The invention relates to apparatus and a process for producing copper-clad dielectric material.

Published International Patent Application WO 85/02969 describes a process in which copper deposited on a press plate is bonded to dielectric material in a laminating press. The resulting copper-clad dielectric board separates from the press plate, which can then be re-used. The treatment of individual press plates is time-consuming and involves intermittent physical manipulation of the press plates between treatment baths. What, is desired is a process which can produce copper-clad dielectric material continuously.

US Patent 2 433 441 describes a method of manufacturing an extremely thin metal foil, in which an endless stainless steel band passes round a roller in a metal plating bath, then passes round a roller in a washing bath, and subsequently passes round a roller in a bath containing a film-forming material; finally the film is dried and the composite strip of metal and reinforcing t i lra is mechanically stripped from the endless band .

US Patent 4 L 13 S76 describes a method of making a thin copper (oil plastics composite, in which a

chromium-plated stainless steel belt passes round rollers guiding it on a sinuous path through various copper deposition and treatment baths. On a horizontal run of the belt fusible solid plastics particles are deposited on the copper and heated to form a plastics layer, which is then removed together with the copper.

The methods described in these two US patents have not achieved practical utility.

German Offenlegungschrift DE-A1-35 15 629 describes a process in which resin-impregnated sheets are passed through a double belt press whose belts are coated with copper by electrodeposition, so a copper-coated laminate separates from the press belts after the resin curing zone. This process has also not achieved practical utility, owing to the difficulty of depositing a copper layer of suitable quality on a press belt.

The aim of the present invention is to provide a process and apparatus which are relatively uncomplicated and which can produce good quality copper-clad dielectric material.

In one aspect the invention provides apparatus for producing copper-clad dielectric material, comprising:

(a) an endless belt;

(b) means for guiding the belt along a path having, in sequence, a substantially straight, substantially horizontal first run, a substantially straight second run, and a return run, with a non-abrupt transition

section connecting the first and second runs,

(c) means for depositing a copper layer on the outer surface of the belt on the first run;

(d) means for treating the copper layer on the first run so as to enhance its bonding to dielectric material;

(e) means for moving the belt so that the treated copper layer passes from the first run to the second run via the transition section;

(f) means for supplying dielectric material along a path having a section substantially parallel to and ^' adjacent the second run;

(g) means for bonding the dielectric material to the treated copper layer on the second run; and

(h) means for removing the resulting copper-clad dielectric material from the belt as it passes from the second run to the return run.

In another aspect the invention provides a process for producing copper-clad dielectric materia, comprising:

(a) guiding an endless belt along a path having, in sequence, a substantially straight, substantially horizontal first run, a substantially straight second run, and a return run, with a non-abrupt transition section connecting the first and second runs,

(b) depositing a copper layer on the outer surface of the belt on the first run;

(c) treating the copper layer on the first run so as to enhance its bonding to dielectric material;

(d) moving the belt so that the treated copper layer passes from the first run to the second run via the transition section;

(e) supplying dielectric material along a path having a section substantially parallel to and adjacent the second run;

Cf) bonding the dielectric material to the treated copper layer on the second run; and

(g) removing the resulting copper-clad dielectric material from the belt as it passes from the second run to the return run.

It is easy to make the minimum radius of curvature of the transition section sufficiently large that the treated copper layer remains intact and adherent to the belt as it passes from the first run to the second run.

Since the belt remains substantially horizontal during copper deposition and treatment, flexing of the belt is avoided during these steps, thereby avoiding damage to the copper layer or premature separation of the copper layer from the belt.

The second run may be in alignment with the first, although this would require much space, but preferably it is either substantially vertical, extending upwards (or downwards) from the first run, or substantially horizontal and parallel to the first run.

The belt is preferably a polished metallic belt (e.g. stainless steel, titanium, or chromium-plated steel) and is preferably polished on the return run of its path. In a preferred process a copper layer substantially free of micro-pores is directly deposited on the belt and is then provided with a matte surface of copper of dendritic structure, for instance by the techniques disclos-ed in WO 85/02969. The matte surface may be subjected to further treatment before bonding to the dielectric material. Bonding preferably involves the application of heat and pressure followed by cooling, the forces generated at the interface of the polished belt and the treated copper layer, owing to. the penetration of the dielectric material into the dendritic structure under pressure and the subsequent cooling of the dielectric material, preferably being sufficient to overcome the adhesion of the copper layer to the polished belt.

The depositing and treating means preferably comprise a series of electrolytic baths through which the first run of the belt passes. It may be possible to arrange for the liquid level in each bath to substantially coincide with the outer surface of the belt, but it is preferable for the belt to be immersed in the liquid in each bath and to enter and leave each bath via sealing means. Such sealing means preferably comprise rollers in contact with the outer surface of

the belt, to minimise friction on the deposit and avoid abrasion. The inner surface of the belt may be contacted by rolling or fixed sealing members.

The outer surface of the belt is preferably washed between each electrolytic bath, e.g. by a water spray.

Cathodic electrical contact with the belt is preferably made between at least two of the electrolytic baths. The contact is preferably with the inner surface of the belt, to avoid damaging the outer surface and/or the deposit, and is preferably made by a spring-loaded contact element. The outer surface is preferably supported by a roller or rollers, to prevent distortion of the belt by the force of the electrical contact.

Preferably, two endless belts with corresponding depositing and treatment means are arranged with their second runs substantially parallel to each other, with the path of the dielectric material running between them.

The invention will be described further, by way of example, with reference to the accompanying schematic drawings, in which:

Figure 1 shows apparatus for producing copper-clad dielectric material, utilizing two endless belts;

Figure 2 shows electrolytic deposition and treatment baths associated with the lower horizontal run of one of the baths; and

Figure 3 shows part of two adjacent baths, on an enlarged scale.

The apparatus illustrated has two endless polished stainless steel belts 1 which pass continuously around guide rollers 2 on a roughly square path including a first, horizontal run 3 and a second, vertical run 4 connected by a convex transition section 6. Each belt 1 is driven at a constant speed in the direction of the arrow 7 by suitable drive means (not shown).

The first run 3 of each belt 1 passes through an electroplating plant 8 in which a copper layer is applied to the outer, lower surface of the belt 1 and is treated to enhance its bonding to dielectric material. The second runs 4 of the belt 1 pass through a vertically arranged double belt press 10 (the press belts are not shown) in which the treated copper layers on the facing outer surfaces of the belts 1 are bonded to dielectric material supplied in the form of continuous sheets 9 (e.g of epoxy resin impregnated glass cloth) from supply rolls 11. The resulting two-sided copper-clad laminate 12 separates easily from the belts 1 as they pass from the vertical to a horizontal stretch of a return run 13. The laminate 12 is withdrawn vertically and cut into sheets. On the return run 13 the belt is washed with high pressure jets to remove contaminating particles and oxidation and is lightly polished by a rotating brush 14.

The belts 1 are thinner than the press belts but are sufficiently thick (e.g. 1 or 2 mm) to carry the current necessary for electroplating.

The electroplating plant 3 is illustrated in more detail in Figure 2. The horizontal run 3 of the stainless steel belt 1 passes through a series of electrolytic baths 16-21 in which the surface 22 of the electrolyte is above the level of the belt and an anode 23 is arranged immediately below the lower surface of the belt. The belt 1 enters and leaves each bath through a sealing device 24 comprising idle rubber-faced rollers 26 and 27 engaging the respective upper and lower surfaces of the belt 1 and engaging respective resilient rubber sealing strips 28 and 29 fixed to a wall of the bath. Some electrolyte will inevitably escape through the sealing device 24 and is caught by a trap 31 having a drain outlet 32. Electrolyte is wiped off the upper surface of the belt 1 by rubber wipers 33. Fresh electrolyte is supplied to each bath through a suitably positioned inlet pipe 34 having an outlet 36 (a slit or aperture) directing the electrolyte between the belt 1 and the anode 23. Thus controlled throughput of electrolyte is possible.

Between each adjacent pair of baths the lower surface of the belt 1 is washed with water from spray bars 37. At the same positions, spring-loaded contact blocks 38 make cathodic electrical contact with the

upper surface of the belt 1, and the belt is supported by large-diameter rubber-faced rollers 39 below the blocks 38.

In the first bath 16 a first, pore-free copper layer 1 to 2 μm thick is deposited from an electrolyte containing copper pyrophosphate. In the following three baths 17-19, containing acidic copper sulphate solutions, the copper layer is built up to a thickness of 3 to 12 μm and treated in a well-known manner so that its exposed surface has a dendritic structure suitable for bonding to the dielectric material. In the next bath 20, in which the electrolyte contains zinc sulphate, a very thin layer of zinc, which is insufficient to reduce the bond strength appreciably, is applied in order to prevent chemical reaction between the copper and the epoxy resin. Finally, in the last bath 21, the plated layer is passivated in a weak chromic acid solution.

The time of each deposition or treatment step in the baths 16-21 depends, of course, on the length of the bath and the speed of travel of the stainless steel belt 1. The dimensions of the belt are determined by the output required and the nature of the copper-clad laminate to be produced.

Preferably, the anodes 23 are perforated. In the bath 16 this enables air to be blown up through the anode, allowing the current density to be increased. In

the following baths, gases produced in the gap between anode and belt can escape through the perforations, enhancing uniformity of deposition. Consequently, using perforated anodes, an increase in plating speed by a factor of 2 or 3 may be achieved.

In the press 10 the belt runs 4, with the dielectric material sandwiched between them, pass between a pair of endless press belts (not shown) while heat and pressure are applied followed by cooling under pressure. Such double-belt presses are already known in the art of laminating and are, for example, made by the German company, Hymmen GmbH.

Various modifications may be made within the scope of the invention as described above. For example, it may be possible for the electroplating plant to be associated with an upper horizontal run of the belt and for the plated belt to descend through a vertical run, the dielectric material being supplied from above and the resulting laminate being discharged below the apparatus; the anodes 23 will in that case be above the belt.

If a horizontal double-belt press is to be used, instead of the vertical press described above, then the two electroplating plants are arranged respectively above and below the press. The first runs of the belts 1 are parallel to the second runs, and each belt 1 passes round large-diameter rollers and travels in a generally vertical direction from the first run to the second run.