Method of joining using reactive multilayer foils with enhanced control of molten joining materials
In accordance with the invention, bodies of materials are joined by disposing between them a reactive multilayer foil and one or more layers of meltable joining material such as braze or solder. The bodies are pressed together against the foil and joining material, and the foil is ignited to melt the joining material. The pressing is near the critical pressure and typically produces a joint having a strength of at least 70-85% the maximum strength producible at practical maximum pressures. Thus for example, reactively formed stainless steel soldered joints that were heretofore made at an applied pressure of about 100 MPa can be made with substantially the same strength at a critical applied pressure of about 10 kPa. Advantages of the process include minimization of braze or solder extrusion and reduced equipment and processing costs, especially in the joining of large bodies.
1 . A method of joining first and second bodies of material using a reactive multilayer foil and one or more layers or coatings of meltable joining material comprising the steps of:
disposing the reactive foil and meltable joining material between the bodies;
pressing the bodies together against the foil and the joining material; and
initiating a self-propagating reaction through the foil to melt the joining material,
wherein a joining strength versus applied pressure plot for the joining process is characterized by a lower applied pressure region with a relatively high slope, a higher applied pressure region with a relatively low slope, and a knee region between the high slope and low slope, and wherein the bodies are pressed together at a pressure in the knee region.
2 . The method of claim 1 wherein the pressure is about 30 kPa or less.
3 . The method of claim 1 wherein the pressure is about 20 kPa or less.
4 . The method of claim 1 wherein the meltable joining material comprises solder or braze material.
5 . The method of claim 1 wherein the pressure is sufficiently low that the thickness of the joining materials is reduced by no more than 20% by the joining process.
6 . The method of claim 1 wherein the melting of the joining materials has a duration greater that about 0.5 ms.
7 . The method of claim 1 wherein the joining material has a thickness greater than about 0.5 micrometers.
8 . The method of claim 1 wherein the bodies of material are joined over an area exceeding about 0.03 cm 2 .
9 . The method of claim 1 wherein the strength of the joint exceeds about 1 MPa.
10 . The method of claim 1 wherein the joint has an area greater than about 10 in 2 .
11 . A method of joining first and second bodies of material using reactive multilayer foil and one or more layers or coatings of meltable joining material comprising the steps of:
disposing the reactive foil and the meltable joining material between the bodies;
pressing the bodies together against the foil and the joining material; and
initiating a self-propagating reaction through the foil to melt the joining material;
wherein the pressing is at a pressure substantially less than the maximum practical applied pressure that does not damage the bodies but provides a joint having a shear strength equal to at least 70% of the shear strength at the maximum practical applied pressure.
12 . The method of claim 11 wherein the pressure is about 30 kPa or less.
13 . The method of claim 11 wherein the pressure is about 20 kPa or less.
14 . The method of claim 11 wherein the meltable joining material comprises solder or braze material.
15 . The method of claim 11 wherein the pressure is sufficiently low that the thickness of the joining materials is reduced by no more than 20% by the joining process.
16 . The method of claim 11 wherein the melting of the joining materials has a duration greater that about 0.5 ms.
17 . The method of claim 11 wherein the joining material has a thickness greater than about 0.5 micrometers.
18 . The method of claim 11 wherein the bodies of material are joined over an area exceeding about 0.03 cm 2 .
19 . The method of claim 11 wherein the strength of the joint exceeds about 1 MPa.
20 . The method of claim 11 wherein the joint has an area greater than about 10 in 2 .
21 . A method of joining first and second bodies of material using reactive multilayer foil and one or more layers or coatings of meltable joining material comprising the steps of:
disposing the reactive foil and the meltable joining material between the bodies;
pressing the bodies together against the foil and the joining material; and
initiating a self-propagating reaction through the foil to melt the joining material;
wherein the pressing is at a pressure substantially less than 100 MPa but provides a joint having a shear strength equal to at least 70% of the shear strength formed using an applied pressure of 100 MPa.
22 . The method of claim 21 wherein the pressure is about 30 kPa or less.
23 . The method of claim 21 wherein the pressure is about 20 kPa or less.
24 . The method of claim 21 wherein the meltable joining material comprises solder or braze material.
25 . The method of claim 21 wherein the pressure is sufficiently low that the thickness of the joining materials is reduced by no more than 20% by the joining process.
26 . The method of claim 21 wherein the melting of the joining materials has a duration greater that about 0.5 ms.
27 . The method of claim 21 wherein the joining material has a thickness greater than about 0.5 micrometers.
28 . The method of claim 21 wherein the bodies of material are joined over an area exceeding about 0.03 cm 2 .
29 . The method of claim 21 wherein the strength of the joint exceeds about 1 MPa.
30 . The method of claim 21 wherein the joint has an area greater than about 10 in 2 .
31 . A method of joining first and second bodies of material using reactive multilayer foil and one or more layers or coatings of meltable joining material comprising the steps of:
disposing the reactive foil and the meltable joining material between the bodies;
pressing the bodies together against the foil and the joining material; and
initiating a self-propagating reaction through the foil to melt the joining material;
wherein at least one of the first and second bodies comprises a microcircuit device or a semicondutor and the pressing is at a pressure low enough to eliminate solder spray from the joint but high enough to form a joint having a shear strength equal to at least 70% of the shear strength of the solder or braze material used to form the joint.
32 . The method of claim 31 wherein the pressure is about 30 kPa or less.
33 . The method of claim 31 wherein the pressure is about 20 kPa or less.
34 . The method of claim 31 wherein the meltable joining material comprises solder or braze material.
35 . The method of claim 31 wherein the pressure is sufficiently low that the thickness of the joining materials is reduced by no more than 20% by the joining process.
36 . The method of claim 31 wherein the melting of the joining materials has a duration greater that about 0.5 ms.
37 . The method of claim 31 wherein the joining material has a thickness greater than about 0.5 micrometers.
38 . The method of claim 31 wherein the bodies of material are joined over an area exceeding about 0.03 cm 2 .
39 . The method of claim 31 wherein the strength of the joint exceeds about 1 MPa.
40 . A product comprising at least two bodies of material joined by the process of claim 1 .
41 . A product comprising at least two bodies of material joined by the process of claim 11 .
42 . A product comprising at least two bodies of material joined by the process of claim 21 .
43 . A product comprising at least two bodies of material joined by the process of claim 31.