Brazing method for assembling two elements via an intermetallic compound

Abstract

A brazing method for assembling two elements includes selecting two brazing materials that can generate, when they are heated and melted, an intermetallic compound having a melting temperature which is higher than the melting temperature of each of the selected brazing materials taken individually, positioning the two selected brazing materials between the two elements, heating and melting the two selected brazing materials in order to substantially reach the melting temperature of each of the selected brazing materials so as to achieve the precipitation of an intermetallic compound having a melting temperature which is higher than the melting temperature of each of the selected brazing materials taken individually.

Claims

1. A brazing method for assembling two elements, said method comprising: selecting two brazing materials that can generate, when the two brazing materials are heated and melted, an intermetallic compound having a melting temperature which is higher than the melting temperature of each of the two selected brazing materials taken individually, positioning the two selected brazing materials between the two elements, heating and melting the two selected brazing materials to substantially reach the melting temperature of each of the two selected brazing materials so as to achieve the precipitation of an intermetallic compound having a melting temperature which is higher than the melting temperature of each of the two selected brazing materials taken individually.

2. The brazing method according to claim 1, wherein each of the two selected brazing materials is an alloy or a pure metal.

3. The brazing method according to claim 1, wherein one of the two selected brazing materials is Au80Sn20 alloy and the other of the two selected brazing materials is pure tin.

4. The brazing method according to claim 1, wherein each of the two selected brazing materials is in the form of: a strip, or a powder mixed with an organic material.

5. The brazing method according to claim 4, wherein the organic material plays the role of deoxidising agent.

6. The brazing method according to claim 4, wherein the powder mixed with the organic material is positioned between the two elements using a syringe.

7. The brazing method according to claim 1, wherein one of the two elements is formed by a substrate and the other of the two elements is formed by an electronic component.

8. The brazing method according to claim 1, wherein the difference between each of the two melting temperatures of the two selected brazing materials and the melting temperature of the intermetallic compound is higher than 100 C.

9. A device comprising two elements attached to each other, said two elements being attached to each other via an intermetallic compound obtained via the melting of two brazing materials, said intermetallic compound having a melting temperature which is higher than the melting temperature of each of the two brazing materials.

Description

(1) Other characteristics and advantages of the invention will become clear from the description that is given thereof hereafter, by way of indication and in no way limiting, with reference to the appended figures among which:

(2) FIG. 1 illustrates a synoptic of the steps of the method in accordance with the invention;

(3) FIG. 2 illustrates a tin and gold binary phase change diagram;

(4) FIG. 3 illustrates in a schematic manner an exemplary embodiment of a device in accordance with the invention.

(5) For reasons of clarity, only elements useful for understanding the invention have been represented, without respect for scale and in a schematic manner. Moreover, similar elements located in the different figures bear identical references.

(6) FIG. 1 illustrates the steps of the brazing method 100 for assembling two elements in accordance with the invention. In a non-limiting manner, the two elements are formed by a first element of substrate type and a second element of electronic component type, such as an electronic chip.

(7) The brazing method 100 comprises a step 101 of selecting two brazing materials that can generate, when they are heated and melted, an intermetallic compound having a melting temperature which is higher than the melting temperature of each of the selected materials taken individually.

(8) It should be noted that each selected brazing material is an alloy or a pure metal. As a non-limiting example, it is possible to select a first brazing material of pure metal type, for example pure tin, the melting temperature of which is 232 C. Moreover, it is possible to select a second brazing material of alloy type, for example the alloy Au80Sn20, the melting temperature of which is 278 C. After having heated and melted the pure tin and the Au80Sn20 alloy, the intermetallic compound obtained will be an alloy of AuSn type, the melting temperature of which is 419 C.

(9) For example, FIG. 2 illustrates a tin-gold binary phase change diagram. As an example, if the two elements attached via the intermetallic compound have to be implemented in an operating environment, such as an aircraft engine, close to 300 C., then an intermetallic compound is required of which the melting temperature is distinctly higher than 300 C. With regard to the tin-gold binary phase change diagram illustrated in FIG. 2, it is advantageous to select the intermetallic compound formed by the alloy AuSn, the melting temperature of which is 419.3 C. By choosing the intermetallic compound AuSn, the melting temperature of which is 419.3 C., the intermetallic compound is formed of an alloy having 62.5% by weight of gold and 37.5% by weight of tin. Thus, in a non-limiting manner, to obtain the intermetallic compound formed of an alloy having 62.5% by weight of gold and 37.5% by weight of tin, it is possible to use: A first brazing material formed by the alloy Au80Sn20, the melting temperature of which is 278 C. and the weight represents 72% by weight of the intermetallic compound, this alloy Au80Sn20 comprises 20% by weight of tin+80% by weight of gold, and A second brazing material formed by pure tin having a melting temperature of 232 C. and the weight of which represents 28% of the intermetallic compound.

(10) The fact of heating and melting this association makes it possible to obtain an alloy of 62.5% by weight of gold+37.5% by weight of tin, i.e. the precise proportion of the intermetallic compound AuSn.

(11) The brazing method 100 further comprises a step of positioning 102 the two selected brazing materials between the two elements.

(12) Each of the two aforementioned brazing materials may be in the form of: a preform (also designated strip), or a powder mixed in a homogenous manner with a high viscosity organic material (commonly called brazing cream), the high viscosity organic material playing the role of deoxidising agent.

(13) For example, when one or the two brazing materials is (are) in the form of powder mixed with a high viscosity organic material, it may be positioned between the two elements using a syringe.

(14) The brazing method 100 also comprises a step 103 consisting in heating and melting the selected brazing materials in order to substantially reach the melting temperature of each of the selected brazing materials so as to achieve the precipitation of an intermetallic compound having a melting temperature which is higher than the melting temperature of each of the selected materials taken individually.

(15) According to the example described, it is thus possible by heating around 309 C. to reach the melting temperature of the two selected brazing materials so as to melt them (in other words to mix them) in order to create a pure intermetallic compound having a melting temperature of 419 C. Thus, the temperature of the brazing method has not exceeded 309 C., which makes it possible to preserve all of the electronic components located on the substrate. All the same, the substrate and the electronic chip could be positioned in an environment of which the nominal operating temperature exceeds 309 C. without for all that risking being detached from each other.

(16) In other words, the present invention consists in a brazing solution making it possible to assemble two elements, thanks to the melting of two metals or alloys of metals, at a temperature enabling the precipitation of a single intermetallic compound, having a melting point higher than the melting temperatures of the starting two metals or metal alloys. In other words, the method 100 according to the invention makes it possible to obtain a brazing joint 100% composed of an intermetallic compound which is very stable over time, unlike the complex metallographic associations that are generally found in brazing alloys.

(17) The invention also pertains to a device 1 in accordance with the invention comprising two elements 2 and 3 attached to each other. FIG. 3 illustrates such a device 1.

(18) A first element is formed by an electronic chip 2 and a second element is formed by a substrate 3, the electronic chip 2 and the substrate 3 being attached to each other via an intermetallic compound 4 obtained via the melting of two brazing materials. The intermetallic compound 4 has a melting temperature which is higher than the melting temperature of each of the two amalgamated brazing materials.