfaces or precious metal contact surfaces and the sintering proceeds at a temperature in a range of 200 to <300? C. with or without applying mechanical pressure and/or with or without pretreatment of the metal contact surfaces.

18. The method of claim 16, wherein at least one of the metal contact surfaces is a non-precious metal contact surface and there is no pretreatment of the at least one non-precious metal contact surface prior to carrying out step (b), and wherein step (b) is carried out in an inert atmosphere without application of mechanical pressure at a sintering temperature in a range of 200 to <300? C.

Description

EXAMPLES

1. Production of Silver Sintering Pastes:

(1) Silver sintering pastes 1 to 4 (according to the invention) and a reference paste were produced by mixing the individual ingredients according to Table 1 at comparable rheological behavior. All amounts given are in units of wt.-%.

(2) TABLE-US-00001 TABLE 1 Ref. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Silver particles.sup.1) 82 coated with 1 wt.-% stearic acid Silver particles.sup.1) 82 coated with 1 wt.-% Ag caprylate Silver particles.sup.1) 82 coated with 5 wt.-% Ag neodecanoate Silver particles.sup.1) 82 coated with 10 wt.-% Ag neodecanoate Silver particles.sup.1) 82 coated with 5 wt.-% Ag 2,4-pentanedionate Isostearic acid 2.7 2.7 2.7 2.7 2.7 Tripropylene glycol 7.2 7.2 7.2 7.2 7.2 monobutyl ether Butyl polyglycol 7.7 7.7 7.7 7.7 7.7 Ethylcellulose 0.4 0.4 0.4 0.4 0.4 Total 100 100 100 100 100 .sup.1)Silver particles having a mean particle size (d50) of 0.5 ?m

2. Application and Pressure-Free Sintering of Sintering Compositions:

(3) The respective composition was applied by means of dispensing onto the copper surface of a lead frame made of a copper-rich copper/iron alloy (96 wt.-% copper, 4 wt.-% Fe) to produce a 50 ?m thick wet layer. Then, the applied composition was contacted without previous drying to a silicon chip via its 2 mm?2 mm silver metal contact surface. The subsequent pressure-free sintering took place according to the following heating profile in a nitrogen atmosphere comprising max. 50 ppm of oxygen: The contact site was heated steadily to 250? C. over the course of 60 minutes and then maintained at 250? C. for 60 minutes. Then, the so formed arrangement was cooled steadily to 30? C. over the course of 60 minutes.

(4) After the sintering, the bonding strength was determined by shear testing. In this context, the electronic components were sheared off with a shearing chisel at a rate of 0.3 mm/s at room temperature. The force was measured by means of a load cell (DAGE 4000 plus device made by DAGE, Germany). Table 2 shows the results obtained with compositions 1 to 5.

(5) TABLE-US-00002 TABLE 2 Composition refer- Exam- Exam- Exam- Exam- ence ple 1 ple 2 ple 3 ple 4 Shear strength at 1.0 7.6 33.1 24.3 11.3 room temperature (N/mm.sup.2)