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