GB2278615A - Metal spraying - Google Patents

Abstract

A method of using metal vapour spraying in order to deposit a film of metal onto a target material, where the target material may have a relatively low melting point, and without the use of adhesives. The rate of deposition and spacing between the vapour gun and target is controlled. The deposition is carried out in ambient conditions, rather than in vacuum. It provides a quick way of laying out conducting layers, in patterns, onto materials which may have an irregular or uneven shape as illustrated in Fig 1. The target may be plastic or glass reinforced plastic. A shadow mask may be placed near or on the surface of the target material and the method finds particular application is the manufacture of printed circuits. <IMAGE>

Description

MATERIAL METALLISATION This invention relates to a method of applying metallic films to surfaces which may be uneven, without the use of adhesives, by means of vapour deposition in air.

There are many methods in current use for applying layers of metals to other materials.

Where the target material has a relatively low melting point (say 50 to 200"C) and may be thin, then current methods dictate either the attachment of a metal film using adhesives, or the use of metal vapour/plasma deposition in a vacuum. Both of these methods have their limitations; it can be difficult to impossible to apply a metal film with adhesives to an irregularly shaped target material. The vacuum vapour deposition method does require a vacuum chamber, with consequent cost and awkwardness of application.

A method has thus been devised using commercially available metal vapour spraying equipment, operating in air and under usual environmental conditions. The rate of metal deposition and temperature of the metal vapour / liquid droplets is controlled by the nozzle diameter of the vapourising gun, the rate of feed of the stock metal, the distance from the target material, and the rate of traverse with respect to this material.

Two examples of the method will now be described, with reference to the accompanying drawing in which : Figure 1 shows an uneven material being metallised; Figure 2 demonstrates the use of masking to produce a matallic pattern: and Figure 3 illustrates a possible resulting pattern.

Referring to Figure 1, the metal vapour gun 1 (gas, power and wire feed via conduit 2, mainly not shown for clarity) is suspended at an approximately fixed distance from a target material 4. The example in this figure has an uneven surface, and may be a plastic or composite, for example glass reinforced plastic, Cobex, Bextrene, or other materials which may start to soften at temperatures as low as 500 C. Even materials as thin as 0.5mm have been successfully plated; there is no reason to believe that the method of vapour spraying, with the correct distance and traverse rate may not work on any thickness of target material. The vapour gun is traversed across the surface at a constant rate.This rate and the distance from the target are critical; too far from the surface and the metal forms a film lying on the surface of the target, which may become detached.

If the gun is too close, or the traverse rate too low. then the heat from the metal vapour causes the target to distort, or in excessive cases, burn or even vapourise. Between these two extremes, the vapour striking the surface partially and locally melts the target material, thus adhering to it, without bulk heat transfer to the target material. The metal thus deposited becomes a permanent, non-removeable laver. Experiments have shown that the two parameters mentioned may be varied by about 30-40%. After the first pass, repeated passes may be made to deposit a thicker layer. The traverse rate and distance of the gun are not so critical at this stage, as the metal already deposited protects the underlying material. The resulting film displays good conduction, and may be burnished if a fine finish is required. In the drawing, the direction of traverse is indicated 3, together with the deposited layer 5.

In Figure 2, the same method is applied to a material 6, (also show in Figure 3), with a shadow mask 7 being interposed between the vapour gun 1 and the target 6.

Complicated patterns can be applied in a single pass of the gun.

Among the potential applications are printed circuit manufacture, deposition of circuits on curved loudspeaker elements, EMC screening of sonar domes, EMC screening of composite materials used in modern aircraft manufacture, metallising of composite fuel tanks as part of static electricity avoidance and coppering the hulls of boats made of plastics and composites.

Claims (5)

1. A method of efficiently applying permanent metallic layers to other substances, where the target may have a relatively low melting point, and without the use of adhesives. This method makes use of metal vapour spraying, controlling the adhesion of the vapour and avoiding melting of the target by controlling the rate of deposition, and spacing between vapour gun and target. The target may be irregular in shape.
2. 2 A material metallising technique as claimed in Claim 1, where a shadow mask may be placed near or on the surface of the target material, thus enabling rapid deposition of conducting patterns.
3. 3 A material metallising technique as claimed in Claim 1 or Claim 2 above, whereby printed circuits may be effected on many non-conductors for purposes of either electical conduction, EMC (electro-magnetic compatability) screening, or optical effects.
4. 4 A material metallising technique as claimed in claim 1 or claim 2 above, where the metal deposit is made for aesthetic reasons.
5. 5 A material metallising technique as claimed in claims 1 to 4 above, where the traverse rate and height of the vapour gun may be controlled by automatic equipment or manually.