Solder material, method for the production thereof and use thereof to join metal substrates without pressure

Abstract

The invention relates to a silver solder paste and to a silver solder paste containing copper, which can be used to join metal or metalized substrates, in particular copper substrates, without pressure at low temperatures. The silver solder according to the invention contains a metal-organic silver complex as a precursor, which forms silver nanoparticles only upon being heated and which forms a silver-metal molten phase over a temperature range of 20 to 40 units upon being heated further, which silver-metal molten phase can be used as a process window for joining already starting at 150 C., preferably starting at approximately 200 C.

Claims

1. A solder material containing A) a metal-organic silver precursor which forms silver nanoparticles at temperatures below 200 C. and has a metal molten phase over a temperature range of at least 20-40 K wherein the metal-organic silver precursor is silver(I)-2-[2-(2-methoxyethoxy)ethoxy]acetate or a primary or secondary silver alkylamine having 8-12 carbon atoms; B) 25-150% by weight, based on the weight of the silver precursor A), of uncoated and agglomerated silver particles with an average particle diameter of the agglomerates of 100-250 nm, which can be completely fused with the metal molten phase of the silver precursor A); and C) a precursor comprising a copper-organic complex which forms nanoparticles upon being heated, wherein the copper-organic complex C) is a primary or secondary copper (II) alkanoate having 8-12 carbon atoms, and wherein a ratio of the silver precursor A) to the precursor C) is 1:0.3 to 1:0.7, when the solder material is a paste which contains so much alcohol that it is easy to spread or wherein a ratio of the silver precursor A) to the precursor C) is 1:0.15 to 1:0.5, when the solder material does not contain any alcohol, but the solder material is a powder.

2. The solder material according to claim 1, wherein the metal-organic silver precursor A) is silver(I)-2-[2-(2-methoxyethoxy)ethoxy]acetate.

3. The solder material according to claim 1, wherein the alcohol is a C.sub.1-C.sub.4 alcohol.

4. The solder material according to claim 1, wherein the paste obtained is heated under argon as an inert gas at 7 to 8 C. per minute to above the sintering temperature.

5. A method of using a solder material according to claim 1 to join at least two metal or metalized substrates provided for bonding without pressure, wherein the solder material is placed as a spreadable paste or compactable or compacted powder between the substrates to be joined, the alcohol is optionally evaporated and the substrates to be joined with the solder material are directly heated to a joining temperature in the range of 150-250 C. and sintered at this temperature, as a result of which elementary silver is formed between the contact surfaces.

6. The method according to claim 5, wherein the substrates to be joined are sintered with the applied solder material at a joining temperature in the range of 200 C. to 250 C.

7. The method according to claim 5 wherein the holding time on joining, as a function of the size of the substrates to be joined, is between 3 and 30 minutes.

8. The method according to claim 5, wherein the substrates to be joined are sintered with the applied solder material at a joining temperature in the range of >220 C. to 250 C.

9. The solder material of claim 1, wherein the precursor C) further comprises a silver-organic complex which forms nanoparticles upon being heated, wherein the silver-organic complex is a primary or secondary silver(I) alkanoate having 8-12 carbon atoms.

Description

(1) The invention will be explained in more detail below by means of exemplary embodiments, but without limiting it to these, wherein

(2) FIG. 1 shows the temperature behavior of the paste according to Example 1.

(3) FIGS. 2A, 2B, 2C and 2D show manifestations of a silver precursor drop (diameter approx. 10 mm) as the temperature increases: a) and b) formation of red nanoparticles in the (yellow) liquid phase at 140-145 C.; c) silver-metal-molten phase at 190 C.; d) degassing of the organic components at 230 C.;

(4) FIG. 3 shows a SEM image of a silver solder between copper parts, produced at 250 C., holding time of 1 hour;

(5) FIG. 4 shows an enlarged section of FIGS. 2A-2D;

(6) FIG. 5 shows a SEM image of a silver solder with a higher copper content between copper, produced at 250 C., holding time of 1 hour. The distribution of silver and copper in the layer is shown by the line scan.

EXAMPLE 1

(7) Preparation of Solder Materials According to the Invention with silver(I)-2-[2-(2-methoxyethoxy)ethoxy]acetate as the Silver Precursor

(8) Preparation of the Silver Precursor A):

(9) 10 g of silver nitrate (59 mmol) are dissolved in 8 ml of acetonitrile and added to 100 ml of ethanol. A mixture consisting of 13.36 g (11.5 ml, 75 mmol) of the corresponding acid 2-[2-(2-methoxyethoxy)ethoxy]acetic acid, 9.0 ml (6.57 g, 65 mmol) of triethylamine and 100 ml of ethanol is slowly added to this mixture and stirred. After 15 minutes of stirring and standing for 2 hours, the reaction product is cooled in an ice bath for 2 hours, during which time a precipitate is formed. This is filtered off and washed successively with ethanol and acetone.

(10) Preparation of the Silver Precursor C):

(11) The foregoing method is the same for the production of silver decanoate:

(12) 10 g of silver nitrate (in 8 ml of acetonitrile and 100 ml ethanol) and 12.92 g (75 mmol) of decanoic acid with 9.0 ml (65 mmol) of triethylamine and 150 ml of ethanol.

(13) and copper decanoate:

(14) 10.0 g (74 mmol) of copper(II) chloride (in 10 ml. of distilled water and 100 ml of ethanol), and 25.84 g (150 mmol) of decanoic acid with 18.0 ml (130 mmol) of triethylamine and 150 ml of ethanol.

(15) Preparation of the Silver Particles B):

(16) 3.03 g (80 mmol) of sodium borhydride are dissolved in 300 ml of distilled water and cooled in an ice bath for 30 minutes with stirring. Thereafter, 6.8 g (40 mmol) of silver nitrate, dissolved in 50 ml distilled water, are slowly dropped into this solution. The precipitate thus formed is filtered off and successively washed with ethanol and acetone.

(17) a) A powder with the following proportions, based on the silver precursor A), is produced from the produced components A), B) and C):

(18) Precursor A: silver particles B=1:0.7

(19) Precursor A: precursor C=1:0.1

(20) FIGS. 3 and 4 show the SEM image of the silver layer produced with this powder.

(21) b) A powder with the produced components A), B) and C) was produced with the following proportions:

(22) Precursor A: silver particles B=1:0.4

(23) Precursor A: copper precursor C=1:0.5

EXAMPLE 2

(24) Joining of Copper Substrates with the Powder in Accordance with Example 1:

(25) Preparation of the substrates: It was guaranteed that the surfaces were degreased by cleaning the copper parts in an ultrasonic bath with ethanol. The copper surfaces were then etched in citric acid in the conventional manner.

(26) The easily compressible solder material was applied to the lower part of the prepared surfaces to be joined and the joining upper part was lightly pressed on, so that a complete contact between the joining material and the upper part could be assumed. The parts were then heated directly to the joining temperature of 250 C. Since the samples were made of solid copper parts, a holding time of 30 minutes at 250 C. was selected despite the good thermal conductivity of the copper base material. The samples were removed from the furnace and left to cool to room temperature.

(27) As the powder contains the copper precursor C), the sample was placed in a furnace which can be operated under a blanket of nitrogen, in order to avoid oxidation effects of the copper precursor in the air.

(28) FIG. 5 shows the SEM image of the layer produced with this copper-containing silver powder.