METHOD OF MANUFACTURING THIN CONDUCTORS ON A CARRIER WEB AND THE CONDUCTOR MANUFACTURED WITH THIS METHOD The invention relates to a method of manufacturing thin metal or metal alloy electrical conductors by electrodeposition onto a carrier web. The surface of the carrier web is partially covered with a non-conducting layer and conductors of the desired form are deposited onto the electricity-conducting points that remain bare. The carrier web is taken to an electrodeposition bath, where there are at least one anode and a cathode. The carrier web rotates around support rolls and the cathode, and the conductor foil deposited from the salt solution attaches itself onto the carrier web. The carrier web is brought to electrodeposition as a reel and conductor foils are also coiled after the formation of individual conductors onto a carrier web reel for further processing, which can be performed in the desired location.

Thin conductors with good electrical conductivity are needed in several technical applications. When one wishes to produce flexible, flat cable (FFC), it is done at present by forming a cable from several copper wires in parallel, to both ends of which insulation is attached, such as paper or plastic web.

Generally the insulation web is polyester. The advantage of the conductor is good electroconductivity, a flat shape and good mechanical durability. This kind of conductor is described in for instance US patent application 2002/0062558 and US patent 6,492, 595. The cable is manufactured in the same way as a flexible printed circuit (FPC), but in manufacturing printed circuits part of the copper is etched away to achieve a certain circuit pattern.

The cable widths at present are in the range of 0.5-3 mm and the thickness less than 1 mm. The cables are used in the automotive industry, printers, CD and DVD players, televisions, satellite decoders etc. , and their scope of application is increasing rapidly.

In the prior art a method is known for producing a thin foil by electrolytic deposition. In the method there is a rotating cathode drum in an electrolysis

tank and a curved anode made of one or more parts on the bottom of the tank. The electrolyte is fed between the anode and the cathode and as a result a copper foil is deposited on the surface of the cathode drum. When the electrodeposited foil rises above the electrolyte, it is removed from the cathode and taken for further processing. The method has been developed since the 1930s and is described for instance in US patent 2,044, 415 and US patent application 2002/5363.

Electrolytic foil manufacture has focused, however, on producing a continuous foil, of which the superfluous metal is etched away for instance in the manufacture of conductors and microcircuits. Etching occurs after the foil has been laminated to for example a PVC substrate. A resist is applied on top of the copper foil, and it is exposed into the desired form through a mask.

The exposed resist is developed and the section of copper foil left outside the resist is etched away. After this, the resist is removed from the surface of the remaining copper foil product. The foil product is for example a microcircuit current conductor or a smart label conductor.

US patent 4,053, 370 describes a method whereby printed circuit patterns are fabricated electrolytically. In the method, the surface of an endless strip is covered with an insulating layer so that the electricity-conductive parts that remain exposed are of the desired product shape. The strip is placed in an electrolytic bath and rolled around a cathode drum. The electrolysis tank contains an acidic copper salt or electrolyte. Anodes are also immersed in the tank, which are preferably at different distances from the cathode drum and thus the strip onto which the circuit patterns are deposited. The first anode is nearer the strip, which facilitates the majority of the pattern to be deposited as a dense crystal structure. The second anode is located further away from the strip and as a result a rougher surface layer is obtained on top of the pattern. A rougher surface helps the adhesion of the pattern to the adhesive laminate.

The method described in US patent 4,053, 370 is based on the fact that the insulation of the endless strip, the formation of the circuit patterns and the removal of the patterns are all performed in the same unit. When circuit patterns are deposited in the same place where the circuit boards are produced, this is a practical solution. On the other hand however, it is more important that the pattern formed on the carrier substrate can be transferred attached to the carrier substrate and transported to its permanent location at a later date.

Now a method is presented for the fabrication of very thin, metal or metal alloy electrical conductors directly by electrodeposition, whereby functional conductors of the desired final shape are deposited directly onto the surface of a carrier web. Highly electroconductive material is used for the conductors such as copper, silver or gold, but in some connections the metal could also be nickel. The metal or metal alloy is in the electrodeposition tank as a metal salt solution, so that highly electroconductive conductors are deposited from it electrolytically. Thin conductive aluminium foil is used as the carrier web on top of which the conductor is deposited. The carrier web is brought to electrolysis as a reel and the conductors are also coiled after the formation of the conductors onto a carrier web reel for further processing, which can be performed in the desired location. Later we mention conductors when referring to a functional product, although the desired product may be something else. When we use the term electrodeposition or electrolytic deposition in the text, it means the same thing.

It is possible to form electrical conductors other than ribbon-like conductors by electrolytic deposition. Conductors can be made for example in the shape of twisted twin cable. Twisted twin cable is an advantageous shape for a conductor, because it differs from parallel cables in that the electromagnetic losses and disturbances in a twin cable are eliminated. The shape of the conductor can also be something other than ribbon-like or twin cable.

The essential features of the invention will be made apparent in the attached claims.

In the first stage of conductor fabrication, conductor-shaped patterns are made on top of the carrier web, aluminium foil, using a suitable method, for instance a printing method, where the shape of the future conductor is left unprotected. The insulating treatment of the carrier web is performed either in the same unit as the subsequent electrodeposition or in a separate unit. In the following stage the carrier web on the reel is straightened out and carried to an electrolyte bath, where the conductor shape is deposited on top of the untreated part of the surface of the web. The electric current density used and the speed of rotation of the drum determine the thickness of the copper layer that is generated. The current density and speed of rotation may vary within a wide range. The conductor may be further coated with fine-grained copper and/or brass or the conductor surface may itself be oxidized with a method of the prior art. Coating and oxidation increase the adhesiveness of the conductor to the laminate.

When the conductor has received the desired shape and further treatment, the carrier web is coiled onto the reel from which the conductors are attached in a separate work stage to a laminate or other operating substrate. After this, the carrier web is peeled off the operating substrate.

The method according to the invention is described further by means of the attached principle drawings, where Figure 1 is a principle drawing of one method according to the invention, where the conductor is formed on to a carrier web to be coiled, Figure 2 presents a principle drawing of another embodiment of the invention, and Figure 3 is a principle drawing of a flat twin cable.

Figure 1 shows that a carrier web 1 made of aluminium foil is brought on a reel 2 for electrolytic deposition. Before this, conductor-shaped patterns are formed on top of the carrier web, so that the place for the conductor shape remains uncovered and an insulating layer is formed on the other parts.

Where necessary, insulating treatment can of course be carried out just prior to electrolysis. The insulation of the surface can be carried out for example using the printing technique, by painting or gluing an insulating foil onto the surface of the carrier web. The carrier web is taken by means of support rolls 3 to the electrodeposition tank 4, which is equipped in at least one part with a forming anode 5 and a rotating roll-like cathode 6. The electrodes are connected to a power supply (not shown in detail in the figure). The tank 4 contains an electrolyte 7, which in the example case is a copper salt solution, for instance copper sulphate solution, which includes necessary additives. As mentioned above, the salt solution may also be a salt solution of some other metal or metal compound. The electrolyte is made to circulate in the space between the anode and the cathode and from there back to the tank outside the anode. Thin, conductor-shaped, conductor foils 8 of 5-500 micrometers thick are deposited from the electrolyte onto the surface of the surface- treated carrier web. The conductor foils are marked in the drawing much larger than they are in relation to the manufacturing equipment. The washing and drying of the conductors are known in the prior art so they are not shown in detail in the drawing.

Surface treatment may be performed on the conductors formed on top of the carrier web. The surface treatment stage may be for instance electrolytic copper plating or electrolytic brassing in a tank 9, in which there are a cathode drum 6 and anode 5 of the same type as in the actual conductor deposition treatment. The electrolyte solution is selected in accordance with the desired coating. The surface treatment of the conductors makes the conductors adhere better to the operating substrate. After further treatment, the conductor-containing carrier web is rolled onto a reel 10 for further processing. When the conductors are left on the carrier web, it is easy to

deliver them on reels to a further manufacturer, who can peel off the conductors from the carrier web and attach them to the operating substrate of their choice.

The principle drawing in Figure 2 shows another circulation method for a carrier web in an electrodeposition bath. Patterns in the shape of a conductor are formed on top of the carrier web 1 so that the places for the conductor remain bare and an insulating layer is formed on the other parts.

The carrier web 1 is brought to the electrodeposition stage on a reel 2.

There is an electrolyte 7 in the tank 4, which in the case of the example is a copper salt solution, for instance copper sulphate solution, which includes the necessary additives. In this alternative several plate-like anodes 11 are located in the tank. The carrier web moves between the anodes by means of the roll-like cathodes 12 situated above the tank and the support rolls 13 situated in the tank. The anodes are situated between the cathode rolls. The electrodes are connected to a power supply (not shown in the drawing). As a result of this treatment conductor patterns of the desired shape are deposited on top of the carrier web. If surface treatment is required on top of the conductor patterns, it can be made in the corresponding method to that described in connection with Figure 1, using either one or more cathode rolls.

Figure 3 presents a principle drawing of one conductor 8 manufactured in a way according to the invention. It is also possible to manufacture conductors by electrolytic deposition which have a different shape than a straight ribbon.

For example, a flat twin cable like that shown in the drawing can be manufactured directly in the cable shape without separate manufacturing steps, such as the attaching of webs to each other and etching. There is only one example in the drawing of a product which can be manufactured, since obviously the conductor can also have a shape other than that of a twin cable.

When inexpensively priced aluminium foil is used as carrier web, the various manufacturing stages of the conductor can be differentiated in specialized units. Thus one unit may handle surface treatment, the next the formation of conductors and the third the forming of the actual cable on the operating substrate. The foil thickness is chosen according to need, but in general the foil thickness is in the range of 10-500 micrometres. It is preferable to route the aluminium foil back to smelting for example after peeling off the conductors. Foil that is wrapped around a reel in the transportation stage protects the conductors from the effect of the environment.