GB2144064A

GB2144064A - A method of soldering together two surfaces

Info

Publication number: GB2144064A
Application number: GB08320614A
Authority: GB
Inventors: Murrey Bates; Douglas Field
Original assignee: Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1983-07-30
Filing date: 1983-07-30
Publication date: 1985-02-27
Also published as: GB8320614D0

Abstract

A method of soldering together two identical aluminium components includes degreasing the components and masking all but the surfaces to be soldered with tape 7. One component is then grit- blasted to give a roughened surface. Copper is sprayed on to the component to give a layer 8 and then solder is sprayed on, giving a second layer 9. The solder will adhere to the copper layer 8, whereas it will not adhere to aluminium. Flux is then applied, with additional solder, and the other component, to which identical processes have been applied, is placed adjacent the first with soldered surfaces in contact. The components are heated, the solder becomes molten and when allowed to cool, forms a bond. <IMAGE>

Description

SPECIFICATION A Method of soldering together two surfaces This invention relates to a method of soldering together two surfaces, at least one of which is made of a material to which the solder will not adhere. For example, aluminium surfaces cannot be conventionally soldered together.

The invention arose in consideration of alternative methods of joining together aluminium or aluminium alloy waveguide components, which are conventionally joined using the difficult process of aluminium welding.

One possible alternative method which was considered was to deposit copper on the surfaces of the components by electro-plating.

Then solder is applied to those surfaces which are to be mated. The copper, which remains exposed, must then be removed. These are lengthy processes. It is also difficult to remove and recover all of the copper which is not required and there are some applications where the presence of copper in the finished joined compents could be undesirable, for example, in microwave waveguides.

Another method which was considered was dip-brazing. Two components to be joined are placed in a bath of a molten joining agent which must include a corrosive flux. The bath must be maintained at a critical temperature.

The temperature may be very close to the melting point of the material of the components, which must therefore be carefully selected. If the actual composition of the material is different to that which it is believed to be, it could melt, contaminating the contents of the bath which must then be cleaned.

Furthermore, if, after dip-brazing, machining across the joint is required, acid traps in which acid salts from the corrosive flux are held may become exposed, allowing metal at the joint to corrode.

The present invention arose through efforts to find an improved method of joining aluminium or aluminium alloys.

The invention provides a method of soldering together two surfaces at least one of which is of a material to which the solder will not adhere, including spraying the said one surface with a substance which will adhere both to the said material and to the solder.

The material and the substance may be metallic, but the material could be plastics or some other composition. Application of the substance can be made quickly and easily by use of the spray and requires only a small amount to be used, with little wastage. The parameters governing the spraying process are not as critical as those in the dip-brazing process and the high temperatures needed for the latter process are not required. Hence the choice of materials which may be treated in this way is much wider. Also, the method is much more controllable than the previously known methods.

Preferably, the method includes spraying the said one surface with a solder spray after it has been sprayed with the said substance, although it could be applied in some other way. Spraying is, as with the application of the substance, a quick and easy process. If the solder is sprayed on to the substance as soon as possible after the substance has been applied, it may prevent any degradation or oxidation of the substance which may otherwise tend to occur. Preferably, further solder is applied to the said one surface after it has been sprayed with the solder spray, although the solder which has been applied by spraying may be sufficient.

The further solder could be the solder which is sprayed on, or a different one. For example, the solder which is sprayed may be a silver and tin alloy, such as B.S.219 Type 625, whereas the further solder is a tin and lead soft solder. Such a soft solder may not be suitable for spraying because of the health hazard of the lead. A non-corrosive flux is preferable to an active one. The flux acts as a wetting agent to encourage the solder to flow and cover the surface to which it is applied.

The invention is particularly applicable to the joining of aluminium or aluminium alloy surfaces. Preferably, copper is the substance used, especially with such aluminium or aluminium alloy surfaces.

Preferably, the said one surface is roughened prior to spraying it with the substance, for example by grit-blasting. This aids mechanical bonding between the material and the substance. However, this may not be necessary if the surface is already roughened or if the substance sprayed on to it is, for example, exothermic and undergoes metallurgical bonding.

It is preferred that a component including the said one surface is masked to expose only the said one surface. Thus the whole masked component may be sprayed and not just the said one surface. Masking could be effected by covering the desired areas with tape, which is easy to apply and remove once the spraying is complete.

The invention also provides a method for joining two components of aluminium or aluminium alloy including the steps of: degreasing the components, masking parts of the degreased components which are not to be mating surfaces; then spraying them with a copper spray, then spraying them with a tinsilver alloy solder, removing the masking from the sprayed components, applying soft solder and non-corrosive flux to the surfaces to be mated after the masking is removed, then removing the flux, then holding the mating surfaces together and heating the components.

One way in which the invention may be performed is now described by way of example with reference to the accompanying drawing, in which: Figures 1, 2 and 3 show schematically stages in assembling a waveguide section from two half portions in accordance with the invention.

With reference to Figure 1, a half portion 1 of a waveguide section is to be joined to another second identical half portion (shown in Figure 3 at 11). The half portion 1 is aluminium and comprises a base 2 with side walls 3 and 4 which extend upwards as shown and have a rectangular cross-section.

The half portion 1 is to be soldered along upper surfaces 5 and 6 (shown cross-hatched) of the side walls 3 and 4, to corresponding surfaces of the second half portion 11.

Firstly, the half portion of portion 1 is degreased. Then all its surface except those parts 5 and 6 which are to be soldered, are masked, using tape 7. The half portion 1 is grit-blasted to roughen its unmasked upper surfaces 5 and 6 to permit a good mechanical bond.

A metal spray gun is used to cover the upper surfaces 5 and 6 with a layer of copper 8 of a few hundreths of a millimetre width.

The copper-coated surfaces 5 and 6 are then sprayed, using the spray gun, with a tin and silver alloy solder, B.S. 219 Type 62S, to give a layer of solder 9 which is of similar thickness to the layer of copper 8 as shown in Figure 2. The masking tape 7 is then removed. It is desirable to apply the solder spray as soon as possible to cover the layer of copper 8 and prevent it oxidising.

Further solder is then applied with some heat to the layer of solder 9 with a noncorrosive flux known as a rosin. The further solder is a soft solder 60/40 tin and lead alloy. The flux is then removed.

The second half portion 11 is similarly treated to give a layer of copper 10 covered by a layer of tin and silver alloy copper.

The two half portions 1 and 11 are then placed in position with the layer of solder 9 of the half portion 1 in contact with the layer of solder on the corresponding parts of the second half portion. More heat is applied and any additional solder and flux required along the joint is added. The two half portions 1 and 11 are held together and excess solder wiped away. Since the solder will not adhere to the aluminium surfaces, it may be easily removed leaving them smooth. The solder solidifies and forms a bonding layer 12 between the two half portions 1 and 11 to give the completed waveguide section as shown in Figure 3. The flux is then removed.

This method gives a strong bond, but if it is required to withstand large stresses, mechanical fixing means such as screws or bolts may also be used.

Of course, this method may be used for many other applications, such as sheet metal work, for example.

Claims

1. A method of soldering together two surfaces, at least one of which is of a material to which the solder will not adhere, including spraying the said one surface with a substance which will adhere both to the said material and to the solder.

2. A method as claimed in claim 1 and including spraying the said one surface with a solder spray after it has been sprayed with the said substance.

3. A method as claimed in claim 2 and wherein further solder is applied to the said one surface after it has been sprayed with the solder spray.

4. A method as claimed in claim 2 or 3 and including applying a non-corrosive flux to the said one surface.

5. A method as claimed in any preceding claim and wherein the said one surface is of a material which includes aluminium.

6. A method as claimed in any preceding claim and wherein the substance is, or comprises, copper.

7. A method as claimed in any preceding claim and wherein the solder of the solder spray is an alloy containing tin and silver.

8. A method as claimed in any preceding claim and wherein the said one surface is roughened prior to spraying it with the said substance.

9. A method as claimed in any preceding claim and wherein a component including the said one surface is masked to expose only the said one surface.

10. A method for joining two components of aluminium or aluminium alloy, including the steps of: degreasing the components, masking the parts of the degreased components which are not to be mating surfaces, grit-blasting the masked components, then spraying them with a copper spray, then spraying them with a tin-silver alloy solder, removing the masking from the sprayed components,applying soft solder and non-corrosive flux to the surfaces to be mated after the masking is removed, then removing the flux, then holding the mating surfaces together and heating the components.

11. Apparatus including surfaces joined by the method of any preceding claim.

12. A method substantially as illustrated and described with reference to the accompanying drawings.