METHOD OF JOINING A NIOBIUM TITANIUM ALLOY BY USING AN ACTIVE SOLDER

Abstract

There is provided a method of joining a first member made of a niobium titanium alloy to a second member. The method comprises abutting a respective surface of each of the first member and the second member together to form an interface therebetween; providing a molten active solder at a surface of at least the first member at the interface and thermally activating the molten active solder; mechanically agitating the molten active solder so as to cause the molten solder to adhere to the first and second members and form a continuous body of molten solder linking the first and second; and causing the continuous body to solidify thereby forming a solder joint between the first and second members.

Claims

1-23. (canceled)

24. A method of joining a first member made of a niobium titanium alloy to a second member, the method comprising: abutting a respective surface of each of the first member and the second member together to form an interface therebetween; providing a molten active solder at a surface of at least the first member at the interface and thermally activating the molten active solder; mechanically agitating the molten active solder so as to cause the molten solder to adhere to the first and second members and form a continuous body of molten solder linking the first and second; and causing the continuous body to solidify thereby forming a solder joint between the first and second members.

25. The method according to claim 24, wherein the molten active solder is provided at the surface of at least the first member and thermally activated before the respective surfaces of each of the first and second member are abutted together, the thermally activated molten solder being mechanical agitated at the surface of the first member so as to cause the active solder to adhere to the surface of the first member thereby providing a coated surface of the first member.

26. The method according to claim 25, further comprising causing the molten active solder to solidify between providing the coated surface of the first member and abutting the respective surfaces of each of the first and second members, and re-melting the active solder after abutting said respective surfaces.

27. The method according to claim 25, wherein further molten active solder is provided at the respective surfaces of the first and second members when said surfaces are abutted.

28. The method according to claim 25, further comprises coating a surface of the second member with tin or a tin solder alloy.

29. The method according to claim 28, wherein coating the surface of the second member with tin or a tin solder alloy comprises electroplating the surface of the second member with tin or tin solder alloy or comprises providing molten tin or tin solder alloy at the surface of the second member.

30. The method according to claim 25, further comprising providing molten active solder at the surface of the second member and mechanically agitating the molten solder so as to cause the solder to adhere to the surface of second member thereby providing a coated surface of the second member.

31. The method according to claim 30, wherein the active solder provided as molten solder at the surface of the second member is the same active solder as the active solder coated on the surface of the first member, and/or further comprising causing the molten solder provided at the surface of the second member to solidify between the step of providing the coated surface of the second member and the step of abutting the respective surfaces of each of the first and second members, and re-melting the second solder after abutting said respective surfaces.

32. The method according to claim 24, further comprising warming the respective surfaces of the first and second members to a temperature below the melting temperature of the active solder while the surfaces are abutted.

33. The method according to claim 24, wherein mechanical agitation is provided by use of ultrasound to induce mechanical movement in the molten active solder.

34. The method according to claim 24, wherein the mechanical agitation provided when the respective surfaces of the first and second members are abutted is provided at least in part by movement of said respective surfaces against each other.

35. The method according to claim 34, wherein the movement of said respective surfaces against each other is relative rotational movement.

36. The method according to claim 24, wherein the active solder is an alloy including tin and at least one of silver, titanium, cerium, gallium and magnesium.

37. The method according to claim 24, wherein the providing of the molten active solder and thermally activating the molten active solder at the surface of at least the first member is performed after the respective surfaces of each of the first member and second member are abutted together thereby providing the molten active solder and thermal activation of the molten active solder at the interface of the first and second members.

38. A method of joining a first member made of a niobium titanium alloy to a second member, the method comprising: providing a thermally activated molten active solder at a surface of the first member and mechanically agitating the thermally activated active solder so as to cause the active solder to adhere to the surface of first member thereby providing a coated surface of the first member; abutting the first member and the second member together and mechanically agitating the molten active solder causing the molten active solder to adhere to a surface of the second member so as to form a continuous body of molten solder linking the surfaces of the first and second members; and causing the continuous body to solidify thereby forming a solder joint between the first and second members.

39. The method according to claim 38, further comprising causing the molten active solder to solidify between providing the coated surface of the first member and abutting the respective surfaces of each of the first and second members, and re-melting the active solder after abutting said respective surfaces.

40. The method according to claim 38, wherein further molten active solder is provided at the respective surfaces of the first and second members when said surfaces are abutted.

41. The method according to claim 38, further comprising coating a surface of the second member with tin or a tin solder alloy.

42. The method according to claim 41, wherein coating the surface of the second member with tin or a tin solder alloy comprises electroplating the surface of the second member with tin or tin solder alloy or comprises providing molten tin or tin solder alloy at the surface of the second member.

43. The method according to claim 38, further comprising providing molten active solder at the surface of the second member and mechanically agitating the molten solder so as to cause the solder to adhere to the surface of second member thereby providing a coated surface of the second member.

44. The method according to claim 43, wherein the active solder provided as molten solder at the surface of the second member is the same active solder as the active solder coated on the surface of the first member and/or further comprising causing the molten solder provided at the surface of the second member to solidify between the step of providing the coated surface of the second member and the step of abutting the respective surfaces of each of the first and second members, and re-melting the second solder after abutting said respective surfaces.

45. The method according to claim 38, further comprising warming the respective surfaces of the first and second members to a temperature below the melting temperature of the active solder while the surfaces are abutted.

46. The method according to claim 38, wherein mechanical agitation is provided by use of ultrasound to induce mechanical movement in the molten active solder.

47. The method according to claim 38, wherein the mechanical agitation provided when the respective surfaces of the first and second members are abutted is provided at least in part by movement of said respective surfaces against each other.

48. The method according to claim 47, wherein the movement of said respective surfaces against each other is relative rotational movement.

49. The method according to claim 38, wherein the active solder is an alloy including tin and at least one of silver, titanium, cerium, gallium and magnesium.

50. A method of joining a first member made of a niobium titanium alloy to a second member, the method comprising: abutting the first member and the second member together to form an interface therebetween; providing a molten active solder at the interface of the first and second members and thermally activating the molten active solder; mechanically agitating the thermally activated molten active solder causing the molten solder to adhere to the first and second members and form a continuous body of molten solder linking the first and second members; and causing the continuous body to solidify thereby forming a solder joint between the first and second members.

51. The method according to claim 50, further comprising warming the respective surfaces of the first and second members to a temperature below the melting temperature of the active solder while the surfaces are abutted.

52. The method according to claim 50, wherein mechanical agitation is provided by use of ultrasound to induce mechanical movement in the molten active solder.

53. The method according to claim 50, wherein the mechanical agitation provided when the respective surfaces of the first and second members are abutted is provided at least in part by movement of said respective surfaces against each other.

54. The method according to claim 53, wherein the movement of said respective surfaces against each other is relative rotational movement.

55. The method according to claim 50, wherein the active solder is an alloy including tin and at least one of silver, titanium, cerium, gallium and magnesium.

56. Use of an active solder in forming a solder joint between a two members, at least one member being made of a niobium titanium alloy.

57. The active solder according to claim 56, wherein the active solder is an alloy including tin and silver and at least one of titanium, cerium, gallium and magnesium.

Description

BRIEF DESCRIPTION OF FIGURES

[0051] Examples of a joining method are described in detail below, with reference to the accompanying figures, in which:

[0052] FIG. 1 shows a flow chart of an example joining method;

[0053] FIG. 2 shows a flow chart of a sub-process of the example joining method of FIG. 1;

[0054] FIG. 3 shows a flow chart of a second sub-process of the example joining method of FIG. 1;

[0055] FIG. 4 shows a flow chart of a second example joining method; and

[0056] FIG. 5 shows a flow chart of an application of the example joining method of FIG. 1.

DETAILED DESCRIPTION

[0057] We now describe two examples of a joining method, along with a description of an example application of one of the example joining methods.

[0058] Referring now to FIG. 1, a process of a first example joining method is illustrated generally at 1.

[0059] The process illustrated in FIG. 1 is a two-stage process. The first stage of this process is to coat a surface of a first member made of a niobium titanium alloy with an active solder, step 10, and coat a surface of a second member each with a solder, step 11. This is commonly referred to as tinning.

[0060] The process carried out to coat the surface of the first member is illustrated generally at 100 in FIG. 2. This process involves heating the active solder to a joining temperature of the active solder, step 101. The joining temperature, which as is explained below, is a higher temperature than the melting temperature of the solder, and is a temperature at which the reactivity of the reactive elements is sufficiently high for them to react with oxides with which the solder comes into contact. This is referred to as thermal activation of the active solder.

[0061] When the active solder is molten, the solder and the reactive elements in the solder quickly oxidise on contact with air. The oxidisation of the reactive elements forms a skin around the molten active solder, referred to as dross, forming a seal around the molten solder. To break the skin, mechanical agitation is provided to the molten active solder, step 102. This step is carried out at the surface of the first member to which the solder is to be applied. This allows the molten active solder to flow over said surface once the skin is broken.

[0062] Since the molten active solder is thermally activated at this point, the active elements in the active solder react with oxides on the surface of the first member in a redox reaction. This reduces the oxides on the surface of the first member leaving un-oxidised surface exposed to the solder. This allows the molten active solder to wet the surface of the first member causing the solder to adhere to said surface.

[0063] Once the molten active solder has adhered to the surface of the first member in this manner, the molten active solder is caused to cool, step 103. This is achieved by removing the heat source, which was maintaining the solder at a temperature above its melting temperature. This cause the solder to cool to a temperature beneath is melting temperature thereby causing it to solidify.

[0064] The process carried out to coat the surface of the second member is illustrated generally at 110 in FIG. 3. To coat the surface of the second member, a solder is heated at the surface of the second member causing the solder to melt, step 111.

[0065] The second member is not intended to be made of a niobium titanium alloy, however, any solder needs to be at about 20 degrees centigrade ( C.) to about 50 C. above its melting point to form a solder joint. This is referred to as the solder's joining temperature. Accordingly, the next step in coating the surface of the second member is to heat the solder to its joining temperature causing the molten solder to flow over said surface of the second member, step 112. As with the corresponding step in the process of coating the surface of the first member, this causes the molten solder to wet the surface of the second member and thereby to adhere to said surface.

[0066] The step of mechanically agitating the molten solder need only be carried out when the molten solder used to coat the surface of the second member is an active solder. This is the case in this example, but a non-active solder (i.e. a solder the composition of which does not include active elements) could be used as an alternative solder. Should a non-active solder be used, this step is optional. However, a flux would then be needed for the solder to wet the surface of the second member in place of the active elements of an active solder.

[0067] In a further parallel with the process of coating the surface of the first member, the molten solder is then caused to cool, step 113. Again, this is achieved by removing the heat source, which is maintaining the solder at a temperature above its melting temperature, thereby allowing the solder to cool and solidify.

[0068] In an alternative example, before the solder is applied to the surface of the second member, or instead of applying the solder to the surface of the second member, tin or a tin alloy is electroplated on to the surface of the second member pre-tinning the surface.

[0069] Returning to the joining method illustrated at 1 in FIG. 1, once the respective surfaces of the first member and second member are coated with solder the first stage of the process is complete and the second stage of the process begins. The second stage involves joining the coated surfaces together. This involves a number of steps, the first of which is that the first member and the second member are abutted together, step 12, forming an interface where the first and second members are in contact with the coated surface of each member close to the interface between the first and second members.

[0070] Once the first and second members are abutted against each other, heat is applied to the first member and the second member to heat each member to a temperature below the melting temperature of the solder coated on each member, step 13.

[0071] The coatings on each of the coated surfaces are then heated further to re-melt the solder, step 14. Depending on the quantity of solder that is coated on the coated surfaces, if it is considered that more solder is needed or would be beneficial, additional molten active solder is applied at the interface between the first and second members (step not shown). In this example, all the solders (the solder coated on each of the first and second members as well as any additional solder) are the same active solder. Should one or more different solders be used however, each solder will need to be miscible or at least compatible with each of the other solders.

[0072] However, as is mentioned above, if active solder is used it will not just react with the surface oxides on a niobium titanium alloy, but also with the oxygen in the atmosphere; as a result oxides will have formed on the surface of the solder forming a dross skin. Accordingly, mechanical agitation is again applied to the molten solder, step 15. This causes the dross skin to break up allowing (un-oxidised) molten solder on the coated surface of each of the first member and second member to come into contact, merge and form a continuous body of molten solder.

[0073] The continuous body of molten solder provides a link between the first member and the second member because the molten solder continues to adhere to the surface of each of the first member and the second member once merged. Once this is achieved, the molten solder is caused to cool again, step 16, solidifying the solder forming a solder joint between the first member and the second member. As with each of the coating processes, this is achieved by removing the heat source thereby causing the solder to cool beneath its melting temperature and solidify.

[0074] Should a non-active solder have been used to coat the surface of the second member, as mentioned above, a flux will be used. Accordingly, an additional step of removing any flux residue will be needed before mechanical agitation is applied to the molten active solder. This will avoid the flux residue being present in the continuous body of molten solder and potentially weakening the resulting solder joint.

[0075] The process illustrated in FIG. 1 is a two-stage process because the surfaces of the respective members are tinned and then joined. Referring now to FIG. 4, a process of a second example joining method is illustrated generally at 2. Instead of a two-stage process, such as the process illustrated in FIG. 1, the process illustrated in FIG. 4 is a one-stage process.

[0076] Generally speaking, the process illustrated in FIG. 4 is a one-stage process because the whole process is able to be carried out in a single joining process. This is instead of any component that is involved in the process being pre-prepared as is the case in the process illustrated in FIG. 1 with the tinning of the surfaces of the respective members.

[0077] Turning to the details of the process illustrated in FIG. 4, a surface of a first member made of a niobium titanium alloy and a surface of a second member are abutted together, step 20. This provides an interface between the first and second members. A molten active solder is then provided at said interface and heated to its joining temperature so as to thermally activate the molten active solder, step 21.

[0078] By providing the molten active solder at the interface, it is intended to mean either, that the molten active solder is provided within the interface, i.e. between the surfaces of the first and second members that are in contact, or that the molten active solder is provided at least one location on the perimeter of the interface between the first and second members.

[0079] Once the molten active solder is thermally activated, the thermally activated molten solder is mechanically agitated, step 22. This causes the dross skin, which forms on the solder as the active elements oxidise when the active solder is heated, to break. When the skin breaks, the molten active solder flows over each of the first and second members. This causes the solder to wet a surface of the second member over which it is flowing. Since the molten active solder is thermally activated, the molten active solder also wets a surface of the first member over which it is flowing by the same process as described above in relation to the process illustrated in FIG. 2. The mechanical agitation also causes the molten active solder to flow into the interface between the first member and the second member when the molten active solder has only been provided at the perimeter of the interface between the first and second members.

[0080] This results in the molten active solder adhering to the each of the first and second members and forming a continuous body of molten solder thereby linking the first member and the second member. Once the continuous body of molten solder is formed, the molten solder is caused to cool, step 23. This is achieved by removing the heat source that is maintaining the molten active solder at a temperature above its melting temperature. This forms a solder joint between the first member and the second member once the active solder has solidified.

[0081] Example Application of a Joining Method

[0082] Referring now to FIG. 5, an example application of forming a solder joint between a first member made of a niobium titanium alloy and a second member is generally illustrated at 3.

[0083] First however, details of the coaxial cable are provided. The coaxial cable has a standard structure in that it has a centre conductor or core, around which a dielectric material is provided. An outer jacket or shield is provided around the dielectric material. As mentioned above, the core and the shield are each made of a niobium titanium alloy. A typical dielectric material is polytetrafluoroethylene (commonly abbreviated to as PTFE) but other dielectric materials, such as polyether ether ketone (PEEK) and liquid crystalline polymer (LCP) can also be used.

[0084] The process illustrated in FIG. 5 is directed at forming a solder joint between the centre conductor of the coaxial cable and the centre pin of the connector and in a second step a solder joint is formed between the outer jacket of the coaxial cable and the connector body of the coaxial connector.

[0085] In one embodiment the outer diameter of the coaxial cable is about 1.195 millimetres (mm), the outer diameter of the PTFE dielectric is about 0.940 mm and the centre conductor outer diameter is about 0.287 mm. Other diameters of coax cables are available, which are governed by international standards. The process described here is equally applicable for other diameters of coaxial cables.

[0086] Turning to the coaxial connector, this is a standard RF coaxial connector of an appropriate size to connect with the coaxial cable. The coaxial connector used in this example is made of a gold plated beryllium copper alloy.

[0087] Returning to the processing of forming a solder joint between the centre conductor and shield of the coaxial cable and the coaxial connector, the first stage of this process is to coat an end portion of the coaxial cable core and shield with an active solder, step 30, and coat a surface of the connector pin and outer body of the coaxial connector with the active solder, step 31. Coating each of the end portions of the core and shield of the coaxial cable and the surface of the coaxial connector is a tinning process.

[0088] The active solder that is used in this example is made of an alloy including tin, silver, titanium, cerium, gallium and magnesium. The particular active solder used is active solder 220M produced by S-Bond Technologies, whose website can be accessed at: http://www.s-bond.com/.

[0089] The tinning process used to coat each of the core and shield of the coaxial cable with the active solder is the process illustrated in FIG. 2 and described above. Accordingly, to coat each of the core and shield of the coaxial cable, the active solder is heated above its melting point to its joining temperature to thermally activate the solder using a soldering iron. For active solder 220M, this is about 20 C. to 50 C. above the melting temperature (by this we intend to mean the joining temperature which is 20 C. to 50 C. above the liquidus temperature) of the solder.

[0090] For reference, the S-Bond active solder 220M has a solidus temperature (which we intend to mean the highest temperature at which the active solder is completely solid) of about 221 C., a liquidus temperature of about 232 C. and a joining temperature (i.e a temperature at which the active solder is capable of joining members together) range from about 250 C. to about 280 C. Between the solidus temperature and the liquidus temperature, the solder is partially solid and partially liquid (i.e. molten).

[0091] To protect the PTFE and reduce the possibility of melting the PTFE dielectric material, the length of time the solder is molten is minimised. PTFE has a melting temperature of about 327 C. and a maximum operating temperature of about 260 C. To minimise the amount of time the PTFE is subject to elevated temperatures the heat applied for the solder process is split between the solder process for the core and the shield of the coaxial cable.

[0092] When the active solder is thermally activated (and therefore molten), to coat the solder on to the respective component of the coaxial cable, the thermally activated molten active solder is mechanically agitated at an end portion of each respective component. At this stage, the mechanical agitation is generated by ultrasound produced by the soldering iron, which is an ultrasonic soldering iron. As explained above, this causes the dross skin on the molten active solder to break allowing the solder to flow over and adhere to the component by reducing the oxide layer on the surface of the component and wetting the surface of the component. The soldering iron is then removed allowing the active solder to cool and solidify.

[0093] Solder is coated on to the surface of the coaxial connector by the same process as the solder is coated on to the core and shield of the coaxial cable. However, since the coaxial connector is not made of a niobium titanium alloy but typically has a surface layer which is designed to allow it to be easily wetted, coating the connector with active solder is much easier although mechanical agitation is recommended. Accordingly, the surface of the coaxial connector is coated using the process illustrated in FIG. 3 and described above. As such, the active solder is melted using a soldering iron. Mechanical agitation, again, in the form of ultrasound produced by the soldering iron is then applied to the solder at the surface of the coaxial connector causing the molten solder to flow over and adhere to the surface of the coaxial connector by wetting the surface. Once this has occurred, the soldering iron is removed, which allows the solder to cool and solidify.

[0094] As an alternative to using active solder to coat the connector, because the connector is not made of niobium titanium alloy, a non-active, i.e. standard, solder can be used instead of an active solder. In this alternative, the standard solder is a flux cored solder. This is applied to the connector through a standard procedure for coating or pre-tinning a surface, such as by heating the surface to which the solder is to be applied using a soldering iron and providing the solder at the heated surface. This causes the solder to become molten and flow on to the heated surface. The soldering iron can then be removed to allow the molten solder to solidify on the surface to which it has been applied. When a solder with flux is used to tin the surface of the coaxial connector, any excess flux is removed by cleaning the coated surface.

[0095] We have found that the final solder joint appears smoother when using a combination of active solder on the niobium titanium alloy and a non-active solder on the coaxial connector. However, we have found no differences between the qualities of the final solder joints.

[0096] Once the coaxial cable and coaxial connector are coated with solder, the first stage of the process of FIG. 5 is complete. The second stage of the process of joining the coaxial cable and coaxial connector is achieved by first mounting the centre pin of the coaxial connector and second the connector body in a rotatable clamp.

[0097] In a first step, the centre pin of the coaxial connector is soldered to the centre conductor of the coaxial cable, the coaxial cable having been suitably prepared in advance. Solder is applied to the centre pin as explained above, then the centre pin of the coaxial connector is mounted into a rotating clamp. The end of the coaxial cable at which the core and shield have been tinned is guided into the centre pin of the coaxial connector causing the surface of the coaxial connector pin and the core of the coaxial cable to abut together, step 32. A hot air gun is then used to warm the core of the coaxial cable and the pin of the coaxial connector, step 33. As noted above, the warming does not raise the temperature of the components above the melting temperature of the solder on either the coaxial cable or the coaxial connector.

[0098] When the centre pin of the coaxial connector and the centre conductor of the coaxial cable are pre-heated, while continuing to use the hot air gun on each of the components, the solder(s) is/are melted using a soldering iron, step 34.

[0099] As an alternative to heating the solder(s) with a soldering iron, it is possible to heat the coaxial cable and/or coaxial connector using resistive soldering techniques. To achieve this, a conductive contact, such as a pair of conductive tweezers, is placed against the coaxial cable and/or coaxial connector. This forms an electrically conductive connection to the cable and/or connector. A current is then passed from the conductive contact into the cable and connector. This causes heat to be generated in the cable and connector through resistive heating. A rapid rise in temperature occurs due to the resistive heating raising the temperature of the surface of each of the coaxial cable shield and core and coaxial connector above the melting point of the solder coating on each component. This occurs within a short period of time, such as within a few seconds, for example in less than ten seconds or in less than five seconds. Once the solder coatings are molten the resistive heating can optionally be stopped by no longer applying a current through the components. By applying such a rapid increase in temperature and then removing the source of heating, we have found that there is a reduced likelihood of the joint formed between the active solder and the surfaces of the coaxial cable on to which it is coated failing due to the limited period that joint is exposure to raised temperatures.

[0100] Once the solder coatings are melted, the rotatable clamp is rotated causing rotation of the coaxial connector pin relative to the coaxial cable, step 35. Due to the surfaces of the inner diameter of the centre pin of the coaxial connector and outer diameter of the centre conductor of the coaxial cable being abutted, the relative rotation of the components causes mechanical agitation in the molten solder and disruption of oxide layers on the niobium titanium and causing the breakup of the dross skin of the molten solder. Extra mechanical agitation is able to be applied to the molten solder in the form of ultrasound produced by the soldering iron (which is an ultrasonic soldering iron) in addition to the mechanical agitation caused by the rotation of the coaxial connector relative to the coaxial cable or if the mechanical agitation caused by the rotation of the coaxial connector relative to the coaxial cable is insufficient to break the dross skin on one or each of the components. The breakup of the dross skin causes the molten solder coated on the pin of the coaxial connector and outer diameter of the centre conductor to merge, forming a continuous body of molten solder.

[0101] Once the continuous body of molten active solder is formed, the rotation of the rotatable clamp is stopped and the soldering iron is removed, step 36. This causes the solder to cool and solidify thereby forming a solder joint between the coaxial cable and the coaxial connector.

[0102] In the second step, in order to complete the coax assembly, the coaxial connector body is mounted in the rotating clamp. The sub-assembly of the centre pin of the coaxial connector which is soldered to the centre conductor of the coaxial cable is then inserted into a connector bore of the coaxial connector body in a suitable manner (this usually being as set out by in instructions for the coaxial connector body provided by the supplied) until an end stop in the connector bore.

[0103] The inside of the bore of the connector body is coated with active solder in accordance with the techniques described above, or if standard solder is used and flux was applied to ensure good wetting of the surfaces, the flux has to be removed. The outer conductor of the coaxial cable is then soldered to the connector body as described above in relation to forming the joint between the centre pin of the connector and the centre conductor of the coaxial cable.

[0104] As set out above, the core and shield of the coaxial cable are made of niobium titanium alloy. The alloy is used without also using a matrix or carrier of another material such as copper or a copper nickel alloy.

[0105] Also as set out above, while the first member is made of niobium titanium alloy, which is superconducting at cryogenic temperatures, the second member (corresponding to the coaxial connector in the example above) is made from a material that is non-superconducting at cryogenic temperatures (for example at temperatures between about 77 K and about 4 K). Accordingly, only one of the first and second members is superconducting. However, in the examples described herein, each of the first and second members is a metal or metal alloy.