Method for joining ceramic bodies by means of an active hard solder, or braze, assembly having at least two ceramic bodies joined with one another, especially a pressure measuring cell

Abstract

An assembly, comprising: a first ceramic body and a second ceramic body connected by means of a joint of an active hard solder, or braze, wherein the active hard solder, or braze, averaged over a continuous main volume, which includes at least 50% of the volume of the joint, has an average composition C.sub.M with a liquidus temperature T.sub.l(C.sub.M). An edge region of the joint, which contacts at least one of the ceramic bodies, has an average composition C.sub.E with a liquidus temperature T.sub.l(C.sub.E), which lies not less than 20 K, preferably not less than 50 K, and especially preferably not less than 100 K above the liquidus temperature T.sub.l(C.sub.M) of the average composition C.sub.M of the main volume.

Claims

1. An assembly, comprising: a first ceramic body; and a second ceramic body, wherein: said first ceramic body and said second ceramic body are connected by means of a joint, said joint contains an active hard solder, or braze; said active hard solder, or braze, averaged over a continuous main volume, which includes at least 50% of the volume of the joint, has an average composition C.sub.M with a liquidus temperature T.sub.l(C.sub.M), wherein C.sub.M:=(c.sub.M1, . . . , c.sub.MN), wherein |C.sub.M|=1, and wherein the c.sub.Mi are the stoichiometric fractions of the components K.sub.i i=1, . . . , N of the average composition of the active hard solder, or braze, in the main volume; and an edge region of said joint, which contacts at least one of said ceramic bodies and which overlaps no more than 8% of the main volume, has an average composition C.sub.E with a liquidus temperature T.sub.l(C.sub.E), which lies not less than 20 K, above the liquidus temperature T.sub.l(C.sub.M) of the average composition C.sub.M of the main volume, wherein C.sub.E:=(c.sub.E1, . . . , c.sub.EN), wherein |C.sub.E|=1, and wherein the c.sub.Ei are the stoichiometric fractions of the components K.sub.i i=1, . . . , N of the average composition of the active hard solder, or braze, in the edge region.

2. The assembly as claimed in claim 1, wherein: the edge region with the average composition C.sub.E has a volume, which amounts to not less than 0.1% of the volume of the joint.

3. The assembly as a claimed in claim 1, wherein: said joint is ring-shaped; and the main volume is defined by a body of revolution, which is formed by rotation of a convex polygon, especially a rectangle, about the principal axis of rotation of said ring-shaped joint.

4. The assembly as claimed in claim 3, wherein: the edge region with composition C.sub.E extends along the inner edge of said ring-shaped joint.

5. The assembly as claimed in claim 1, wherein: the liquidus temperature of T.sub.l(C.sub.M) rises monotonically to the liquidus temperature T.sub.l(C.sub.E) with change of composition from C.sub.M to C.sub.E.

6. The assembly as claimed in claim 1, wherein: the composition C.sub.M has a liquidus temperature T.sub.l(C.sub.M), which lies no more than 300 K, above the liquidus temperature T.sub.l(C.sub.e) of a eutectic point, respectively of a nearest intersection with a eutectic valley with a composition C.sub.e in the composition space, wherein C.sub.e:=(c.sub.e1, . . . , c.sub.eN), wherein |C.sub.e|=1, and wherein the c.sub.ei are the stoichiometric fractions of the components K.sub.i with i=1, . . . , N at the eutectic point, respectively a nearest intersection with a eutectic valley.

7. The assembly as claimed in claim 1, wherein: an alloy of said joint has at an eutectic point, respectively at the nearest intersection with a eutectic valley in the composition space a composition C.sub.e, wherein C.sub.e :=(c.sub.e1, . . . , c.sub.eN), wherein |C.sub.e|=1, wherein the c.sub.ei are the stoichiometric fractions of the components K.sub.i with i=1, N at the eutectic point, respectively at the nearest intersection with a eutectic valley; the difference between the composition C.sub.e and the composition C.sub.M is describable with a normalized vector difference D.sub.eM, wherein: C.sub.e=C.sub.M+a.sub.eM*D.sub.eM, with |D.sub.eM|=1; and wherein the difference between the composition C.sub.E and the composition C.sub.M is describable with a normalized vector difference D.sub.EM, wherein: C.sub.E=C.sub.M+a.sub.EM*D.sub.EM, with |D.sub.EM|=1, wherein a.sub.eM and a.sub.EM are positive scalars, wherein for the scalar product S.sub.eE:=D.sub.eM.Math.D.sub.EM: S.sub.eE<0.

8. The assembly as claimed in claim 1, wherein: the composition C.sub.E of the edge region contains the same metals as the composition C.sub.M of the main volume or other metals.

9. The assembly as claimed in claim 1, wherein: said first ceramic body and/or said second ceramic body comprises Al.sub.2O.sub.3.

10. The assembly as claimed in claim 1, wherein said active hard solder, or braze, contains Zr, Ni and Ti.

11. The assembly as claimed in claim 10, wherein: the composition C.sub.M comprises 20 atom-% to 24 atom-% Ni, 13 atom-% to 17 atom-% Ti and remainder Zr, and aluminum, which diffuses in the soldering process from the ceramic into said joint; the composition C.sub.M comprises 63 atom-% Zr, 22 atom-% Ni and 15 atom-% Ti; in cases when Al is present, the titanium fraction is reduced; and the composition C.sub.E has compared with the composition C.sub.M an increased Ni fraction.

12. A pressure sensor, comprising: an assembly having a first ceramic body; and a second ceramic body, wherein: said first ceramic body and said second ceramic body are connected by means of a joint, said joint contains an active hard solder, or braze; said active hard solder, or braze, averaged over a continuous main volume, which includes at least 50%, of the volume of the joint, has an average composition C.sub.M with a liquidus temperature T.sub.l(C.sub.M), wherein C.sub.M:=(c.sub.M1, . . . ,c.sub.MN), wherein |C.sub.M|=1, and wherein the c.sub.Mi are the stoichiometric fractions of the components K.sub.i i=1, . . ., N of the average composition of the active hard solder, or braze, in the main volume; and an edge region of said joint, which contacts at least one of said ceramic bodies and which overlaps no more than 8% of the main volume, has an average composition C.sub.E with a liquidus temperature T.sub.l(C.sub.E), which lies not less than 20 K, above the liquidus temperature T.sub.l(C.sub.M) of the average composition C.sub.M of the main volume, wherein C.sub.E :=(c.sub.E1, . . . , c.sub.EN), wherein |C.sub.E|=1, and wherein the c.sub.Ei are the stoichiometric fractions of the components K.sub.i i=1, . . . , N of the average composition of the active hard solder, or braze, in the edge region; wherein: said first ceramic body is a membrane body of a measuring membrane of the pressure sensor; said second ceramic body is a platform of the pressure sensor; and said platform and said measuring membrane are joined pressure-tightly with one another by means of said joint, which is ring-shaped.

13. The pressure sensor as claimed in claim 12; further having: a capacitive transducer, wherein: a surface of said platform facing said measuring membrane and/or the surface of said measuring membrane facing said platform, have, respectively, a metal electrode; and said metal electrode comprises a metal, which is enriched in the composition C.sub.E in comparison to the composition C.sub.M.

14. The pressure sensor as claimed in claim 13, wherein: said metal, which the electrode comprises, comprises nickel.

15. A method for manufacturing an assembly, especially an assembly which comprises a first ceramic body and a second ceramic body, wherein the first ceramic body and the second ceramic body are to be joined by means of an active hard solder, or braze, the method comprises the steps of: providing the active hard solder, or braze, and a solder stop between the ceramic bodies, wherein the active hard solder, or braze, has, averaged over a continuous main volume, which includes at least 50%, 90% of the volume of the active hard solder, or braze, an average composition C.sub.M0 with a liquidus temperature T.sub.l(C.sub.M0), wherein C.sub.M0:=(c.sub.M01, . . . , c.sub.M0N), wherein |C.sub.M0|=1, and wherein the c.sub.Mi are the stoichiometric fractions of the components K.sub.i i=1, N of the average composition of the active hard solder, or braze, in the main volume, the solder stop has at least one material, whose liquidus temperature lies above the liquidus temperature of the composition C.sub.M of the main volume, and a mixing of the material of the solder stop with the composition C.sub.M leads, at least in the edge region of a joint to be formed by the method, to an average composition C.sub.E, wherein the composition C.sub.E has a liquidus temperature T.sub.l(C.sub.E), which lies not less than 20 K above the liquidus temperature T.sub.l(C.sub.M0) of the average composition C.sub.M0 of the main volume, wherein C.sub.E:=(c.sub.E1, . . . , c.sub.EN), wherein |C.sub.E|=1, and wherein the c.sub.Ei are the stoichiometric fractions of the components K.sub.i i=1, . . ., N of the average composition of the active hard solder, or braze, in the edge region; and heating the ceramic bodies, the active hard solder, or braze, and the solder stop in a vacuum soldering, brazing process, at least up to melting of the composition C.sub.M, wherein the melt in the edge region of the active hard solder, or braze, mixes with the material of the solder stop, whereby the melt in the edge region isothermally solidifies or becomes more viscous, and stops.

16. The method as claimed in claim 15, wherein: the solder stop is provided by depositing a metal or a mixture of various metals on at least one surface section of at least one ceramic body; and an enrichment of the metal or the mixture of metals in the active hard solder, or braze, leads to an increased liquidus temperature compared with the liquidus temperature of the composition of the main volume of the active hard solder, or braze.

17. The method as claimed in claim 16, wherein: the surface section of the ceramic body, in which the solder stop is provided, overlaps the contact surface between the joint and the ceramic body no more than 25%, of the contact surface between the joint and the ceramic body.

18. The assembly as claimed in claim 1, wherein: the main volume includes at least 70% of the volume of the joint.

19. The assembly as claimed in claim 1, wherein: the main volume includes at least 80% of the volume of the joint.

20. The assembly as claimed in claim 1, wherein: the edge region overlaps no more than 4% of the main volume.

21. The assembly as claimed in claim 1, wherein: the edge region overlaps no more than 2% of the main volume.

22. The assembly as claimed in claim 1, wherein: the edge region lies outside of the main volume.

23. The assembly as claimed in claim 1, wherein: the composition C.sub.E of the edge region has a liquidus temperature T.sub.l(C.sub.E), which lies not less than 50 K above the liquidus temperature T.sub.l(C.sub.M) of the average composition C.sub.M of the main volume.

24. The assembly as claimed in claim 1, wherein: the composition C.sub.E of the edge region has a liquidus temperature T.sub.l(C.sub.E), which lies not less than 100 K above the liquidus temperature T.sub.l(C.sub.M) of the average composition C.sub.M of the main volume.

25. The assembly as claimed in claim 1, wherein: the edge region with the average composition C.sub.E has a volume, which amounts to not less than 0.5% of the volume of the joint.

26. The assembly as claimed in claim 1, wherein: the edge region with the average composition C.sub.E has a volume, which amounts to not less than 1% of the volume of the joint.

27. The assembly as claimed in claim 15, wherein: the composition C.sub.M has a liquidus temperature T.sub.l(C.sub.M), which lies no more than 150 K above the liquidus temperature T.sub.l(C.sub.e) of said eutectic point, respectively of said nearest intersection with said eutectic valley.

28. The assembly as claimed in claim 15, wherein: the composition C.sub.M has a liquidus temperature T.sub.l(C.sub.M), which lies no more than 50 K above the liquidus temperature T.sub.l(C.sub.e) of said eutectic point, respectively of said nearest intersection with said eutectic valley.

29. The assembly as claimed in claim 18, wherein: s.sub.eE<0.5.

30. The assembly as claimed in claim 18, wherein: s.sub.eE<0.8.

31. The assembly as claimed in claim 24, wherein: the composition C.sub.M comprises 63 atom-% Zr, 22 atom-% Ni and 15 atom-% Ti.

32. The assembly as claimed in claim 23, wherein: the composition C.sub.M comprises 20 atom-% to 24 atom-% Ni, 13 atom-% to 17 atom-% Ti and remainder Zr, as well as, aluminum, which diffuses in the soldering process from the ceramic into said joint.

33. The assembly as claimed in claim 26, wherein: the composition C.sub.M comprises 63 atom-% Zr, 22 atom-% Ni and 15 atom-% Ti; the titanium fraction is reduced; and the composition C.sub.E has compared with the composition C.sub.M an increased Ni fraction.

34. The pressure sensor as claimed in claim 28, wherein: said average composition C.sub.M of said active hard solder, or braze is averaged over a continuous main volume, which includes at least 70% of the volume of the joint.

35. The pressure sensor as claimed in claim 28, wherein: said average composition C.sub.M of said active hard solder, or braze is averaged over a continuous main volume, which includes at least 80% of the volume of the joint.

36. The pressure sensor as claimed in claim 28, wherein: said edge region of said joint overlaps no more than 4% of the main volume.

37. The pressure sensor as claimed in claim 28, wherein: said edge region of said joint overlaps no more than 2% of the main volume.

38. The pressure sensor as claimed in claim 28, wherein: said edge region of said joint lies outside of the main volume.

39. The pressure sensor as claimed in claim 28, wherein: said edge region of said joint has an average composition C.sub.E with a liquidus temperature Tl(C.sub.E), which lies not less than 50 K above the liquidus temperature T.sub.l(C.sub.M) of the average composition C.sub.M of the main volume.

40. The pressure sensor as claimed in claim 28, wherein: said edge region of said joint has an average composition C.sub.E with a liquidus temperature Tl(C.sub.E), which lies not less than 100 K above the liquidus temperature Tl(C.sub.M) of the average composition C.sub.M of the main volume.

41. The method as claimed in claim 38, wherein: the active hard solder, or braze, has, averaged over a continuous main volume, which includes at least 70% and preferably of the volume of the active hard solder, or braze, said average composition C.sub.M0.

42. The method as claimed in claim 38, wherein: the active hard solder, or braze, has, averaged over a continuous main volume, which includes at least 90% and preferably of the volume of the active hard solder, or braze, said average composition C.sub.M0.

43. The method as claimed in claim 38, wherein: the composition C.sub.E has a liquidus temperature T.sub.l(C.sub.E), which lies not less than 50 K above the liquidus temperature T.sub.l(C.sub.M0) of the average composition C.sub.M0 of the main volume.

44. The method as claimed in claim 38, wherein: the composition C.sub.E has a liquidus temperature T.sub.l(C.sub.E), which lies not less than 100 K above the liquidus temperature Tl(C.sub.M0) of the average composition C.sub.M0 of the main volume.

45. The method as claimed in claim 44, wherein: the surface section of the ceramic body, in which the solder stop is provided, overlaps the contact surface between the joint and the ceramic body no more than 10% of the contact surface between the joint and the ceramic body.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be explained based on the example of an embodiment illustrated in the drawing, the figures of which show as follows:

(2) FIG. 1 is a section through an example of a phase diagram for a binary alloy;

(3) FIG. 2 is a longitudinal section through a pressure measuring cell of the invention;

(4) FIG. 3a is a composition distribution C(r) before the melting of the alloy of the active hard solder, or braze; and

(5) FIG. 3b is a composition distribution C(r) after the joining process.

DETAILED DISCUSSION IN CONJUNCTION WITH THE DRAWINGS

(6) As shown in FIG. 1, an alloy, which is composed of a mixture of two metals or two alloys A and B, has a eutectic point, respectively an intersection with a eutectic valley, at a composition C.sub.e. In the vicinity of this composition C.sub.e, a composition C.sub.M0 has, compared with C.sub.e, a somewhat increased amount of component B, which, compared with the composition C.sub.e, has an only slightly increased liquidus temperature. A further enrichment of the component B leads to a significantly increased liquidus temperature, such as, for example, indicated for the composition C.sub.E.

(7) Starting from these considerations, the components of a pressure measuring cell will be joined. The arrangement of the components before joining are presented in FIG. 2. The pressure measuring cell includes a ceramic platform 1 and a measuring membrane 2, both of which comprise aluminum oxide. The measuring membrane 2 and the platform are to be joined by means of an active hard solder, or braze. In order to keep the active hard solder, or braze, in a defined region, there is deposited on a surface of the platform 1 facing the measuring membrane 2, for example, by sputtering, an annular solder stop 3 which has, for example, a radial dimension r.sub.i-r.sub.s of, for instance, 0.5 mm. The coating thickness of the solder stop amounts to, for example, 0.1 m to 0.5 m. The solder stop can especially comprise nickel. A corresponding solder stop 4 is deposited on a surface of the measuring membrane 2 facing the platform 1, wherein the membrane-side solder stop 4 on the measuring membrane 2 especially can be formed as a full surface, circular disk, in order therewith at the same time to serve as a membrane-side electrode of a capacitive transducer. Also, the membrane-side solder stop 4 can comprise nickel in a thickness of, for example, 0.1 m to 0.5 m.

(8) During the preparation of the solder stop 3 on the platform, at the same time, at least one platform-side measuring electrode 6 of the capacitive transducer can be deposited. Especially, measuring electrode 6 is of the same material as the solder stop 4. The platform-side measuring electrode 6 should, however, be galvanically isolated from the platform-side solder stop 4.

(9) For preparing the connection, then an active hard solder, or braze, ring 5 is provided between the platform and the measuring membrane, which extends outwards from r.sub.i to r.sub.a. Ring 5 comprises, for example, a ternary ZrNiTi active hard solder, or braze, having a composition C.sub.M0 of especially 63 atom-% Zr, 22 atom-% Ni and 15 atom-% Ti. This hard solder, or braze, has a liquidus temperature T.sub.l(C.sub.M0) of, for instance, 870 C. With reference to FIG. 1, the sub composition of Zr and Ti is considered to be component A, while Ni is component B. The composition C(r) of the metal components on the surface of the platform before the melting of the active hard solder, or braze, is shown as a function of radius in FIGS. 3a and 3b. In the region of the solder stop of Ni, accordingly exclusively present is the component B, while in the region of the ring of active hard solder, or braze, a mixture of A and B is present as the composition C.sub.M0. After heating of the arrangement of FIG. 2 in a high vacuum soldering process to a soldering, brazing temperature of, for instance, 890 C., the active hard solder, or braze, ring 5 melts, and its active component Ti reacts with the ceramic material of the measuring membrane and of the platform. At the same time, at the interface between the active hard solder, or braze, and the solder stop, nickel from the solder stop migrates into the melt, wherein through local enrichment of nickel there arises in the edge region a composition C.sub.E, whose liquidus temperature T.sub.l(C.sub.E) lies above the current soldering temperature. Thereupon, the melt in the edge region solidifies, whereby a further inflowing of the active hard solder, or braze, is reliably prevented. Actually, as a result of the soldering process aluminum from the ceramic can diffuse both into the main volume as well as also into the edge region, while titanium from the active hard solder, or braze, diffuses into the ceramic, so that the composition C.sub.E of the edge region can furthermore contain Al in addition to the metals of the solder stop and of the active hard solder, or braze, whereby the composition C.sub.M of the main volume can additionally contain after the soldering, besides the elements in the composition C.sub.M0 of the active hard solder or braze before the soldering, also aluminum.